Patent Publication Number: US-7593668-B2

Title: Image forming apparatus with adjusting portions to adjust positions of conveying and discharge portions

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus, and more particularly, to a structure for accommodating different types of image forming units in an apparatus main body. 
   2. Description of the Related Art 
   A conventional image forming apparatus includes an image forming unit for forming an image on a sheet. The image forming unit includes elements such as an image writing unit including a laser scanner and an LED array, a photosensitive drum, primary and secondary chargers, a toner supply unit, a transfer unit, a toner collecting/cleaning unit, an image fixing unit, a drive unit, and a sheet conveying unit. 
   As examples of the image forming unit, there are known an image forming unit of a monochromatic electrophotographic system using one photosensitive drum, an image forming unit of a tandem-type color electrophotographic system using a plurality of photosensitive drums arranged in series, and an image forming unit of a rotary-type color electrophotographic system using a plurality of photosensitive drums to be rotated. 
   Up to now, there is one type of an image forming apparatus from which an image forming unit can be removed to an outside to be, for example, replaced with another image forming unit or repaired when a life of the image forming unit comes to an end. In the image forming apparatus, for example, an indication is given when the replacement of the imaging unit serving as a component of the image forming unit is required because of the end of the life thereof, and the imaging unit and the photosensitive drum are detachably mounted on the apparatus main body. Japanese Patent Application Laid-Open No. 64-26865 discloses an example of the image forming apparatus having such a structure. 
   In the conventional image forming apparatus including the image forming unit mounted in a replaceable manner, the replacement or the like of the image forming unit is possible. However, the image forming apparatus is not ready for a wide variety of the products (image forming unit) manufactured in recent years. In other words, while there are various image forming units using the electrophotographic systems mentioned above in a case where the electrophotographic systems to be used in the image forming units are different from each other, a position and direction into which a sheet enters and a position and direction into which a sheet is discharged are also different. In addition, a position of a heat source such as a fixing device, conditions of airflow (air pressure gradient) by the components are different from one system to another. 
   For this reason, it is difficult to entirely remove the image forming unit from the apparatus main body to incorporate another image forming unit having a different structure in the apparatus main body. Therefore, when, for example, the apparatus main body is recovered and a frame of the apparatus main body, that is, a support of the image forming unit is to be recycled, it is necessary to individually design the support in compliance with the type of an image forming unit to be newly incorporated in the apparatus main body. 
   Specifically, in the conventional image forming apparatus, even when the apparatus main body is to be recycled by replacing the image forming unit with another image forming unit, it is difficult to receive an image forming unit having a different structure from that of the image forming unit used until being recovered, in the apparatus main body. As a result, reuse of (the frame of) the apparatus main body or common use thereof cannot be achieved. Further, in a case where one apparatus main body is reused by another apparatus, there are problems in that, for example, a large number of designing steps are required, and management costs for the recycling are increased. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the above-mentioned circumstances, and therefore, an object of the present invention is to provide an image forming apparatus capable of selectively mounting different image forming units having different structures. 
   According to the present invention, there is provided an image forming apparatus including: an image forming unit; an apparatus main body which is capable of mounting the image forming unit; a sheet conveying portion which is provided to the apparatus main body, and conveys a sheet to the image forming unit; a sheet discharge portion which is provided to the apparatus main body, and discharges the sheet on which an image is formed by the image forming unit; a first adjustment portion which adjusts a connecting position of the sheet conveying portion with respect to the image forming unit mounted on the apparatus main body; and a second adjustment portion which adjusts a connecting position of the sheet discharge portion with respect to the image forming unit mounted on the apparatus main body. 
   Further, according to the present invention, there is provided an image forming apparatus, comprising: an apparatus main body capable of selectively mounting different image forming units of different types; a sheet conveying portion which is provided to the apparatus main body, and conveys a sheet to the image forming unit mounted on the apparatus main body; a sheet discharge portion which is provided to the apparatus main body, and discharges the sheet on which an image is formed by the image forming unit mounted on the apparatus main body; a first adjustment portion which adjusts a connecting position of the sheet conveying portion with respect to the image forming unit mounted on the apparatus main body; and a second adjustment portion which adjusts a connecting position of the sheet discharge portion with respect to the image forming unit mounted on the apparatus main body. 
   Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an appearance schematic view in which an exterior of a color printer, which is an example of an image forming apparatus according to an embodiment of the present invention, is removed. 
       FIG. 2  is a perspective view illustrating a state where an image forming unit of the color printer is drawn out. 
       FIG. 3  is an explanatory diagram of a structure in which an internal unit having the image forming unit of the color printer is drawn out. 
       FIG. 4  is a perspective view of a sheet discharge unit provided in a main body chassis of the color printer. 
       FIG. 5  is an explanatory diagram of a structure of the sheet discharge unit. 
       FIG. 6  is a perspective view for explaining a structure of a registration unit provided in the main body chassis. 
       FIG. 7  is a perspective view of a fan duct provided in the main body chassis. 
       FIG. 8  is an explanatory diagram of the fan duct. 
       FIG. 9  is another explanatory diagram of the fan duct. 
       FIG. 10  is a diagram illustrating a structure of the internal unit of a rotary type including an image forming unit capable of being mounted on the color printer and having another structure. 
   

   DESCRIPTION OF THE EMBODIMENTS 
   Hereinafter, best embodiment modes for carrying out the present invention will be described with reference to the drawings. 
     FIG. 1  is an appearance schematic view in which an exterior of a color printer, which is an example of an image forming apparatus according to an embodiment of the present invention, is removed.  FIG. 2  is a perspective view illustrating a state where an image forming unit of the color printer is drawn out. The color printer is a 4-drum full color printer using an intermediate transferring belt. 
   As illustrated in  FIGS. 1 and 2 , the image forming apparatus includes a color printer  1 , a color printer main body  2 , an image forming unit  10  including drum units  10   a  for four colors of yellow (Y), magenta (M), cyan (C), and black (Bk), an intermediate transferring belt  31  serving as an intermediate transfer member, and a fixing device  40 . The drum units  10   a  for four colors are arranged in parallel with each other along the intermediate transferring belt  31 , and includes photosensitive drums  11  serving as image bearing members. Further, on outer peripheral surfaces of the photosensitive drums  11 , there are provided a primary charger (not shown) for uniformly charging the surfaces of the photosensitive drums  11 , and a developing device  14  for developing an electrostatic latent image formed on the surface of the photosensitive drum through exposure by a laser scanner  13 . 
   Then, in the color printer  1  having the above-mentioned structure, when an image forming operation is started, in, for example, the drum unit for yellow, the surface of the photosensitive drum  11  is first uniformly negatively charged by the primary charger. After that, image exposure is performed by the laser scanner  13 , thereby forming an electrostatic latent image corresponding to a yellow image component on the surface of the photosensitive drum  11 . Then, the electrostatic latent image is developed using negatively charged yellow toner by the developing device  14 , and is visualized as a yellow toner image. The yellow toner image thus obtained is primarily transferred onto the intermediate transferring belt  31  by a primary transfer blade  17 . 
   Then, the toner image forming operation is performed at a predetermined timing in the other drum units, and toner images formed on the photosensitive drums  11  are sequentially superimposed on the intermediate transferring belt  31  to be primarily transferred by the primary transfer blade  17 . Next, the four toner images transferred onto the intermediate transferring belt  31  are moved to a secondary transfer portion including the intermediate transferring belt  31  and a secondary transfer roller  35  through rotation of the intermediate transferring belt  31 . 
   On the other hand, a sheet is fed from a cassette  20  or a multi-feed tray  25  in parallel with the toner image forming operation, and the sheet is conveyed to the secondary transfer portion in synchronization with the toner image formed on the intermediate transferring belt  31  by a registration roller pair  23  of  FIG. 6  to be described later. 
   Then, after the color toner images are formed in the manner as described above, in a case where the toner image is formed only on one surface of the sheet, the sheet is discharged to a discharge portion  64  disposed on an upper surface of the apparatus main body  2  through discharge rollers  206  by switching a change flapper  61  of  FIG. 5  to be described later. 
   On the other hand, in a case where the toner image is formed on both surfaces of the sheet, the sheet onto which the toner image is fixed by the fixing device  40  is conveyed in a direction of the discharge portion  64  by the discharge rollers  206 , and the discharge rollers  206  are reversely rotated after a trailing edge of the sheet has passed through the flapper  61 . 
   In this case, after the trailing edge of the sheet has passed through the flapper  61 , the flapper  61  is moved downward by its own weight to open a duplex conveying path  70  of  FIG. 5  to be described later. Thus, through the reverse rotation of the discharge rollers  206 , the sheet is conveyed to the duplex conveying path  70 . After that, through the reverse rotation of the discharge rollers  206 , the sheet reaches the registration roller pair  23  through a conveying path  73  forming a re-conveying path with the duplex conveying path  70 . At this time, the surfaces of the sheet are reversed, and an image is formed on the other side of the sheet through the process similar to that of the one-side image forming process described above. 
   An internal unit  101  is a tandem type serving as the image forming unit of the present invention, and a discharge unit  6  includes the discharge rollers  206 . A registration unit  7  includes the registration roller pair  23 , and a main body chassis  90  forms the apparatus main body. An internal unit  101  is provided to the main body chassis  90  in a replaceable manner. The discharge unit  6  serving as a sheet discharge portion, the registration unit  7  serving as a sheet conveying portion, and a fan duct  210  serving as an exhaust unit are mounted on the main body chassis  90  so as to be adjusted slidably in a vertical direction and a horizontal direction. 
   The internal unit  101  includes an image forming unit  10  having the above-mentioned four drum units  10   a  for four colors arranged in parallel with each other with respect to each shaft of the photosensitive drums  11 , and the laser scanner  13 . 
   Further, the internal unit  101  includes a drive unit (not shown) including the intermediate transferring belt  31 , the secondary transfer roller  35  for transferring the four color toner images formed on the intermediate transferring belt  31  onto the sheet, the fixing device  40 , and a motor for rotationally driving the photosensitive drums  11 , the transferring belt  31 , and the fixing device  40 . 
   Further, the internal unit  101  includes a hopper (not shown) for supplying toner to the developing device  14  and toner bottles  77 , a cleaning unit (not shown) for cleaning and collecting toner remaining on the surface of the intermediate transferring belt  31 , and a toner collecting device. 
   Further, the internal unit  101  includes a fixing entrance guide (not shown) for guiding the sheet from the secondary transfer roller  35  to the fixing device  40 , a transfer entrance guide  75  forming an entrance of a transfer path  76  through which the sheet passes after passing through the registration roller pair  23 , and a printer support casing  80  for supporting these members. 
   In this case, as illustrated in  FIG. 2 , in the fixing device  40 , which forms an upper surface of the printer support casing  80  of the internal unit  101 , a positioning hole  101   a  is formed, and two protrusions  81   a  and  81   b  are formed on a bottom surface of the printer support casing  80 . In addition, two positioning holes  101   c  are formed on a bottom surface of the transfer entrance guide  75 . One of the positioning holes  101   c  is not illustrated. 
   Further, in a lower part of the main body chassis  90 , rails  91   a  and  91   b  serving as guide units arranged in parallel with each other are provided. The rails  91   a  and  91   b  are formed by coupling two or three stages of metal rails to each other in an expandable manner. 
   Fitting holes (not shown) formed in the rails  91   a  and  91   b  are fitted with the protrusions  81   a  and  81   b  formed on the bottom surface of the printer support casing  80 , thereby making it possible to accommodate the internal unit  101  in the main body chassis  90  in a drawable manner while the internal unit  101  is moved horizontally. When the internal unit  101  is removed, the internal unit  101  together with the rails  91   a  and  91   b  are drawn out from the main body chassis  90 , and then the fitting with the rails  91   a  and  91   b  is released. 
   In this case, as illustrated in  FIG. 3 , at rear ends of the rails  91   a  and  91   b  on a side of a drawing-out direction, a removal-preventive protrusion  91   c  is provided. In this embodiment, a sheet feed cassette  20  is mounted on the apparatus main body  2  (main body chassis  90 ) in a drawing-out direction of the internal unit  101  in a drawable manner. 
   When the sheet feed cassette  20  is mounted to the apparatus main body  2 , the removal-preventive protrusion  91   c  is engaged with a rear end engaging protrusion  20   a , thereby preventing the rails  91   a  and  91   b  from being removed. Thus, the rails  91   a  and  91   b  cannot be drawn out unless the sheet feed cassette  20  is drawn out. In other words, in order to draw out the internal unit  101 , it is necessary to draw out the sheet feed cassette  20 . 
   At tip ends of the rails  91   a  and  91   b  on a downstream side of the drawing-out direction, there is provided a support portion  91   d  which is brought into contact with a handle  20   b  of the sheet feed cassette  20  when the rails  91   a  and  91   b  are drawn out together with the internal unit  101  after the sheet feed cassette  20  is drawn out. When the rails  91   a  and  91   b  are drawn out, the support portion  91   d  is brought into contact with the rails  91   a  and  91   b  by the sheet feed cassette  20  from a lower part thereof, thereby making it possible to support the rails  91   a  and  91   b  by the sheet feed cassette  20  from the lower part thereof. As s result, the internal unit  101  can be replaced and mounted in a state where the rails  91  and  91   b  are stabilized. 
   When the internal unit  101  is accommodated in the main body chassis  90 , the rails  91   a  and  91   b  are moved along with the internal unit  101  while the rails  91   a  and  91   b  are slid in a state where the internal unit  10  is drawn out. At this time, the support portion  91   d  is moved out of the way of the sliding of the rails against a spring  91   e.    
     FIG. 4  is a perspective view of the sheet discharge unit  6  provided in the main body chassis, and  FIG. 5  is an explanatory diagram of the structure of the sheet discharge unit  6 . The sheet discharge unit  6  serving as a sheet discharge portion includes a housing  207  serving as a first adjustment portion, a discharge roller pair  206 , a discharge conveying path  201  serving as a sheet discharge path, and a duplex conveying path  70 . 
   In this case, guide members  201   d  and  201   e  forming the discharge conveying path  201  are movable in a horizontal direction with respect to the housing  207  through two long holes  201   a  and  201   b  that are provided in the housing  207  and extend in the horizontal direction. Further, guide members  70   d  and  70   e  forming the duplex conveying path  70  are also movable in the horizontal direction with respect to the housing  207  through two long holes  201   a  and  201   b  that are provided in the housing  207  and extend in the horizontal direction. 
   Shafts  70   f  and  70   g  illustrated in  FIG. 5  are respectively provided to the guide members  70   d  and  70   e  forming the duplex conveying path  70 . The shafts  70   f  and  70   g  are inserted in the long holes  70   a  and  70   b , respectively, thereby making it possible to move the guide members  70   d  and  70   e  (duplex conveying path  70 ) in the horizontal direction. Shafts  201   f  and  201   g  are respectively provided to the guide members  201   d  and  201   e  forming the discharge conveying path  201 . The shafts  201   f  and  201   g  are inserted in the long holes  201   a  and  201   b , respectively, thereby making it possible to move the guide members  201   d  and  201   e  (discharge conveying path  201 ) in the horizontal direction. 
   On the other hand, the housing  207  is provided with long holes  207   a  and  207   b  extending in the vertical direction. The long holes  207   a  and  207   b  are engaged with engaging portions (not shown) provided in the main body chassis  90 , thereby making it possible to move the housing  207  in a vertical direction with respect to the main body chassis  90 . Specifically, the long holes  207   a  and  207   b  are engaged with the engaging portions provided in the main body chassis  90 , thereby making it possible to move the duplex conveying path  70  and the discharge conveying path  201  in the vertical direction together with the housing  207 . 
   Thus, the duplex conveying path  70  and the discharge conveying path  201  are provided to the housing  207  having the long holes  70   a ,  70   b ,  201   a ,  201   b ,  207   a , and  207   b , thereby making it possible to move the duplex conveying path  70  and the discharge conveying path  201  in the vertical and horizontal directions. 
   On a lower surface of the housing  207 , there are provided an opening portion  201   c  for guiding a sheet conveyed from the fixing device  40  into the discharge roller pair  206 , and an opening portion  70   c  for sending out the sheet to a conveying path  73  (see  FIG. 2 ). Further, on the lower surface of the housing  207 , there is formed a positioning protrusion  207   c  which is fitted into the positioning hole  101   a  (see  FIG. 2 ) formed in an upper part of the internal unit  101 , and positions the discharge unit  6 . 
   In a case of replacing the internal unit  101  or accommodating an internal unit  102  having another structure illustrate in  FIG. 10  to be described later in placed of the internal unit  101 , the internal unit  101  is first removed. Next, before the internal unit  101  or the internal unit  102  having another structure (hereinafter, referred to as “internal unit  101  or the like”) is accommodated in the main body chassis  90 , the discharge unit  6  (housing  207 ) is evacuated upward along the long holes  207   a  and  207   b.    
   Then, after the internal unit  101  are accommodated in the main body chassis  90 , the duplex conveying path  70  and the discharge conveying path  201  are moved along the long holes  70   a ,  70   b ,  201   a , and  201   b  to a position facing the fixing device  40  and the conveying path  73  of the internal unit  101 . After that, the positioning protrusion  207   c  is fitted into the positioning hole  101   a  of the internal unit  101 . 
   Thus, the positioning of the discharge unit  6  in the vertical and horizontal directions with respect to the internal unit  101  or the like is made. As a result, the opening portion  201   c  of the discharge conveying path  201  and the opening portion  70   c  of the duplex conveying path  70  are engaged with an outlet of the fixing device  40  and the conveying path  73  of the internal unit  101 , respectively, so as to be fixed to each other. In this embodiment, the opening portion  201   c  of the discharge conveying path  201  and the opening portion  70   c  of the duplex conveying path  70  each function as a sheet conveying interface with respect to the internal unit  101 . 
   In  FIG. 5 , a pair of upper and lower extension guides  203  correct a gap between the discharge roller pair  206  and the conveying paths which is generated due to movements of the discharge conveying path  201  and the duplex conveying path  70  in the horizontal direction. The extension guides  203  are provided in a rotatable manner in the vertical direction with rotary shafts  203   a  and  203   b  being pivots, and are brought into press contact with an lower surface of an upper end of the guide member  201   d  of the discharge conveying path  201  and an upper surface of the upper end of the guide member  70   e  of the duplex conveying path  70  by a spring  204 . 
     FIG. 6  is a perspective view for explaining the structure of the registration unit  7  serving as the sheet conveying portion provided in the main body chassis  90 . The registration unit  7  is provided to a bottom portion of the main body chassis  90 , and is positioned between the sheet feed cassette  20  provided to a lower part of the main body chassis  90  and the internal unit  10 . 
   The registration unit  7  includes a housing  222  serving as a second adjustment portion, the registration roller pair  23 , a registration guide  224 , and a side plate  225  for supporting both ends of the registration roller pair  23  and the registration guide  224 . The side plate  225  including the registration guide  224  and the registration roller pair  23  that form a sheet conveying path for conveying the sheet to the image forming unit  10  is movable in the horizontal direction with respect to the housing  222  through a slide long hole  225   a  extending in the horizontal direction. 
   Further, the housing  222  is movable in the vertical direction with respect to the main body chassis  90  through a slide long hole  222   a  extending in the vertical direction. The side plate  225  is provided to the housing  222  having the slide long holes  225   a  and  222   a  in the manner as described above, thereby making it possible to move the registration guide  224  and the registration roller pair  23  in the vertical and horizontal directions. 
   On an upper surface of the side plate  225 , there is formed a positioning protrusion  225   b  for positioning the registration unit  7  while being fitted into the above-mentioned positioning hole  101   c  (see  FIG. 2 ) formed in the upper part of the internal unit  101 . The positioning protrusion  225   b  is also provided to a side plate (not shown) positioned on an opposite side of a longitudinal direction. 
   In the case where the internal unit  101  is replaced or in the case where another internal unit is accommodated in the main body chassis in place of the internal unit  101 , the internal unit  101  is first removed. Next, before the internal unit  101  is accommodated in the main body chassis  90 , the registration unit  7  (housing  222 ) is slid and evacuated downward along the slide long hole  222   a.    
   Then, after the internal unit  101  or the like is accommodated in the main body chassis  90 , the housing  222  is moved upward along the slide long hole  222   a . In addition, the registration guide  224  and the registration roller pair  23  are moved integrally with the side plate  225  to the position facing the transfer path  76  (see  FIG. 2 ) of the internal unit  101 . After that, the positioning protrusion  225   b  is fitted into the positioning hole  101   c  of the internal unit  101 . 
   Thus, the positioning of the registration unit  7  in the vertical and horizontal directions with respect to the internal unit  101  is made. As a result, the registration guide  224  and the registration roller pair  23  of the registration unit  7  are fixed to the position facing the transfer path  76  of the internal unit  101 . When the registration unit  7  is positioned to the internal unit  101  to be mounted in the manner as described above, the registration roller pair  23  functions as a sheet conveying interface with respect to the internal unit  101 . 
     FIG. 7  is a perspective view of the fan duct  210  which serves as an exhaust unit and is provided on a back surface in an electric housing  93  of the main body chassis  90 , and  FIG. 8  is an explanatory diagram of a structure of the fan duct  210 . 
   In  FIGS. 7 and 8 , a fan  211  is mounted to the electric housing  93  so as to face opening portions  92  having slits provided in an external cover  92  on a back surface of the apparatus main body. At four corners of the fan  211 , four wires  217  which are elastically deformable are provided, and a first fixing plate  214  is provided at tip ends of the wires  217  in a movable manner along with the wires  217 . 
   At the center portion of the first fixing plate  214 , an exhaust port  214   a  serving as an opening portion functioning as an inlet for an air duct is formed. In this embodiment, the exhaust duct  216  is formed by covering the four wires  217  with a cloth, rubber, or elastic resin, thereby preventing air leakage from the first fixing plate  214  to the fan  211 . 
   In this case, the first fixing plate  214  is movable in the vertical direction with respect to a second fixing plate  215 , which serves as a third adjustment portion and is mounted on the electric housing  93  as illustrated in  FIG. 9 , along long holes  215   a  which are formed in the second fixing plate  215  and extend in the vertical direction. Further, the first fixing plate  214  is fixed to the second fixing plate  215  with screws  212 . 
   The second fixing plate  215  having the long holes  215   b  extending in the horizontal direction is movable in the horizontal direction with respect to the electric housing  93  along the long holes  215   b , and can be fixed to an arbitrary position of the electric housing  93  with the screws  212 . Further, the second fixing plate  215  also has an opening portion  215   c  in the same manner as the first fixing plate  214 , and the electric housing  93  also has an opening portion. Thus, the airflow from the fan  211  to the main body chassis  90  is assured. 
   Thus, the first fixing plate  214  having the opening portion  214   a  is mounted to the second fixing plate  215  having the long holes  215   a  and  215   b , thereby making it possible to move the exhaust port  214   a  in the vertical and horizontal directions. 
   In the case where the internal unit  101  is replaced, or in the case where another internal unit is accommodated in the main body chassis in place of the internal unit  101 , the internal unit  101  is first removed. Next, before the internal unit  101  is accommodated in the main body chassis  90 , the first fixing plate  214  is moved in the vertical direction along the long holes  215   a . Further, the second fixing plate  215  is moved in the vertical direction along the long holes  215   b.    
   After that, the two fixing plates  214  and  215  are fixed to positions appropriate for exhausting heat generated from the internal unit  101 . As a result, it is possible to move the exhaust port  214   a  to the position facing the internal unit  101 . Another opening portion may be provided in the exhaust duct  210  to thereby exhaust heat within the electric housing  93 . 
     FIG. 10  shows a structure of a rotary internal unit serving as another structure of an image forming unit which can be mounted on the color printer  1  having the above-mentioned structure. In  FIG. 10 , components identical with or corresponding to those of  FIG. 2  are denoted by the same reference symbols. 
   In this case, another rotary internal unit  102  includes the image forming unit  10  having a structure different from that of a tandem internal unit  101  illustrated in  FIG. 2 . A position appropriate for the sheet to enter the image forming unit  10  of the rotary internal unit is different from that of the tandem internal unit  10 . Further, the position of the fixing device  40  of the rotary internal unit is different from that of the tandem internal unit  10 . As a result, a position from which the sheet is delivered, a heat source, heat capacity, and an internal airflow (gap through which air flows) are different between the rotary internal unit and the tandem internal unit, thereby varying a position of the fan duct appropriate for exhausting heat. 
   Another internal unit  102  has the positioning protrusions  81   a  and  81   b  and the positioning holes  101   a  and  101   c  at the same positions as those of the tandem internal unit  101 . 
   Next, a method of replacing the tandem internal unit  101  with another internal unit  102  will be described. 
   First, the tandem internal unit  101  is removed from the main body chassis  90 . In this case, the multi-feed tray  25  is removed first, and then connection between the discharge conveying path  201  and the fixing device  40  is released while the discharge unit  6  is moved upward. Further, connection between the discharge conveying path  201  and the transfer entrance guide  75  is released. Since the fan duct  210  includes no connecting unit with respect to the internal unit  101 , there is no need to release connection. 
   Next, after the sheet feed cassette  20  is drawn out in a front-right direction of  FIG. 2 , the internal unit  101  is drawn out together with the rails  91 . After that, fitting of the internal unit  101  with the rails  91  is released, and the internal unit  101  is removed from the main body chassis  90 . 
   Then, another internal unit  102  is mounted on the rails  90  while the positioning protrusions  81  and  81   b  are fitted to the rails  90 , respectively, and then another internal unit  102  is accommodated in the main body chassis  90  together with the rails  91 . At this time, the discharge unit  6  is evacuated in advance to evacuate the registration unit  7  downward. The multi-feed tray  25  is removed in advance. 
   Then, the positioning protrusion  207   c  (see  FIG. 4 ) of the discharge unit  6  is fitted into the positioning holes  101   a  formed on both sides of the upper portion of the fixing device  40  of another internal unit  102 , thereby positioning the discharge unit  6  in a back and forth, vertical, and horizontal directions to be fixed. 
   Then, the positioning protrusion  225   b  (see  FIG. 6 ) of the registration unit  7  is fitted into the positioning hole  101   c  provided in the vicinity of the transfer entrance guide  75  of another internal unit  102  to fix the registration unit  7 . Then, the multi-feed tray  25  is mounted to a side of another internal unit  102  and the feed cassette  20  is mounted on the main body chassis  90 . 
   The fan duct  210  selects the position appropriate for exhausting heat of another internal unit  102  to move the first and second fixing plates  214  and  215 , fixing the exhaust port  214   a  to the position appropriate for exhausting heat (exhaust) which is adjacent to the internal unit  101 . As a result, another internal unit  102  is accommodated in the main body chassis  90  without being restricted in a difference between the positions of the discharge unit  6  and the registration unit  7 . 
   Thus, when the internal unit is replaced, the positions of the discharge unit  6  and the registration unit  7  with respect to another internal unit  102  to be replaced are adjusted, thereby making it possible to selectively accommodate the internal unit  102 , which includes the image forming units having the different structures, in the apparatus main body. As a result, even when the structure of the image forming unit  10  is varied, the respective positions of the discharge unit  6 , the registration unit  7 , and the fan duct  210  are arbitrarily set, thereby making it possible to commonly use the apparatus main body  2  (main body chassis  90 ). 
   With the structure described above, various image forming units (image forming units) adopting different image forming processes (structures) can be mounted on one main body chassis (apparatus main body). As a result, it is possible to reuse or commonly use the apparatus main body, and thereby achieve reduction in manufacturing costs. Further, also in a case of recycling the image forming apparatus, the image forming unit can be easily removed, thereby making it possible to reduce recycling costs and further easily make one image forming apparatus into another image forming apparatus adopting a different image forming process. 
   In the above description, the color printer using the intermediate transferring belt is described, but the present invention is not limited thereto. The present invention can be applied to, for example, a color printer which does not use the intermediate transferring belt, a color electrophotographic printer including one image bearing member, for example, a photosensitive drum, and also a monochromatic printer. 
   In this embodiment, the structure in which position adjustment is performed through the long hole when the discharge unit  6  and the registration unit  7  are mounted to the internal units  101  and  102  is described as an example, but the present invention is not limited thereto. For example, the position adjustment may be performed by forming a plurality of positioning holes and selectively using the holes. Further, the position adjustment may be performed also by using both the long hole and the positioning hole. 
   While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
   This application claims the benefit of Japanese Patent Application No. 2006-093633, filed Mar. 30, 2006, which is hereby incorporated by reference herein in its entirety.