Patent Publication Number: US-7593667-B2

Title: Image forming apparatus with detachable process unit

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority from Japanese Patent Application No. 2005-050917, filed on Feb. 25, 2005, the entire subject matter of which is incorporated herein by reference. 
   1. Technical Field 
   Aspects of the present invention relate to an image forming apparatus in which a unit accommodation section that accommodates a process unit is formed so as to have an opening. 
   2. Background 
   In image forming apparatus such as laser printers and copiers, expendables such as a photosensitive drum and a developer used therein need to be replaceable. In view of this, conventionally, many kinds of image forming apparatus have been developed that are configured in such a manner that a process unit as a unitized implementation of a photosensitive drum, a developer accommodation room, etc., can be attached to and detached from an apparatus main body of the image forming apparatus. More specifically, a unit accommodation section capable of accommodating a process unit is formed in the apparatus main body so as to have an opening in one wall of the apparatus main body, and a cover for closing the opening is provided so as to be openable. However, this configuration has a problem that replacement of the process unit takes time and labor because an operation of opening the cover and an operation of pulling out the process unit need to be performed independently. 
   JP-A-2004-302009 discloses a configuration in which a sheet material accommodation member which accommodates sheet materials and which is movable with respect to the apparatus main body is provided integrally with the above-mentioned cover. In this configuration, the opening of the unit accommodation section is also opened when the sheet material accommodation member is pulled out to supply sheet materials to it. This allows process unit replacement work to be performed easily at the same time. 
   SUMMARY 
   However, in the configuration disclosed in JP-A-2004-302009, an operation of pulling out the sheet material accommodation member is necessary even in the case of replacing only the process unit. Undue time and labor are required after all. 
   The present invention provides an image forming apparatus in which an operation of pulling out a process unit can be performed easily. 
   According to an aspect of the invention, there is provided an image forming apparatus including: a process unit having a developer container for containing a developer; an apparatus main body having an opening and a unit accommodation section into which the process unit is inserted through the opening and detachably accommodated; and a cover for closing the opening in a state that the process unit is accommodated in the unit accommodation section, the cover being integrally provided with the process unit. 
   In the invention, the image forming apparatus is not limited to a printing apparatus such as a printer (e.g., laser printer) and may be a facsimile machine or a multi-function machine having a printer function, a scanner function, etc. 
   The process unit is only required to be able to be pulled out of the apparatus main body and maybe such as not to be separated 
   In this configuration, the cover for closing the opening of the unit accommodation section is provided integrally with the process unit. Therefore, the process unit can be pulled out of the unit accommodation section together with the cover by opening the cover to let the opening appear. The efficiency of the operation of pulling out the process unit can thus be increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative aspects of the invention may be more readily described with reference to the accompanying drawings: 
       FIG. 1  is a side sectional view of a laser printer according to a first aspect of the present invention (a state that attachment of a process unit has completed); 
       FIG. 2  is a side sectional view of the laser printer (a state that the process unit is pulled out); 
       FIG. 3  is an enlarged side sectional view of the process unit; 
       FIG. 4  is a perspective view showing a state that a drive gear on a process unit side is engaged with drive gears on an apparatus main body side; 
       FIG. 5  is a perspective view showing a state that the drive gear on the process unit side is disengaged from the drive gears on the apparatus main body side; 
       FIG. 6  is an enlarged side sectional view of a process unit according to a second aspect; and 
       FIG. 7  is an enlarged side sectional view of a process unit according to a third aspect. 
   

   DETAILED DESCRIPTION 
   &lt;Aspect 1&gt; 
   A first aspect of the present invention will be described below with reference to  FIGS. 1-5 . 
   1. Total Configuration of Aspect 
     FIG. 1  is a side sectional view of a laser printer  1  as an image forming apparatus according to the aspect of the invention.  FIG. 2  is a side sectional view of the laser printer  1  in a state that a process unit  15  is pulled out of an apparatus main body of the laser printer  1 . In the following description, that wall of the laser printer  1  through which to pull out the process unit  15  (i.e., the right-hand wall in the paper surface of  FIG. 2 ) will be referred to as “front wall (or surface).” 
   As shown in  FIGS. 1 and 2 , the laser printer  1  is equipped with, in a main body casing  2 , a feeder unit  4  for supplying a sheet (sheet material)  3 , an image forming section  5  for forming a prescribed image on the sheet  3  supplied, and other units and components. The main body casing  2  is formed with a unit accommodation section  2   b  which communicates with an opening  2   a  formed in the front wall of the main body casing  2 . The process unit  15  can be inserted into the unit accommodation section  2   b  through the opening  2   a  and accommodated therein detachably. In this aspect, that part of the laser printer  1  which excludes the process unit  15  functions as an “apparatus main body” and will be called “apparatus main body  1   a ” below. 
   (1) Configuration of Feeder Unit 
   The feeder unit  4  is equipped with a sheet supply cassette  7  which can accommodate sheets  3  and is attached to a bottom portion of the main body casing  2  detachably, a sheet pressing plate  6  which is provided inside the sheet supply cassette  7 , a sheet feed roller  8  and a sheet feed pad  9  which are disposed above one end portion of the sheet supply cassette  7 , a pair of counter rollers  10  which are disposed downstream of the sheet feed pad  9  in the sheet transport direction of the sheet  3  so as to be opposed to the sheet feed roller  8 , and registration rollers  11  which are disposed downstream of the counter rollers  10  in the sheet transport direction of the sheet  3 . 
   The sheet pressing plate  6  is configured so that sheets  3  can be stacked thereon. Its end portion that is more distant from the sheet feed roller  8  (i.e., on the side of the rear surface of the laser printer  1 ) is supported swingably, and its end portion that is closer to the sheet feed roller  8  (i.e., on the side of the front surface of the laser printer  1 ) can be rotated in the vertical direction. The sheet pressing plate  6  is urged upward by a spring (not shown) from its back side. Therefore, as the number of stacked sheets  3  increases, the sheet pressing plate  6  rotates downward against the urging force of the spring with its rear-surface-side end portion with respect to the sheet feed roller  8  as a supporting point. The sheet feed roller  8  and the sheet feed pad  9  are opposed to each other, and the sheet feed pad  9  is pressed against the sheet feed roller  8  by a spring (not shown) which is disposed on the back side of the sheet feed pad  9 . 
   Top sheets  3  on the sheet pressing plate  6  are pressed against the sheet feed roller  8  by the spring (not shown) from the back side of the sheet pressing plate  6 , held between the sheet feed roller  8  and the sheet feed pad  9  by rotation of the sheet feed roller  8 , and then sent out one by one. A sheet  3  thus sent out is reversed in the traveling direction (from the forward direction to the rearward direction of the laser printer  1 ) while being guided by the sheet feed roller  8 , the counter rollers  10 , etc., and the sheet  3  is sent to the registration rollers  11 . The registration rollers  11  are a pair of rollers, that is, a drive roller  12  which is provided on the main body casing  2  side and a follower roller  13  which is provided on the process unit  15  side. The sheet  3  sent from the counter rollers  10  is nipped by the drive roller  12  and the follower roller  13 , subjected to prescribed registration, and then sent to the image forming section  5 . 
   (2) Configuration of Image Forming Section 
   The image forming section  5  is equipped with a scanner unit  14 , the process unit  15 , a fixing unit  16 , etc. 
   (a) Configuration of Scanner Unit 
   The scanner unit  14  is disposed above the unit accommodation section  2   b  of the main body casing  2 , and is equipped with a laser light emitting section (not shown), a polygon mirror  17  which is driven rotationally, a lens  18 , a reflector  19 , etc. As indicated by a broken line, a laser beam emitted from the laser light emitting section according to prescribed image data passes through or is reflected by the polygon mirror  17 , the lens  18 , the reflector  19 , etc. in order, and is finally applied to the surface of a photosensitive drum  20  of the process unit  15  (described later) to scan it at high speed. 
   (b) Configuration of Process Unit 
     FIG. 3  is an enlarged side sectional view of the process unit  15 . As shown in the figure, the process unit  15  is configured in such a manner that a drum cartridge  22  and a development cartridge  23  are provided on a base cartridge  21  detachably. 
   Among those cartridges, the development cartridge  23  is equipped with a toner box  24 , a layer thickness limiting blade  25 , a supply roller  26 , and a development roller  27 , etc. A positively chargeable, non-magnetic mono-component toner as a developer is charged in the toner box  24 . The toner in the toner box  24  is agitated by an agitator  29  which is provided rotatably at the center of the toner box  24 , and toner is discharged through a toner supply opening  30  which is formed behind the toner box  24 . 
   The supply roller  26  is disposed rotatably below the toner supply opening  30 , and the development roller  27  is disposed rotatably so as to be opposed to the supply roller  26 . The supply roller  26  and the development roller  27  are in contact with each other so as to compress each other to a certain extent. 
   The supply roller  26  is configured in such a manner that a metal roller shaft is covered with a roller made of a conductive foamed material. The development roller  27  is configured in such a manner that a metal roller shaft is covered with a roller made of a conductive rubber material. More specifically, the roller portion of the development roller  27  is configured in such a manner that the surface of a roller main body made of conductive urethane rubber or silicone rubber containing carbon fine particles etc. is covered with a coat layer made of urethane rubber or silicone rubber containing fluorine. A prescribed development bias, with respect to the potential of the photosensitive drum  20 , is applied to the development roller  27 . 
   The layer thickness limiting blade  25  is disposed in the vicinity of the development roller  27 . The layer thickness limiting blade  25  is provided with a blade main body  37  which is a metal leaf spring member and a pressing portion  38  which is provided at the tip of the blade main body  37 , is made of insulative silicone rubber, and has a semicircular cross section. The end portion, opposite to the pressing portion  38 , of the blade main body  37  is supported by the development cartridge  36  at a position close to the development roller  27 , and the pressing portion  38  is brought in pressure contact with the development roller  27  by the elastic force of the blade main body  37 . 
   Toner that is discharged through the toner supply opening  30  is supplied to the development roller  27  by rotation of the supply roller  26 . During that course, the toner is charged positively by friction between the supply roller  26  and the development roller  27 . The toner that has been supplied onto the development roller  27  goes into the boundary between the layer thickness limiting blade  25  and the development roller  27  and is further charged there by friction as the development roller  27  is rotated. As a result, the toner comes to be carried by the development roller  27  as a thin layer having a constant thickness. 
   Next, the drum cartridge  22  is equipped with the photosensitive drum  20 , a scorotron charger  28 , etc. 
   As shown in  FIG. 1 , the photosensitive drum  20  is disposed rotatably behind the development roller  27  so as to be opposed to the development roller  27 . In the photosensitive drum  20 , a drum main body is grounded and its surface portion is a positively chargeable photoreceptor layer made of polycarbonate or the like. 
   The scorotron charger  28  is disposed above the photosensitive drum  20  with a prescribed interval so as to avoid contact with the photosensitive drum  20 . The scorotron charger  28  is a positively charging one in which corona discharge occurs from a charging wire made of tungsten or the like. The scorotron charger  28  is configured so as to charge the surface of the photosensitive drum  20  positively and uniformly. 
   After being charged positively and uniformly by the scorotron charger  28 , the surface of the photosensitive drum  20  is exposed to a laser beam coming from the scanner unit  14  (i.e., subjected to a high-speed scan), whereby an electrostatic latent image according to prescribed image data is formed. Then, as the development roller  27  is rotated, toner that is carried by the development roller  27  and charged positively is supplied to the electrostatic latent image, that is, the exposed portions (where the potential has been lowered by the exposure to the laser beam) of the surface of the photosensitive drum  20  (which was charged positively and uniformly), in a state that the development roller  27  is opposed to and is in contact with the photosensitive drum  20  and the toner comes to be carried selectively by the photosensitive drum  20 . As a result, the electrostatic latent image is visualized and development is thus completed. 
   As shown in  FIG. 1 , a transfer roller  31  is disposed rotatably under the bottom surface of the unit accommodation section  2   b  so as to be opposed to the photosensitive drum  20 . The visible image is transferred to a sheet  3  that has been transported by the registration rollers  11  as the sheet  3  is nipped by the photosensitive drum  20  and the transfer roller  31 . 
   (c) Configuration of Fixing Unit 
   As shown in  FIGS. 1 and 2 , the fixing unit  16  is disposed downstream of the process unit  15  in the sheet transport direction of the sheet  3  and is equipped with a heating roller  32  and a pressing roller  33  which is pressed against the heating roller  32 . The heating roller  32  is made of a metal and equipped with a halogen lamp for heating. Toner that has been transferred to a sheet  3  is thermally fused in the process unit  15  while the sheet  3  passes between the heating roller  32  and the pressing roller  33 , and transports the sheet  3  to a sheet ejection path  34 . The sheet  3  that has been transported to the sheet ejection path  34  is ejected onto a sheet ejection tray  36  by a pair of sheet ejection rollers  35 . 
   2. Specific Configuration of Process Unit 
   As shown in  FIG. 3 , the base cartridge  21  is equipped with a first mounting portion  21   a  which is located close to the rear end of the base cartridge  21 , has a top opening, and is to receive the drum cartridge  22  detachably. The base cartridge  21  is also equipped with a second mounting portion  21   b  which is located in front of the first mounting portion  21   a , also has a top opening, and is to receive the development cartridge  36  detachably. The first mounting portion  21   a  has an accommodation space that conforms to the shape of the drum cartridge  22 . Cuts as bearing portions  37  (only the left-hand one is shown in the figure) are formed in the right and left side walls, respectively, and end portions of the roller shaft of the photosensitive drum  20  are inserted into the respective bearing portions  37 , whereby the drum cartridge  22  is positioned with respect to the base cartridge  21 . A through-hole  38  for exposing the bottom surface of the photosensitive drum  20  in a state that the drum cartridge  22  is mounted is formed through the bottom wall of the first mounting portion  21   a . The photosensitive drum  20  and the transfer roller  31  are opposed to each other through the through-hole  38  so as to form a nip position. 
   On the other hand, the second mounting section  21   b  has an accommodation space that conforms to the shape of the development cartridge  23 . For example, the development cartridge  23  is positioned with respect to the base cartridge  21  by an engaging portion (not shown). As shown in  FIGS. 1-3 , an engagement portion  22   a  which is located at the front end of the drum cartridge  22  is engaged with an engagement subject portion  23   a  which is located at the rear end of the development cartridge  23 , whereby the development roller  27  and the photosensitive drum  20  are opposed to each other in a regular state and prevented from deviating from such positions. 
   As shown in  FIG. 1 , a cover  39  for closing the opening  2   a  of the main body casing  2  in a state that the process unit  15  is inserted in the unit accommodation section  2   b  is provided integrally with the base cartridge  21  at the front end of the base cartridge  21 . The cover  39  is formed with a handle  40  at a bottom-front position, and the base cartridge  21  can be pulled out of the apparatus main body  1   a  by gripping the handle  40 . A sheet insertion hole  41  extending in the right-left direction is formed through the front wall of the base cartridge  21  above the handle  40 . A sheet  3  can be inserted through the sheet insertion hole  41  manually, for example. A sheet  3  inserted through the sheet insertion hole  41  is likewise transported to the registration rollers  11  by the sheet feed roller  8  and subjected to image formation by the image forming section  5 . 
   Further, the base cartridge  21  is provided with the above-mentioned sheet feed roller  8  and counter rollers  10  at a the bottom-front position, more specifically, behind the sheet insertion hole  41 . That is, the sheet feed roller  8  and the counter rollers  10  are pulled out of the apparatus main body  1   a  together with the process unit  15 . This structure is effective in miniaturizing the laser printer  1  in the vertical direction while enabling attachment/detachment of the process unit  15 . More specifically, as shown in  FIG. 1 , the height Y of the bottom surface of the photosensitive drum  20  is set lower than the height X of the top surface of the sheet feed roller  8  in a state that the process unit  15  is inserted completely, whereby the process unit  15  is located at as low a position as possible and the vertical size of the laser printer  1  is thereby reduced. Since the sheet feed roller  8  and the counter rollers  10  are pulled out of the apparatus main body  1   a  together with the process unit  15 , the process unit  15  can be attached and detached smoothly (see  FIGS. 1 and 2 ). 
   3. Engagement/Disengagement of Gears when the Process Unit is Attached or Detached 
     FIGS. 4 and 5  are perspective views showing the process unit  15  and a gear mechanism for driving the sheet feed roller  8  etc. rotationally. 
   As shown in the figures, a roller shaft end portion  8   a  of the sheet feed roller  8  projects on the right side of the process unit  15  and the tip portion of the roller shaft end portion  8   a  is fitted in an input gear  50  which rotates together with the roller shaft end portion  8   a . On the other hand, the apparatus main body  1   a  is equipped with a driving motor  51  and a main-body-side gear mechanism  52  which is driven rotationally receiving drive power from the driving motor  51 . As shown in  FIG. 4 , an output gear  53  which is located at the front end of the main-body-side gear mechanism  52  is engaged with the input gear  50 , whereby drive power is transmitted from the driving motor  51  to the roller shaft end portion  8   a  and the sheet feed roller  8  is driven rotationally. 
   Therefore, when the process unit  15  is pulled out of the apparatus main body  1   a  (see  FIG. 2 ), the output gear  53  is disengaged from the input gear  50  and the sheet feed roller  8  is rendered free. The main-body-side gear mechanism  52  includes a gear  54  for driving the photosensitive drum  20  rotationally, a gear  55  for driving the development roller  27  rotationally, etc. 
   4. Advantages of Aspect 
   (1) In the aspect, the cover  39  for closing the opening  2   a  of the main body casing  2  is provided integrally with the process unit  15 . Therefore, the process unit  15  can be taken out together with the cover  39  by pulling out the process unit  15  by gripping the handle  40  which is attached to the process unit  15 . 
   (2) In the process unit  15 , the drum cartridge  22  and the development cartridge  23  can be attached to and detached from the base cartridge  21  individually. Therefore, if, for example, toner replacement is necessary because the toner has been used up or has deteriorated, the process unit  15  can be inserted into the apparatus main body  1   a  again after replacing only the development cartridge  23 . If, for example, the photosensitive drum  20  has been damaged and requires replacement, it is sufficient to replace only the drum cartridge  22 . 
   (3) Further, such a transport unit as the sheet feed roller  8  which may become obstacles in a process of attaching or detaching the process unit  15  are attached to the process unit  15  and pulled out of the apparatus main body  1   a  together with the process unit  15 . Therefore, as described above, the vertical size of the laser printer  1  can be miniaturized. 
   (4) Still further, when the process unit  15  is pulled out, the input gear  50  which rotates together with the sheet feed roller  8  is disengaged from the output gear  53  (which is provided on the apparatus main body  1   a ) and is thereby rendered free. Therefore, even if a jam of a sheet  3  has occurred in the sheet transport path along part of the circumferential surface of the sheet feed roller  8 , the jammed sheet  3  can be removed easily by making the sheet feed roller  8  free by pulling out the process unit  15 . 
   &lt;Aspect 2&gt; 
     FIG. 6  shows a second aspect. This aspect is the same as the first aspect except for the configuration of the process unit. Therefore, units and components having the same ones in the first aspect will be given the same reference symbols as in the first aspect, and redundant descriptions will be omitted. Only different points will be described below. 
   As shown in  FIG. 6 , in a process unit  60  according to this aspect, the toner box  24 , the layer thickness limiting blade  25 , the supply roller  26 , and the development roller  27  are provided integrally with a base cartridge  61  and cannot be detached from the base cartridge  61 . 
   This configuration can increase the positioning accuracy of the process unit  60  with respect to the apparatus main body  1   a  though the supply roller  26  and the development roller  27  cannot be detached from the base cartridge  61 . 
   &lt;Aspect 3&gt; 
     FIG. 7  shows a third aspect. This aspect is the same as the first aspect except for the configuration of the process unit. Therefore, units and components having the same ones in the first aspect will be given the same reference symbols as in the first aspect, and redundant descriptions will be omitted. Only different points will be described below. 
   As shown in  FIG. 7 , in a process unit  70  according to this aspect, the photosensitive drum  20  and the scorotron charger  28  are provided integrally with a base cartridge  71  and cannot be detached from the base cartridge  71 . 
   This configuration can increase the positioning accuracy of the photosensitive drum  20  with respect to the transfer roller  31  in the side of the apparatus main body  1   a  though it cannot be detached from the base cartridge  71 . 
   &lt;Other Aspects&gt; 
   The invention is not limited to the aspects that have been described above with reference to the drawings. For example, the following aspects are also included in the technical scope of the invention. And various modifications other than the following aspects are possible without departing from the spirit and scope of the invention. 
   (1) The first aspect may be modified in such a manner that the drum cartridge  22  and the development cartridge  23  are integrated with each other so as to be attached to and detached from the base cartridge  21  together. In this case, the positional accuracy of the development roller  27  and the photosensitive drum  20  can be kept high. 
   (2) The transport unit is only required to be provided on the side of the aperture of the apparatus main body and to transport a sheet material to the process unit. That is, the transport unit need not be a means for transporting a sheet material accommodated in the sheet material accommodation unit which is disposed under the unit accommodation section, and may be, for example, a dedicated roller for transporting a sheet  3  that is inserted through the sheet insertion hole  41  in the above aspects. 
   (3) Although in the above aspects the sheet feed roller  8  is provided as a transport roller, the same purpose may be attained by a gear that rotates together with, for example, one of the counter rollers  10 , one of the registration rollers  11 , or the like as long as it is engaged with an apparatus-main-body-side drive gear. 
   As was described, according to the above-described aspect, the process unit has an image carrier accommodation unit that accommodates an image carrier, and a base unit on which the developer container and the image carrier accommodation unit are mounted, the base unit being integrally provided with the cover; and the developer container and the image carrier accommodation unit are capable of being attached to and detached from the base unit. 
   The image carrier is not limited to a photosensitive drum (photoreceptor body) and may be an intermediate transfer body. 
   The developer container and the image carrier accommodation unit may be either separate units that can be attached to and detached from the base unit independently or an integral unit (i.e., they can be attached to and detached from the base unit together). 
   Alternatively, the process unit has an image carrier accommodation unit that accommodates an image carrier, and a base unit on which the developer container and the image carrier accommodation unit are mounted, the base unit being integrally provided with the cover; and the developer container is integrally provided with the base unit and the image carrier accommodation unit is capable of being attached to and detached from the base unit. 
   Alternatively, the process unit has an image carrier accommodation unit that accommodates an image carrier, and a base unit on which the developer container and the image carrier accommodation unit are mounted, the base unit being integrally provided with the cover; and the developer container is capable of being attached to and detached from the base unit and the image carrier accommodation unit is integrally provided with the base unit. 
   In these configurations, at least one of the developer container and the image carrier accommodation unit can be attached to and detached from the base unit, which makes it possible to replace only a minimum number of components (expendables) such as the developer and the image carrier that require replacement. In general, the developer and the image carrier have different lives. Therefore, it is desirable that the developer container and the image carrier accommodation unit be able to be attached to and detached from the base unit independently. 
   In addition, the image forming apparatus further includes: a sheet material accommodation unit disposed under the unit accommodation section, for accommodating a sheet material; and a transport unit disposed on a side of the opening, for transporting the sheet material accommodated in the sheet material accommodation unit to the process unit; wherein the transport unit is supported by the process unit and is capable of being pulled out of the apparatus main body together with the process unit. 
   The sheet material includes a sheet of paper and an OHP sheet as recording media. 
   Image forming apparatus currently show a tendency of size reduction particularly in the vertical direction. Therefore, to secure a space through which to pull out the process unit, the transport means which is provided on the side of the opening may become an obstacle. In view of this, in this configuration, the transport means which may become an obstacle is also attached to the process unit and is pulled out together with the process unit. 
   Also, the transport unit has a gear mechanism that receives drive power when engaged with a drive gear provided in the apparatus main body, and a transport roller for transporting the sheet material when rotated being driven by the gear mechanism; and the gear mechanism is disengaged from the drive gear when the process unit is pulled out of the apparatus main body. 
   In addition, the image forming apparatus further includes: a separation pad and a separation roller opposed to each other, for separating sheet materials supplied from the sheet material accommodation unit into single sheet material and transporting the single sheet material one by one, the separation roller serving as the transport roller. 
   In this configuration, when the process unit is pulled out of the apparatus main body, the gear mechanism is disengaged from the drive gear and the transport roller is rendered free. This facilitates work of removing, from the transport path, a sheet that has been jammed in the middle of a transport. The separation roller and the separation pad for separating sheet materials into single ones provide particularly strong nip force. Therefore, it is particularly desirable to render the separation roller free in pulling out the process unit. 
   Moreover, a bottom surface of the image carrier is lower than a top surface of the transport roller in a state that the process unit is accommodated in the unit accommodation section. 
   In this configuration, the bottom surface of the image carrier is lower than the top surface of the transport roller, whereby the size of the image forming apparatus is reduced in the vertical direction.