Patent Publication Number: US-8967620-B2

Title: Sheet transport device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2013-008029 filed Jan. 21, 2013. 
     BACKGROUND 
     The present invention relates to a sheet transport device. 
     SUMMARY 
     According to an aspect of the invention, there is provided a sheet transport device including a device body that transports a sheet; a pair of transport rollers that come into contact with each other and transport the sheet toward a downstream side in a transport direction of the sheet; a transport member that guides and transports the sheet toward the pair of transport rollers; and an open and close member that opens and closes a side surface of the device body. One of the pair of transport rollers is provided at the device body and the other transport roller is provided at the transport member, and the transport member is rotatable around an axis that is parallel to the pair of transport rollers. When the open and close member moves to an open position at which the side surface is open, the open and close member rotates around the axis and the contact between the pair of transport rollers is allowed to be released. 
    
    
     
       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 schematic vertical section illustrating an inner configuration of an image forming apparatus. 
         FIG. 2  is a schematic section illustrating an inner configuration and sheet transportation of a sheet transport section of the image forming apparatus. 
         FIG. 3  is a schematic partial section illustrating the sheet transport section of the image forming apparatus. 
         FIGS. 4A and 4B  are schematic partial illustrations each explaining movement of a sheet transport unit by an open operation of an open and close panel. 
         FIGS. 5A to 5C  are schematic illustrations each explaining an example of a release structure of positioning engagement between an engagement protrusion and a recess. 
         FIGS. 6A to 6C  are schematic partial illustrations each explaining movement of the sheet transport unit caused by a close operation of the open and close panel. 
         FIGS. 7A and 7B  are schematic partial illustrations each explaining movement of a transfer and transport unit caused by the close operation of the open and close panel. 
         FIG. 8  is a schematic partial section illustrating a sheet transport section of an image forming apparatus. 
         FIGS. 9A and 9B  are schematic partial illustrations each explaining movement of a sheet transport unit by a close operation of an open and close panel. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments and specific examples of the invention are described below in detail with reference to the drawings. However, the invention is not limited to the exemplary embodiments or the specific examples. 
     Also, in the description with reference to the drawings, the drawings are merely schematically illustrated, and it should be noted that the ratios of illustrated dimensions may differ from the ratios of actual dimensions. Illustration of members other than members required for the description is omitted for easier understanding. 
     In the drawings, it is assumed that an X-axis direction is a front-rear direction, a Y-axis direction is a left-right direction, and a Z-axis direction is an up-down direction for easier understanding of the description. 
     First Exemplary Embodiment 
     (1) General Configuration and Operation of Image Forming Apparatus 
       FIG. 1  is a schematic vertical section illustrating an inner configuration of an image forming apparatus  1  according to this exemplary embodiment. 
     A general configuration and an operation of the image forming apparatus  1  are described below with reference to the drawings. 
     The image forming apparatus  1  includes a control unit  10 , a sheet feed unit  20 , a photoconductor unit  30 , a development unit  40 , a sheet transport unit  50 , a transfer and transport unit  60 , and fixing unit  70  in a housing  100 . An output tray portion T is formed at an upper surface (Z direction) of the image forming apparatus  1 . A sheet having an image recorded thereon is output to and housed on the output tray portion T. Further, an open and close panel  110  is rotatably supported at a rear surface (−X direction) of the image forming apparatus  1 . The open and close panel  110  opens the inside of the image forming apparatus  1 , for example, when a clogged sheet is removed or the inside is inspected. 
     The control unit  10  includes a controller  11  that controls an operation of the image forming apparatus  1 , an image processing device  12 , an operation of which is controlled by the controller  11 , and a power supply device  13 . The power supply device  13  applies voltages to, for example, a charging roller  32 , a development roller  42 , and a transfer roller  62  (described later). 
     The image processing device  12  converts print information input from an external information transmit device (for example, a personal computer) into image information for latent-image formation, and outputs a driving signal to an exposure device LH at a predetermined timing. The exposure device LH of this exemplary embodiment is formed of an LED head having light emitting diodes (LEDs) arranged in a linear form. 
     The sheet feed unit  20  is provided in a bottom portion of the image forming apparatus  1 . The sheet feed unit  20  includes a sheet stack plate  21 . Multiple sheets serving as recording media are stacked on an upper surface of the sheet stack plate  21 . The sheets, which are stacked on the sheet stack plate  21  and positioned in a width direction by a regulation plate (not illustrated), are drawn one by one from the upper side to the front side (−X direction) by a sheet draw portion  22 . Then, the drawn sheet passes through a sheet guide  23  serving as a first transport unit fixed in the housing  100  and a sheet guide  51  serving as a second transport unit formed at the sheet transport unit  50 , and is transported to a contact part of a pair of transport rollers  24  including a driving roller  24   a  and a driven roller  24   b.    
     The sheet guide  51  has a curved shape, and guides the sheet drawn by the sheet draw portion  22  to the pair of transport rollers  24 . 
     The photoconductor unit  30  is provided at the upper side (Z direction) of the sheet feed unit  20 , and includes a photoconductor drum  31  serving as an image holding body that is rotationally driven. The charging roller  32 , the exposure device LH, the development unit  40 , the transfer roller  62 , and a cleaning blade  34  are arranged along a rotation direction of the photoconductor drum  31 . A cleaning roller  33  is arranged to face and contact the charging roller  32 . The cleaning roller  33  cleans a surface of the charging roller  32 . 
     The development unit  40  includes a development housing  41  that houses a developer therein. The development housing  41  includes therein the development roller  42  arranged to face the photoconductor drum  31 , and a paddle wheel  43  arranged at the rear surface side, at the obliquely lower side of the development roller  42 . The paddle wheel  43  stirs the developer and transports the developer toward the development roller  42 . Further, a pair of augers  44  and  45  for stirring and transportation is arranged at the rear surface side of the paddle wheel  43 . A layer regulation roller  46  is arranged near the development roller  42 . The layer regulation roller  46  regulates a layer thickness of the developer. 
     A toner supply port  41   c  is formed at an upper surface at the front side (X direction) of the development housing  41 . A toner supply mechanism  47  is coupled to the toner supply port  41   c , and extends to the front. A supply auger  48  is rotatably supported in the toner supply mechanism  47 . A cartridge holder  49  is coupled to a front end of the toner supply mechanism  47 . A toner from a toner cartridge TC flows into the cartridge holder  49 . The supply auger  48  is driven in accordance with a consumption amount of the toner by the development unit  40 , and the developer is supplied from the toner cartridge TC to the development unit  40 . 
     A surface of the rotating photoconductor drum  31  is electrically charged by the charging roller  32 . Then, an electrostatic latent image is formed by latent-image forming light emitted from the exposure device LH. The electrostatic latent image formed on the photoconductor drum  31  is developed as a toner image by the development roller  42 . 
     The transfer and transport unit  60  includes a sheet guide  63  that guides the sheet sent from the pair of transport rollers  24  to a transfer contact part, the transfer roller  62 , a transport guide  65  that guides the sheet having the toner image transferred thereon to the fixing unit  70 . The transfer and transport unit  60  is located at the downstream side of the pair of transport rollers  24  in a sheet transport direction, and is supported so that the transfer and transport unit  60  may come into contact with and be separated from the body of the image forming apparatus  1  through the open and close panel  110 . 
     The power supply device  13  or other device controlled by the controller  11  applies a transfer voltage to the transfer roller  62 . The transfer roller  62  transfers the toner image on the photoconductor drum  31  onto the sheet sent from the pair of transport rollers  24  and guided by the sheet guide  63 . 
     The remaining toner on the surface of the photoconductor drum  31  is removed by the cleaning blade  34  and housed in the housing that supports the photoconductor drum  31 . The surface of the photoconductor drum  31  is electrically charged again by the charging roller  32 . The remaining substance which is not removed by the cleaning blade  34  and adheres to the charging roller  32  is caught by and accumulated on the surface of the cleaning roller  33  that rotates while contacting the charging roller  32 . 
     The fixing unit  70  includes a pair of fixing rollers  71  and  72 . A press region of the pair of fixing rollers  71  and  72  forms a fixing region. 
     The sheet having the toner image transferred thereon by the transfer unit is transported to the fixing unit  70  through the transport guide  65  in a state in which the toner image is not fixed. The toner image of the recording medium transported to the fixing unit  70  is fixed by an action of pressure and heat by the pair of fixing rollers  71  and  72 . The sheet having the fixed toner image formed thereon is guided by transport guides  74   a  and  74   b , and is output to the output tray portion T at the upper surface of the image forming apparatus  1  from an output roller pair  73 . 
     (2) Configuration and Operation of Sheet Transport Section 
       FIG. 2  is a schematic section illustrating an inner configuration and sheet transportation of the sheet transport section of the image forming apparatus  1  according to this exemplary embodiment.  FIG. 3  is a schematic partial section of the sheet transport section. The configuration and the operation of the sheet transport section of the image forming apparatus  1  are described below with reference to the drawings. 
     The sheet transport section includes the housing  100 , the open and close panel  110 , the sheet transport unit  50 , and the transfer and transport unit  60 . 
     (2.1) Housing 
     The housing  100  has an opening at the rear side (−X direction) and houses the photoconductor unit  30  and the development unit  40  in the opening. 
     The housing  100  includes both side plates  100   a . First bearing portions  101  serving as the rotation center of the open and close panel  110  are formed at lower ends at the opening side of the both side plates  100   a  to penetrate through the both side plates  100   a  in a plate thickness direction. The first bearing portions  101  rotatably support rotation shaft portions  111  (described later) of the open and close panel  110 . 
     Second bearing portions  102  are formed at the front side (X direction) of the first bearing portions  101 . The second bearing portions  102  rotatably support rotation shaft portions  53  (described later) of the sheet transport unit  50 . 
     The second bearing portions  102  have long hole shapes being long in the up-down direction (Z and −Z directions) of the housing  100 . The sheet transport unit  50  rotatably supported by the second bearing portions  102  may move in the up-down direction (Z and −Z directions) of the housing  100  within a range along the major axes of the long holes. 
     Recesses  103  serving as positioning portions are formed at the upper side (Z direction) of the first bearing portions  101  and the second bearing portions  102 . Part at the rear side (−X direction) of each of the recesses  103  is opened. The recess  103  includes fixed surfaces  103   a  and  103   b  located in the front-rear direction (X and −X directions) and a fixed surface  103   c  at the upper side (Z direction). The distance between the fixed surfaces  103   a  and  103   b  located in the front-rear direction (X and −X directions) is set to be substantially equal to a sectional shape (dimension) of each of engagement protrusions  54  (described later) of the sheet transport unit  50 . 
     That is, when the engagement protrusions  54  of the sheet transport unit  50  enter the recesses  103 , side surfaces  54   a  located in the front-rear direction (X and −X directions) of the engagement protrusions  54  come into contact with the fixed surfaces  103   a  and  103   b  located in the front-rear direction (X and −X directions) of the recesses  103 , and surfaces  54   b  at the upper side (Z direction) of the engagement protrusions  54  are positioned and regulated at the fixed surfaces  103   c.    
     The sheet guide  23  serving as the first transport unit that guides the sheet, which is drawn to the front side (−X direction) by the sheet draw portion  22 , to the pair of transport rollers  24  is fixed in the housing  100 . The driving roller  24   a  that forms one of the pair of transport rollers  24  is rotatably supported at the sheet guide  23 . 
     (2.2) Open and Close Panel 
     The open and close panel  110  includes the pair of left and right rotation shaft portions  111  at the lower end portion. The rotation shaft portions  111  are inserted and fitted to the first bearing portions  101  formed at the lower ends at the opening side of the both side plates  100   a  of the housing  100 , and hence the open and close panel  110  is rotatable. 
     A pair of left and right lower holder portions  112  is formed at the inner surface side of the open and close panel  110  facing the housing  100 . The lower holder portions  112  have guide grooves  112   a  with long hole shapes being long in the up-down direction (Z and −Z directions). Lower boss portions  66  (described later), which are formed at the transfer and transport unit  60 , are inserted and fitted to the lower holder portions  112 , and support the transfer and transport unit  60  movably in the up-down direction (Z and −Z directions). 
     Also, a pair of left and right upper holder portions  113  is formed at the upper side (Z direction) of the lower holder portions  112 . The upper holder portions  113  have guide grooves  113   a  with long hole shapes being long in the up-down direction (Z and −Z directions). Upper boss portions  67  (described later), which are formed at the transfer and transport unit  60 , are inserted and fitted to the upper holder portions  113 , and support the transfer and transport unit  60  movably in the up-down direction (Z and −Z directions). 
     A pair of left and right protrusions  116  serving as guide portions is formed at the inner surface side of the open and close panel  110  facing the housing  100 . The protrusions  116  include first tapered portions  116   a , second tapered portions  116   b  continued to the first tapered portions  116   a , and round-shape portions  116   c  continued to the second tapered portion  116   b . The protrusions  116  come into contact with protrusions  55  serving as guided portions (described later), which are provided at the open and close panel  110  side of the sheet transport unit  50  to face the protrusions  116 , in association with an open or close operation of the open and close panel  110 . Thus, the sheet transport unit  50  is guided to the recesses  103  serving as the positioning portions. 
     (2.3) Sheet Transport Unit 
     The sheet transport unit  50  includes the sheet guide  51  and the driven roller  24   b  forming the pair of transport rollers  24 . The sheet guide  51  has a sheet guide surface having plural guide ribs  52  formed thereon. The guide ribs  52  guide the sheet, which is stacked on the sheet stack plate  21  and drawn to the front side (−X direction) by the sheet draw portion  22 , to the contact part of the pair of transport rollers  24 . 
     The driven roller  24   b  is located at the downstream side (Z direction) of the sheet guide  51 , is urged to protrude toward the sheet guide surface from the guide ribs  52  by a spring member S 1 , and is supported rotatably in the sheet transport direction. 
     The pair of left and right rotation shaft portions  53  is formed at both the side surfaces of the sheet guide  51 . The rotation shaft portions  53  are inserted and fitted to the second bearing portions  102  formed at the both side plates  100   a  of the housing  100 . The sheet transport unit  50  is movable with respect to the housing  100 . 
     The rotation shaft portions  53  have columnar shapes. The outer diameter of each column is substantially equal to the width along the minor axis of each of the second bearing portions  102  formed in the long hole shapes being long in the up-down direction (Z and −Z directions) of the housing  100 . The rotation shaft portions  53  rotate in association with the open or close operation of the open and close panel  110  with less rattling, and are movable in the up-down direction (Z and −Z directions) of the housing  100  within the range along the major axes of the long holes. 
     The axes of the rotation shaft portions  53 , the rotation shaft portions  111 , the pair of transport rollers  24 , and the transfer roller  62  are parallel to each other. 
     The pair of left and right engagement protrusions  54  is formed at both the side surfaces of the sheet guide  51 . The engagement protrusions  54  are inserted and fitted to the recesses  103  serving as the positioning portions formed at the both side plates  100   a  of the housing  100 , the side surfaces  54   a  located in the front-rear direction (X and −X directions) of the engagement protrusions  54  come into contact with the fixed surfaces  103   a  and  103   b  located in the front-rear direction (X and −X directions) of the recesses  103 , and the surfaces  54   b  at the upper side (Z direction) of the engagement protrusions  54  are positioned and regulated at the fixed surfaces  103   c.    
     The pair of left and right protrusions  55  serving as the guided portions is formed at the other surface side of the sheet guide surface of the sheet guide  51 , to face the protrusions  116  formed at the inner surface side of the open and close panel  110 . When the open and close panel  110  is rotated, the protrusions  55  move while contacting the protrusions  116  of the open and close panel  110 , and the sheet transport unit  50  is guided to the recesses  103  serving as the positioning portions. 
     (2.4) Transfer and Transport Unit 
     The transfer and transport unit  60  includes a transfer and transport housing  61  and the transfer roller  62 . The transfer and transport housing  61  includes the sheet guide  63  that guides the sheet sent from the pair of transport rollers  24  to the transfer contact part, a transfer-roller holder portion  64  that holds the transfer roller  62 , and the transport guide  65  that guides the sheet having the toner image formed thereon to the fixing unit  70 , which are integrally formed. 
     The pair of left and right lower boss portions  66  is formed at both the side surfaces at the sheet guide  63  side of the transfer and transport housing  61 . The lower boss portions  66  are inserted and fitted to the guide grooves  112   a  with the long hole shapes being long in the up-down direction (Z and −Z directions) and provided at the lower holder portions  112  of the open and close panel  110 . 
     Also, the pair of left and right upper boss portions  67  is formed at both the side surfaces at the transport guide  65  side of the transfer and transport housing  61 . The upper boss portions  67  are inserted and fitted to the guide grooves  113   a  with the long hole shapes being long in the up-down direction (Z and −Z directions) and provided at the upper holder portions  113  of the open and close panel  110 . 
     Hence, the transfer and transport unit  60  is supported at the inner surface of the open and close panel  110  facing the housing  100 , movably in the up-down direction (Z and −Z directions). 
     Both end portions of the transfer roller  62  are urged by spring members (not illustrated), at the transfer-roller holder portion  64  to come into contact with the photoconductor drum  31  through bearing members  68 , and are rotatably supported at the transfer-roller holder portion  64  in the sheet transport direction. The bearing members  68  are positioned and engaged at hook portions  104  formed at the housing  100 . 
     (3) Operation of Sheet Transport Section 
     With the sheet transport section configured as described above, for example, when a user removes a sheet clogged at the sheet transport section, the sheet transport unit  50  and the transfer and transport unit  60  are rotated from the housing  100  in association with the open operation of the open and close panel  110 , and the contact state of the pair of transport rollers  24  is released. 
       FIGS. 4A and 4B  are schematic partial sections each explaining movement of the sheet transport unit  50  caused by the open operation of the open and close panel  110 .  FIGS. 5A to 5C  are schematic illustrations each explaining an example of a release structure of positioning engagement between the engagement protrusions  54  and the recesses  103 .  FIGS. 6A to 6C  are schematic partial illustrations each explaining movement of the sheet transport unit  50  caused by the close operation of the open and close panel  110 .  FIGS. 7A and 7B  are schematic partial illustrations each explaining movement of the transfer and transport unit  60  caused by the close operation of the open and close panel  110 . 
     When the open operation of the open and close panel  110  is started, the round-shape portions  116   c  of the open and close panel  110  pressing the protrusions  55  of the sheet transport unit  50  from the lower side move while contacting the protrusions  55 , and then move to a position at which the protrusions  55  come into contact with the second tapered portions  116   b  continued to the round-shape portions  116   c  (see  FIG. 4A ). 
     Then, when the contact between the protrusions  55  and the second tapered portions  116   b  is ended, and the open and close panel  110  is opened to a position at which the protrusions  55  come into contact with the first tapered portions  116   a , the engagement protrusions  54  of the sheet transport unit  50  move from the fixed surfaces  103   a  and  103   b  located in the front-rear direction (X and −X directions) of the recesses  103  to the open region, and the positioning engagement between the engagement protrusions  54  and the recesses  103  is released (see  FIG. 4B ). 
     The sheet transport unit  50  is moved by a reactive force of the contact received by the driven roller  24   b  forming the pair of transport rollers  24  in a direction in which the sheet guide  51  is separated, the contact between the pair of transport rollers  24  is released, and hence the clogged sheet may be easily removed. 
     It is to be noted that a force may be applied to the sheet transport unit  50  in a direction in which the contact between the pair of transport rollers  24  is released so that the contact between the pair of transport rollers  24  is reliably released when the open and close panel  110  moves to the open position. For example, a spring member S 2  may be used to constantly urge the sheet transport unit  50  to the lower side (−Z direction) of the housing  100 , so that the engagement protrusions  54  of the sheet transport unit  50  are reliably moved from the fixed surfaces  103   a  and  103   b  located in the front-rear direction (X and −X directions) of the recesses  103  to the open region and the positioning engagement between the engagement protrusions  54  and the recesses  103  is released (see  FIG. 5A ). 
     Alternatively, the fixed surfaces  103   a  of the recesses  103  and the side surfaces  54   a  of the engagement protrusions  54  may have tapered shapes, so that the positioning engagement between the engagement protrusions  54  and the recesses  103  is released by the reactive force of the contact received by the driven roller  24   b  forming the pair of transport rollers  24  (see  FIG. 5B ). 
     Still alternatively, a press-down protrusion U that comes into contact with the sheet transport unit  50  may be provided at the open and close panel  110 , so that the sheet transport unit  50  is moved to the lower side by the press-down protrusion U at the open operation of the open and close panel  110  (see  FIG. 5C ). 
     When the open and close panel  110  is returned from the open position to the closed position, the user rotates the open and close panel  110  toward the housing  100 . 
     The first tapered portions  116   a  of the protrusions  116  of the open and close panel  110  come into contact with the protrusions  55  of the sheet guide  51 , and the sheet transport unit  50  starts rotating around the rotation shaft portions  53  rotatably supported at the second bearing portions  102  of the housing  100 , toward the closed position of the housing  100  (see  FIG. 6A ). 
     Then, the sheet transport unit  50  is moved until the protrusions  55  of the sheet guide  51  are inserted and fitted to the recesses  103  while contacting the first tapered portions  116   a  of the open and close panel  110  by the movement of the open and close panel  110  to the closed position. 
     Then, the sheet transport unit  50  is positioned and held because the engagement protrusions  54  formed at both the side surfaces of the sheet guide  51  are inserted and fitted to the recesses  103  formed at the both side plates  100   a  of the housing  100  and serving as the positioning portions. 
     At this time, the driven roller  24   b  supported and urged to protrude from the guide ribs  52  of the sheet guide  51  to the sheet guide surface comes into contact with the driving roller  24   a  forming the pair of transport rollers  24 , and a reactive force caused by the contact acts on the open and close panel  110 . 
     The engagement protrusions  54  come into contact with the fixed surfaces  103   a  and  103   b  located in the front-rear direction (X and −X directions) and are regulated by the fixed surfaces  103   a  and  103   b  and move to come into contact with the fixed surfaces  103   c  located in the upper direction (Z direction) while contacting the second tapered portions  116   b  continued to the first tapered portions  116   a  (see  FIG. 6B ). 
     The rotation shaft portions  53  of the sheet transport unit  50  are moved in the up-down direction (Z and −Z directions) within the range along the major axis of the long holes of the second bearing portions  102  of the housing  100 . 
     The sheet transport unit  50  is supported while the protrusions  55  are pressed to the upper side (Z direction) by the round-shape portions  116   c  continued to the second tapered portions  116   b , and the sheet transport unit  50  is positioned and held at the recesses  103  of the housing  100  (see  FIG. 6C ). 
     At this time, the driven roller  24   b  supported and urged to protrude from the guide ribs  52  of the sheet guide  51  to the sheet guide surface comes into contact with the driving roller  24   a  forming the pair of transport rollers  24 . The reactive force of the contact is received by the surfaces ( 103   a ) of the recesses  103  opposing the direction in which the driven roller  24   b  receives the force. Accordingly, the reactive force acting on the open and close panel  110  is decreased and hence the open and close panel  110  is not deformed. 
     That is, the recesses  103  have the fixed surfaces  103   a  that are orthogonal to the direction in which the driven roller  24   b  receives the force, and the fixed surfaces  103   a  receive the reactive force acting on the pair of transport rollers  24 . 
     The reactive force of lifting the pair of transport rollers  24  to the upper side (Z direction) by the sheet transportation and the sheet transport unit  50  to the upper side (Z direction) by the frictional force of the sheet is received by the recesses  103 . The reactive force acting on the open and close panel  110  is decreased, and the open and close panel  110  is not deformed. 
     That is, the recesses  103  have the fixed surfaces  103   c  that are orthogonal to the direction in which the driven roller  24   b  receives the force by the sheet transportation, and the fixed surfaces  103   c  receive the force acting on the driven roller  24   b . Accordingly, the recesses  103  regulate the movement of the driven roller  24   b  in the Z direction. 
     Hence, the recesses  103  position the sheet transport unit  50  located at the closed position in the upper direction (Z direction) and the front-rear direction (X and −X directions), and the open and close panel  110  supports the gravity (−X direction) acting on the sheet transport unit  50 . 
     At the timing at which the sheet transport unit  50  is positioned at the recesses  103  serving as the first positioning portions of the housing  100 , in the transfer and transport unit  60  supported at the inner surface side of the open and close panel  110  movably in the up-down direction (Z and −Z directions), the bearing members  68  provided at both the end portions of the transfer roller  62  come into contact with tapered portions  104   a  of the hook portions  104  serving as positioning portions formed at the housing  100  (see  FIG. 7A ). 
     Then, by the movement of the open and close panel  110  to the closed position, the bearing members  68  of the transfer roller  62  slide and move while contacting the tapered portions  104   a , and are positioned and regulated at fixed surfaces  104   b  and  104   c  of the hook portions  104  (see  FIG. 7B ). 
     At this time, the transfer roller  62  urged to come into contact with the photoconductor drum  31  by the spring member (not shown) comes into contact with the photoconductor drum  31  and forms the transfer part. The reactive force of the contact acts on the open and close panel  110 . 
     The protrusions  55  are supported by the round-shape portions  116   c  continued to the second tapered portions  116   b  of the open and close panel  110 . The sheet transport unit  50  is held at the recesses  103  of the housing  100 . 
     As described above, when the open and close panel  110  is returned from the open position to the closed position, the sheet transport unit  50  and the transfer and transport unit  60  forming the sheet transport section are engaged at the housing  100 , and do not simultaneously form nip parts that cause the reactive forces to act on the open and close panel  110 . 
     That is, when the open and close panel  110  moves to the closed position, the sheet transport unit  50  engages with the recesses  103  of the housing  100  and is positioned, and then the transfer and transport unit  60  engages with the hook portions  104  of the housing  100  and is positioned. Hence, the reactive forces caused by the nip parts acting on the open and close panel  110  are dispersed, and the close operation of the open and close panel  110  may be easily performed. 
     Also, when the open and close panel  110  moves to the closed position, the reactive forces received from the sheet transport unit  50  and the transfer and transport unit  60  are dispersed, and breakage of the open and close panel  110  may be restricted. 
     Second Exemplary Embodiment 
     An image forming apparatus  1 A according to this exemplary embodiment has a basic configuration similar to the image forming apparatus  1 A according the first exemplary embodiment, except a structure of a recess  103 A serving as a positioning portion. Therefore, the same reference sings are applied to components common to the components of the image forming apparatus  1  of the first exemplary embodiment, and the detailed description is omitted. 
     (1) Configuration and Close Operation of Sheet Transport Section 
       FIG. 8  is a schematic partial section of the sheet transport section, and  FIGS. 9A and 9B  are schematic partial illustrations each explaining movement of a sheet transport unit  50 A by a close operation of an open and close panel  110 A. A configuration of the sheet transport section of the image forming apparatus  1 A and the close operation of the open and close panel  110 A are described below with reference to the drawings. 
     The sheet transport section includes the housing  100 , the open and close panel  110 A, the sheet transport unit  50 A, and the transfer and transport unit  60 . The recesses  103 A serving as positioning portions of the housing  100 , first protrusions  116 A serving as guide portions of the open and close panel  110 A, and the sheet guide  51  of the sheet transport unit  50 A are described below in detail. 
     (1.1) Housing 
     The housing  100  has an opening at the rear side (−X direction) and houses the photoconductor unit  30  and the development unit  40  in the opening. 
     The housing  100  includes both side plates  100   a . The first bearing portions  101  serving as the rotation center of the open and close panel  110 A are formed at lower ends at the opening side of the both side plates  100   a  to penetrate through the both side plates  100   a  in a plate thickness direction. The first bearing portions  101  rotatably support the rotation shaft portions  111  (described later) of the open and close panel  110 A. 
     The second bearing portions  102  are formed at the front side (X direction) of the first bearing portions  101 . The second bearing portions  102  rotatably support the rotation shaft portions  53  of the sheet transport unit  50 A. 
     The recesses  103 A serving as positioning portions are formed at the upper side (Z direction) of the first bearing portions  101  and the second bearing portions  102 . As shown in  FIG. 8 , each of the recesses  103 A includes a tapered portion  103 Aa, fixed surfaces  103 Ab and  103 Ac located in the front-rear direction (X and −X directions), and a fixed surface  103 Ad at the lower side (−Z direction). Part at the upper side (Z direction) of the recess  103 A is opened. 
     The engagement protrusions  54  of the sheet transport unit  50 A are guided to the tapered portions  103 Aa, and are positioned and regulated at the fixed surfaces  104   b  and  104   c.    
     To be more specific, the distance between the fixed surfaces  103 Ab and  103 Ac located in the front-rear direction (X and −X directions) is set to be substantially equal to the sectional shape (dimension) of each of the engagement protrusions  54  of the sheet transport unit  50 A. 
     When the engagement protrusions  54  of the sheet transport unit  50 A are fitted to the recesses  103 A while contacting the tapered portions  103 Aa, the side surfaces  54   a  located in the front-rear direction (X and −X directions) of the engagement protrusions  54  come into contact with the fixed surfaces  103 Ab and  103 Ac located in the front-rear direction (X and −X directions) of the recesses  103 A, and the surfaces  54   b  in the lower direction (−Z direction) of the engagement protrusions  54  are positioned and regulated at the fixed surfaces  103 Ad. 
     (1.2) Open and Close Panel 
     The open and close panel  110 A includes the pair of left and right rotation shaft portions  111  at the lower end portion. The rotation shaft portions  111  are inserted and fitted to the first bearing portions  101  formed at the lower ends at the opening side of the both side plates  100   a  of the housing  100 , and hence the open and close panel  110 A is rotatable. 
     A pair of left and right protrusions  116 A serving as guide portions is formed at the inner surface side of the open and close panel  110 A facing the housing  100 . The first protrusions  116 A contact first protrusions  55 A provided at the open and close panel  110 A side of the sheet transport unit  50 A to face the first protrusions  116 A and serving as guided portions, in association with the open or close operation of the open and close panel  110 A. The sheet transport unit  50 A is guided to the recesses  103 A serving as the positioning portions. 
     A pair of left and right second protrusions  117  is formed at the inner surface side of the open and close panel  110 A facing the housing  100 , at the outside of the first protrusions  116 A. The second protrusions  117  have pressing portions  117   a . The pressing portions  117   a  contact second protrusions  56  provided at the open and close panel  110 A side of the sheet transport unit  50 A to face the second protrusions  117 , in association with the open or close operation of the open and close panel  110 A. The sheet transport unit  50 A is pressed to the fixed surfaces  103 Ad of the recesses  103 A serving as the positioning portions and is positioned. 
     (1.3) Sheet Transport Unit 
     The sheet transport unit  50 A includes the sheet guide  51  and the driven roller  24   b  forming the pair of transport rollers  24 . The sheet guide  51  has the sheet guide surface having the plural guide ribs  52  formed thereon. The guide ribs  52  guide the sheet, which is stacked on the sheet stack plate  21  and drawn to the front side (−X direction) by the sheet draw portion  22 , to the contact part of the pair of transport rollers  24 . 
     The driven roller  24   b  is located at the downstream side (Z direction) of the sheet guide  51 , is urged to protrude toward the sheet guide surface from the guide ribs  52  by the spring member S 1 , and is supported rotatably in the sheet transport direction. 
     The pair of left and right rotation shaft portions  53  is formed at both the side surfaces of the sheet guide  51 . The rotation shaft portions  53  are inserted and fitted to the second bearing portions  102  formed at the both side plates  100   a  of the housing  100 . The sheet transport unit  50 A is movable with respect to the housing  100 . 
     The pair of left and right engagement protrusions  54  is formed at both the side surfaces of the sheet guide  51 . The engagement protrusions  54  are inserted and fitted to the recesses  103 A serving as the positioning portions formed at the both side plates  100   a  of the housing  100 , the side surfaces  54   a  located in the front-rear direction (X and −X directions) of the engagement protrusions  54  come into contact with the fixed surfaces  103 Ab and  103 Ac located in the front-rear direction (X and −X directions) of the recesses  103 A, and the surfaces  54   b  at the lower side (−Z direction) of the engagement protrusions  54  are supported at the fixed surfaces  103 Ad, and are positioned and regulated at the fixed surfaces  103 Ad. 
     The pair of left and right first protrusions  55 A serving as the guided portions is formed at the other surface side of the sheet guide surface of the sheet guide  51 , to face the first protrusions  116 A formed at the inner surface side of the open and close panel  110 A. The first protrusions  55 A move while contacting the first protrusions  116 A of the open and close panel  110 A by the rotation of the open and close panel  110 A, and are guided to the recesses  103 A serving as the positioning portions of the sheet transport unit  50 A (see  FIG. 9A ). 
     The pair of left and right second protrusions  56  is formed at the outside of the first protrusions  55 A to face the second protrusions  117  of the open and close panel  110 A. The second protrusions  56  come into contact with the pressing portions  117   a  of the second protrusions  117  provided at the open and close panel  110 A, in association with the close operation of the open and close panel  110 A (see  FIG. 9B ). The sheet transport unit  50 A is positioned and held in a state in which the sheet transport unit  50 A is pressed to the fixed surfaces  103 Ad of the recesses  103 A serving as the positioning portions. 
     (2) Operation 
     When the engagement protrusions  54  of the sheet transport unit  50 A move while contacting the tapered portions  103 Aa and are fitted to the recesses  103 A, the side surfaces  54   a  located in the front-rear direction (X and −X directions) of the engagement protrusions  54  come into contact with the fixed surfaces  103 Ab and  103 Ac located in the front-rear direction (X and −X directions) of the recesses  103 A. 
     Then, the surfaces  54   b  located in the lower direction (−Z direction) of the engagement protrusions  54  are supported at the fixed surfaces  103 Ad, and are positioned and held in a state in which the surfaces  54   b  are pressed by the pressing portions  117   a  of the second protrusions  117  of the open and close panel  110 A. 
     Hence, the driven roller  24   b  supported and urged to protrude from the guide ribs  52  of the sheet guide  51  to the sheet guide surface comes into contact with the driving roller  24   a  forming the pair of transport rollers  24 , and forms the contact. The reactive force of the contact is received by the recesses  103 A. Accordingly, the reactive force acting on the open and close panel  110 A is decreased and hence the open and close panel  110 A is not deformed. 
     That is, the recesses  103 A have the fixed surfaces  103 Ab that are orthogonal to the direction in which the driven roller  24   b  receives the force, and the fixed surfaces  103 Ab receive the reactive force acting on the pair of transport rollers  24 . 
     The reactive force of lifting the pair of transport rollers  24  by the sheet transportation and the sheet transport unit  50 A by the frictional force of the sheet is received by the rotation shaft portions  111  of the open and close panel  110 A through the pressing portions  117   a  of the second protrusions  117  provided at the open and close panel  110 A. Accordingly, the reactive force of pressing the open and close panel  110 A to the outside (−X direction) of the image forming apparatus  1 A is decreased, and the open and close panel  110 A is not deformed. 
     Further, since the recesses  103 A are opened in the upper direction (Z direction), when a sheet clogged in the pair of transport rollers  24  is pulled, the driven roller  24   b  is moved by the sheet, and the contact between the pair of transport rollers  24  is released. 
     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 modifications 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.