Abstract:
There is provided an image forming device that forms images on recording sheets. The image forming device includes a frame having an opening, a cover movable for opening and closing the opening, a drum unit, a belt unit and a pair of registration rollers. The drum unit is disposed in the frame and having plurality of photosensitive drums each defining an axis, the plurality of photosensitive drums being juxtaposed in line in a direction orthogonal to the axis. The belt unit is accommodated in the frame and having a plurality of rollers and an endless belt mounted over the plurality of rollers under tension, the endless belt having a first running part running in a sheet conveying direction and in direct confrontation with each of the photosensitive drums, the first running part extending in a first direction, the drum unit being movable in the first direction and accessible through the opening. The pair of registration rollers nips the recording sheets therebetween to correct skew in the recording sheets and to convey each recording sheet toward the belt unit, the pair of registration rollers being supported to the frame and disposed at a side opposite to the drum unit with respect to an imaginary plane which is an extension of the first running part, the pair of registration rollers defining a nip point therebetween where the recording sheet is nipped, the nip point being located at a position aligned with the belt unit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2008-017602 filed Jan. 29, 2008. The entire content of the priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an electrophotographic image forming device that forms images on recording sheets. 
       BACKGROUND 
       [0003]    In a direct-tandem color laser printer disclosed in Japanese patent publication no. 2006-98776, after a pair of registration rollers has corrected skew in a sheet conveyed from a feeding tray, the corrected sheet is then conveyed to a drum unit (image forming unit) including a plurality of photosensitive drums. 
         [0004]    In the above-mentioned invention, the drum unit is designed to be removable from the main casing, thereby enabling the photosensitive drums to be removed all at once from the main casing. Thus, this configuration facilitates maintenance of the drum unit. 
         [0005]    Generally, the registration rollers are designed to correct skew in recording sheets, such as sheets of paper, as described above. The registration rollers are, therefore, preferably disposed in as close proximity to the drum unit as possible. 
         [0006]    This is because, if the registration rollers are disposed in a position far away from the drum unit, a recording sheet may become skewed again before reaching the drum unit, even though the registration rollers had previously registered the sheet before conveying the sheet downstream. Another reason is that it is difficult to control the timing at which the registration rollers supply a recording sheet to the drum unit with a high degree of accuracy. 
         [0007]    On the other hand, if the registration rollers are disposed in proximity to the drum unit, the registration rollers and the drum unit may interfere with each other when the drum unit is being removed from the main casing simply by being pulled out in a horizontal direction. In such a case, it may not be easy to remove the drum unit from the main casing. 
         [0008]    In the invention disclosed in the above-identified publication, therefore, one of the registration rollers located closer to the drum unit is provided in the drum unit. According to this configuration, when the drum unit is being removed from the main casing, one of the registration rollers is removed together with the drum unit, thereby preventing interference between the registration rollers and the drum unit from occurring. 
         [0009]    As stated, a pair of registration rollers is provided for correcting skew in recording sheets, and, hence, one registration roller must be positioned relative to the other registration roller with a high degree of accuracy. However, as in the above-identified reference, when one of the registration rollers is configured to be removed together with the drum unit and the other registration roller is fixed to the main casing, it is difficult to achieve high positioning accuracy between the pair of registration rollers. 
         [0010]    Moreover, although another method may be employed to prevent interference between registration rollers and a drum unit by incorporating one of the registration rollers in a cover that opens/closes an opening for removing/mounting the drum unit, high positioning accuracy between the pair of registration rollers is still difficult to achieve, because one of the registration rollers is fixed to a movable unit while the other one is fixed to a main casing, as in the invention identified above. 
         [0011]    Further, high positioning accuracy between the registration rollers may be achieved even in the above-mentioned method if the movable, open/close cover is given high rigidity. However, this solution inevitably increases the weight and dimensions of the open/close cover, leading to a larger image forming device. 
         [0012]    In view of the forgoing, it is an object of the present invention to provide an image forming device that can be made compact and can realize easy removal of a drum unit while achieving high positioning accuracy between a pair of registration rollers. 
       SUMMARY 
       [0013]    The present invention is made in order to achieve the above and other objects. According to an aspect of the present invention, there is provided an electrophotographic image forming device that forms images on recording sheets. The image forming device includes a frame having an opening, a cover movable for opening and closing the opening, a drum unit, a belt unit and a pair of registration rollers. The drum unit is disposed in the frame and having a plurality of photosensitive drums each defining an axis, the plurality of photosensitive drums being juxtaposed in line in a direction orthogonal to the axis. The belt unit is accommodated in the frame and having a plurality of rollers and an endless belt mounted over the plurality of rollers under tension, the endless belt having a first running part running in a sheet conveying direction and in direct confrontation with each of the photosensitive drums, the first running part extending in a first direction, the drum unit being movable in the first direction and accessible through the opening. The pair of registration rollers nips the recording sheets therebetween to correct skew in the recording sheets and to convey each recording sheet toward the belt unit, the pair of registration rollers being supported to the frame and disposed at a side opposite to the drum unit with respect to an imaginary plane which is an extension of the first running part, the pair of registration rollers defining a nip point therebetween where the recording sheet is nipped, the nip point being located at a position aligned with the belt unit. 
         [0014]    According to another aspect of the invention, there is provided an electrophotographic image forming device that forms images on recording sheets, which includes a frame having an opening, a cover movable for opening and closing the opening, a drum unit, a belt unit and a pair of registration rollers. The drum unit is disposed in the frame and having a plurality of photosensitive drums each defining an axis, the plurality of photosensitive drums being juxtaposed in line in a direction orthogonal to the axis. The belt unit is accommodated in the frame and having a plurality of rollers and an endless belt mounted over the plurality of rollers under tension, the endless belt having a first running part running in a sheet conveying direction and in direct confrontation with each of the photosensitive drums, the first running part extending in a first direction, the drum unit being movable relative to the belt unit in the first direction and accessible through the opening. The pair of registration rollers nips the recording sheets therebetween to correct skew in the recording sheets and to convey each recording sheet toward the belt unit, the pair of registration rollers being supported to the frame and disposed at a side opposite to the drum unit with respect to an imaginary plane which is an extension of the first running part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0016]      FIG. 1  is a cross-sectional view showing main parts of the image forming device  1  according to the present embodiment; 
           [0017]      FIG. 2  is a perspective view from the left side of the main body (frame)  2  of the image forming device  1 ; 
           [0018]      FIG. 3  is a perspective view of a belt unit  30 ; 
           [0019]      FIG. 4  is a diagram illustrating the relationships of disposition between registration rollers  26 A and  26 B and the belt unit  30 ; 
           [0020]      FIG. 5  is a view showing detachment of the photosensitive unit  12 ; and 
           [0021]      FIG. 6  is a view showing detachment of the belt unit  30 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    An electrophotographic image forming device of the present invention is applied to a direct tandem color laser printer in the present embodiment. Hereinafter, the present embodiment will be described with accompanying drawings. 
         [0023]    A main body (frame)  2  shown in  FIG. 2  is covered with a casing  3 . On the upper surface of the casing  3  located is a discharge tray  4  onto which a plurality of sheets of paper or transparencies (hereinafter simply referred to as sheets) is discharged from the casing  3  after printing (image formation) has finished. 
         [0024]    As shown in  FIG. 2 , the main body  2  includes substantially plate-shaped side frames  2 A and  2 B, a top plate  2 C, and a bottom plate  2 D. The side frames  2 A and  2 B are disposed at both ends of the main body  2  in a horizontal (left-to-right) direction, and the top plate  2 C connects the two side frames  2 A and  2 B at the upper ends thereof, while the bottom plate  2 D connects the two side frames  2 A and  2 B at the lower ends thereof. Note that a pair of registration rollers  26 A and  26 B described later is omitted in  FIG. 2 . 
         [0025]    The main body  2  has an accommodation space  2 E that extends in a front-to-rear direction with the left-right sides thereof bounded by the side frames  2 A and  2 B. As shown in  FIGS. 1 and 5 , an opening  2 F provided at the front side of the accommodation space  2 E can be opened or closed by a door  3 A that is pivotably attached to the casing  3 . 
         [0026]    An image forming unit  10  including a drawer unit or the like, a feeder unit  20 , and a belt unit  30  are provided within the accommodation space  2 E of the main body  2 . After the image forming unit  10  has formed images on a sheet, an intermediate conveying roller  40  conveys the sheet along a discharging chute (not shown) that guides the sheet first upward and then forward so that the conveying direction changes substantially 180 degrees. Finally, a discharge roller  41  discharges the sheet onto the discharge tray. 
         [0027]    As shown in  FIG. 1 , the image forming unit  10  includes an exposing unit (scanner)  11 , a photosensitive unit  12 , a fixing unit  14 , and the like. 
         [0028]    In the image forming unit  10  according to the present embodiment, four developer cartridges  13 K,  13 Y,  13 N and  13 C are juxtaposed in line along the sheet conveying direction in order from the upstream side thereof. The four developer cartridges  13 K,  13 Y,  13 M and  13 C respectively correspond to four colors of developer (toner): black, yellow, magenta, and cyan. Each of the four colors of developer is sequentially superimposed onto a sheet while the sheet is being conveyed on the belt unit  30 . 
         [0029]    The exposing unit  11  is disposed in the upper portion of the casing  3 . The exposing unit  11  serves to form electrostatic latent images on the surface of a photosensitive unit  13 D (described later), and specifically includes a laser source, a polygon mirror, an fθ lens, and reflection mirrors. 
         [0030]    The laser beam emitted from the laser source according to image data is deflected and scanned by the polygon mirror, passes through the fθ lens, reverses directions along a different optical path when reflected by a reflection mirror, and then follows a downward path when reflected by another reflection mirror. The laser beam is finally irradiated onto the surface of the photosensitive drum  13 D on which electrostatic latent images are formed. 
         [0031]    The photosensitive unit  12  has four developer cartridges  13 K,  13 Y,  13 M and  13 C (hereinafter collectively referred to as developer cartridges  13 ). The developer cartridges  13  are accommodated in a drawer casing  12 A capable of moving in the front-to-rear direction with respect to the main body  2 . The developer cartridges  13  and the drawer casing  12 A that accommodates the developer cartridges  13  integrally constitute a drawer unit (drum unit). 
         [0032]    Hence, in this embodiment, four developer cartridges (the developer cartridges  13 ) can be integrally removed from/mounted on the main body  2 . A guide roller  12 B is provided with the drawer casing  12 A (photosensitive unit  12 ) at the advancing side in the mounting direction of the drawer casing  12 A (i.e., rear side) with respect to the main body  2 . A guide rail  2 G is in sliding contact with the guide roller  12 B to guide the photosensitive unit  12  into the correct mounting position thereof. 
         [0033]    Note that black developer is accommodated in the developer cartridge  13 K, yellow developer in the developer cartridge  13 Y, magenta developer in the developer cartridge  13 M, and cyan developer in the developer cartridge  13 C. 
         [0034]    Also note that all of the four developer cartridges have the same configuration except in that each accommodates developers of a different color. Details of the configuration of the developer cartridges are as described below. 
         [0035]    A developer accommodating unit  13 A includes a developer accommodating chamber  13 B that accommodates developer, a supplying roller  13 E that supplies developer onto the photosensitive drum  13 D, and a developing roller  13 F and the like. The developer accommodated in the accommodating chamber  13 B is supplied to the developing roller  13 F side in accordance with the rotation of the supplying roller  13 E, then carried on the surface of the developer roller  13 F while the thickness of the carried developer is adjusted to a constant prescribed thickness by a thickness-regulating blade  13 G, and finally supplied onto the surface of the photosensitive drum  13 D exposed by the exposing unit  11 . 
         [0036]    The photosensitive drum  13 D serves to carry images to be transferred onto sheets. The photosensitive drum  13 D is provided in each of the four developing cartridges. The four photosensitive drums  13 D are juxtaposed in line in a direction orthogonal to the axial direction thereof, that is, in the sheet conveying direction. 
         [0037]    A charger  13 H serves to charge the surface of the photosensitive drum  13 D. A transferring roller  13 J is disposed in opposition to the photosensitive drum  13 D via the conveying belt  33 . The transferring roller  13 J applies to sheets a voltage having a polarity opposite the charge generated on the surface of the photosensitive drum  13 D when the sheets pass in the vicinity of the photosensitive drum  13 D, and transfers developer carried on the surface of the photosensitive drum  13 D onto the printing surfaces of the sheets. 
         [0038]    In the present embodiment, the transferring roller  13 J is rotatably provided in the belt unit  30 , and arranged so as to be in contact with the back side of the conveying belt  33 . The transferring roller  13 J rotates along with the movement of the conveying belt  33 . 
         [0039]    A fixing unit  14  is disposed downstream of the photosensitive drum  13 D in the sheet conveying direction. The fixing unit  14  heats and melts the developer transferred onto the sheets for fixation, and is detachably mounted on the main body  2 . 
         [0040]    Specifically, the fixing unit  14  includes a heating roller  14 A, a pressure roller  14 B, and the like. The heating roller  14 A is disposed on the printing surface side of the sheet, and applies a conveying force to the sheet while heating the developer thereon. The pressure roller  14 B is disposed in confrontation with the heating roller  14 A via the sheet, and presses the sheet against the heating roller  14 A side. 
         [0041]    A belt unit  30  works in conjunction with the operation of the photosensitive unit  12  to convey sheets. As shown in  FIG. 1 , the belt unit  30  is disposed in a position below the photosensitive unit  12 , and detachably mounted in the main body  2 . 
         [0042]    The belt unit  30  includes a drive roller  31 , a follow roller (tension roller)  32 , a conveying belt that is mounted in a taut state on the drive roller  31  and the follow roller  32 , and a belt unit frame  34  (see  FIG. 3 ) that supports the drive roller  31  and the follow roller  32 . The drive roller  31  is configured to rotate in conjunction with the rotation of the photosensitive drum  13 D. The follow roller  32  is rotatably disposed in a position distanced from the drive roller  31 . The conveying belt  33  has a first conveying portion  33 A (upper portion) that confronts each of the photosensitive drums  13 D. 
         [0043]    The first conveying portion  33 A is a surface on which each sheet is placed and conveyed. The photosensitive unit  12  can be moved in a direction parallel to the plane of the first conveying portion  33 A, i.e., a direction that passes through the rotational centers of the drive roller  31  and the follow roller  32  (in this embodiment, the front-to-rear direction). That is, the photosensitive unit  12  is detachably mounted in the main body  2  with respect to the extending direction of the first conveying portion  33 A (the front-to-rear direction) in this embodiment. 
         [0044]    When the photosensitive unit  12  is removed, as shown in  FIG. 6 , the belt unit  30  can then be taken out from the main body  2  by lifting the front end portion of the belt unit  30  upward and thus releasing from a tension lever  36  (to be described later). 
         [0045]    The rotational shaft of the drive roller  31  is rotatably assembled on the belt unit frame  34  at a fixed position with respect to the same via a bearing (not shown). 
         [0046]    The rotational shaft of the follow roller  32 , on the other hand, is provided with bearings (not shown) at the axial ends thereof and is assembled on the belt unit frame  34  in such a manner that the rotational shaft can be inserted into elongated holes (not shown) formed in the belt unit frame  34 . With this construction, the rotational shaft can be displaced in a direction toward or away from the drive roller  31 . 
         [0047]    When the belt unit  30  is mounted in a correct mounting position with respect to the main body  2 , as shown in  FIG. 1 , a biasing member such as a coil spring  35  applies a biasing force to the follow roller  32  via the tension lever  36 , pushing the follow roller  32  in a direction away from the drive roller  31 . 
         [0048]    As shown in  FIG. 1 , the belt unit  30  (belt unit frame  34 ) has protrusions  34 A that protrude to the side frames  2 A and  2 B constituting a part of the main body  2 . On the side frames  2 A and  2 B, engaging portions  2 H are provided for engaging with the protrusions  34 A at the follow roller  32  side thereof, when the belt unit  30  is placed in the correct mounting position with respect to the main body  2 . 
         [0049]    Accordingly, when the belt unit  30  is placed in the correct mounting position with respect to the main body  2 , the engagement with the protrusions  34 A and the engaging portions  2 H can prevent the belt unit  30  from moving toward the follow roller  32  side, and the biasing force applied from the tension lever  36  can transmit a prescribed tension from the follow roller  32  to the conveying belt  33 . 
         [0050]    Note that the correct mounting position refers to a position at which the belt unit  30  can operate normally. If the belt unit  30  is not mounted in the correct mounting position, the sheets cannot be conveyed normally, thereby leading to a degradation in the quality of images formed on the sheets, or occurrence of paper jams and the like while the sheet is being conveyed. 
         [0051]    A feeder unit  20  serves to convey sheets stacked in a sheet feeding tray  21  (described later). More particularly, as shown in  FIG. 1 , the feeder unit  20  includes a sheet feeding tray  21 , a pick-up roller  22 , a sheet feeding roller  23  and the like. The sheet feeding tray  21  is disposed in the lowest portion of the main body  2 , and a plurality of sheets is accommodated therein in a stacked state. The pick-up roller  22  picks up a sheet from among the sheets stacked in the sheet feeding tray  21 . The sheet feeding roller  23  feeds (conveys) the sheet picked up by the pick-up roller  22  to the image forming unit  10  side. 
         [0052]    A separating pad  24  is disposed in confrontation with the sheet feeding roller  23  with sheets being conveyed therebetween. The separating pad  24  serves to prevent a plurality of sheets from being conveyed at a time by applying a predetermined resistance to a conveyed sheet, enabling only one sheet that touches the sheet feeding roller  23  to be conveyed. 
         [0053]    Note that the separating pad  24  is assembled on the sheet feeding tray  21 , and a biasing member, such as a coil spring  24 A, applies a biasing force to the separating pad  24 , pressing the separating pad  24  against the sheet feeding roller  23 . On the other hand, the sheet feeding roller  23  is rotatably assembled on the main body  2 . The pick-up roller  22  is assembled on a tip portion of a pivoting arm (not shown) that is pivotably assembled on the main body  2 . 
         [0054]    As shown in  FIG. 4 , a pair of conveying rollers  25 A and  25 B is provided downstream of the sheet feeding roller  23  in the conveying direction for conveying sheets to the pair of registration rollers  26 A and  26 B. 
         [0055]    Note that the conveying roller  25 A is rotatably assembled on the main body  2 , while the conveying roller  25 B is rotatably assembled on the sheet feeding tray  21 . A biasing member, such as a coil spring  25 C, applies a biasing force to the conveying roller  25 B, pressing the conveying roller  25 B to the conveying roller  25 A (see  FIG. 1 ). 
         [0056]    The registration rollers  26 A and  26 B convey sheets to the belt unit  30  and also serve to correct skew in the conveyed sheets. The registration rollers  26 A and  26 B are rotatably supported in the main body  2  at both axial ends thereof, and are disposed on the opposite side of an imaginary plane S 1  that includes the first conveying portion  33 A of the conveying belt  33  from the photosensitive unit  12  (i.e., below the imaginary plane S 1  in this embodiment). 
         [0057]    The registration rollers  26 A and  26 B pinch each sheet at a nip point P, which is located at a position aligned with the belt unit  30  in the extending direction of the belt unit  30  (the front-to-rear direction in this embodiment). That is, the nip pint P is positioned in a space formed between the imaginary plane S 1  and an imaginary plane S 2  that includes a second conveying portion  33 B (lower portion of the conveying belt  33 ) located in opposition to the first conveying portion  33 R via the follow roller  32 . 
         [0058]    Guides  25 D and  25 E serve to guide sheets conveyed out of the pair of conveying rollers  25 A and  25 B along a U-shaped path that runs upward and rearward toward the pair of registration rollers  26 A and  26 B. Hence, the guides  25 D and  25 E change the sheet conveying direction substantially 180 degrees. 
         [0059]    Note that, because the registration rollers  26 A and  26 B are both disposed in a position opposing the photosensitive unit  12  with respect to the imaginary plane S 1 , as shown in  FIG. 4 , the tangential direction of the nip point P, i.e., a conveying direction D of the sheets conveyed from the registration rollers  26 A and  26 B inevitably intersects with the imaginary plane S 1 . 
         [0060]    Hence, in this embodiment, a first guide  27 A and a second guide  27 B are provided for guiding the sheets conveyed from the registration rollers  26 A and  26 B toward the conveying belt  33 . 
         [0061]    A sheet conveying path L is formed from the sheet feeding tray  21  to the belt unit  30  and is substantially U-shaped. The first guide  27 A is disposed in a position opposing to the center of curvature of the sheet conveying path L and serves to change the sheet conveying direction toward the center of curvature. The first guide  27 A is assembled on the door  3 A, and therefore, as shown in  FIGS. 5 and 6 , is displaced mechanically in association with the (opening/closing) movement of the door  3 A. 
         [0062]    As shown in  FIG. 4 , the second guide  27 B is disposed in confrontation with the first guide  27 A via the sheet conveying path L and serves in cooperation with the first guide  27 A to guide the sheets conveyed from the registration rollers  26 A and  26 B toward the conveying belt  33 . The second guide  27 B is provided in the belt unit  30 , as shown in  FIG. 3 . 
         [0063]    Note that the circumferential velocity of the registration rollers  2 GA and  26 B is set to be greater than the moving velocity of the conveying belt  33 . Accordingly, when a leading edge of a conveyed sheet reaches the conveying belt  33 , a conveying force generated by the registration rollers  26 A and  26 B urges the sheet to curl so that the curved part protrudes toward the opposite side of the sheet conveying path L from the center of curvature. 
         [0064]    Hence, in this embodiment, as shown in  FIG. 4 , at least a portion of the first guide  27 A is arranged to be located on the same side of the imaginary plane S 1  as the photosensitive unit  12 , as well as to turn the sheet conveying direction toward the conveying belt  33  from the photosensitive unit  12  side of the imaginary plane S 1 . 
         [0065]    That is, as indicated by the dotted line A in  FIG. 4 , once a sheet conveyed from the registration rollers  26 A and  26 B reaches the photosensitive unit  12  side beyond the imaginary plane S 1 , the first guide  27 A changes the conveying direction of the sheet toward the imaginary plane  51 , and subsequently guides the sheet to the conveying belt  33 . 
         [0066]    Because the circumferential speed of the pair of registration rollers is larger than the moving speed of the conveying belt, a sheet goes slack between the registration rollers  26 A and  26 B and the conveying belt  33 , thereby enabling the sheet to be in close contact with the conveying belt  33 . 
         [0067]    In the present invention, the registration rollers  26 A and  26 B are supported in the main body  2  and disposed at the opposite side of the photosensitive unit  12  with respect to the imaginary plane S 1 . This configuration can contribute to downsizing of the image forming device  1 , while achieving high positioning accuracy between the pair of registration rollers  26 A and  26 B. 
         [0068]    Also, since the pair of registration rollers is disposed on the opposite side of the imaginary plane S 1  from the photosensitive unit  12 , interference between the registration rollers  26 A and  26 B and the photosensitive unit  12  can be prevented when the photosensitive unit  12  is to be removed from the main body  2 , as shown in  FIG. 5 . 
         [0069]    Moreover, since the nip point P of the pair of registration rollers  26 A and  26 B is located in a position aligned with the belt unit  30  in the extending direction of the belt unit  30  (the front-to-rear direction), as shown in  FIG. 4 , the registration rollers  26 A and  26 B can be disposed in the vicinity of the photosensitive unit  12 , Accordingly, the registration rollers  26 A and  26 B can reliably correct skew generated in sheets to be supplied to the photosensitive unit  12 , and can control the timing at which the sheets are supplied to the photosensitive unit  12  with great accuracy. 
         [0070]    Hence, in this embodiment, the photosensitive unit  12  can be easily detached from the main body  2 , while the overall size of the image forming device  1  can be made compact and the positioning accuracy between the pair of registration rollers  26 A and  26 B can be highly maintained. 
         [0071]    Further, in this embodiment, the first guide  27 A and the second guide  27 B are provided for guiding the sheets sent from the pair of registration rollers  26 A and  26 B to the conveying belt  33 , thereby ensuring that the sheets be conveyed to the photosensitive unit  12 . 
         [0072]    The first guide  27 A is arranged so as to be displaced along with the opening/closing operations of the door  3 A, thereby avoiding interference with the photosensitive unit  12  when the photosensitive unit  12  is removed from the main body  2 . 
         [0073]    The first guide  27 A is also configured to separate from the second guide  27 B when the door  3 A is opened, thereby facilitating removal of jammed papers even when a paper jam occurs around the first guide  27 A. 
         [0074]    Note that the first guide  27 A serves to change the sheet conveying direction in order to guide the sheet toward the photosensitive unit  12 , and therefore, does not require the same positioning accuracy required for the registration rollers  26 A and  26 B. Hence, changing positions of the first guide  27 A affects the image formation by the image forming device  1  very little. 
         [0075]    The second guide  27 B is designed to remain stationary even when the door  3 A is opened, since the second guide  27 B is disposed on the belt unit  30 . As shown in  FIG. 4 , the second guide  27 B is disposed on the opposite side of the imaginary plane S 1  from the photosensitive unit  12 , i.e., below the imaginary line S 1 . Accordingly, this configuration prohibits the second guide  27 B from interfering with the photosensitive unit  12  when the photosensitive unit  12  is being detached from the main body  2 . 
         [0076]    Further, in the present embodiment, the pair of registration rollers  26 A and  26 B sends out sheets in a direction that intersects with the imaginary plane S 1 , and the first guide  27 A changes the conveying direction of the sheets conveyed from the registration rollers  26 A and  26 B toward the conveying belt  33  on the photosensitive unit  12  side of the imaginary plane S 1 . Because of this configuration, the conveying path of the sheets conveyed from the registration rollers  26 A and  26 B (the dotted line A in  FIG. 4 ) first crosses the imaginary plane S 1 , and then approaches the first conveying portion  33 A of the conveying belt  33  at an acute angle. Hence, the air existing between each sheet and the conveying belt  33  can be effectively expelled, thereby enabling the sheet to be placed reliably on the conveying belt  33   
         [0077]    As a variation of the present embodiment, it is not necessary for the photosensitive unit  12  to be capable of moving (detaching) in the front-to-rear direction (i.e., substantially in the horizontal direction). 
         [0078]    The belt unit  30  according to the present embodiment is provided for conveying sheets, but the belt unit  30  may instead be used for the intermediate transfer of developer. 
         [0079]    As an alternative to the exposing device, a plurality of LED lights may be controlled and used to expose the photosensitive drums  13 D, instead of using a scanner that employs laser beams. 
         [0080]    Although the present invention has been described with respect to specific embodiments, it will be appreciated by one skilled in the art that a variety of changes may be made without departing from the spirits of the invention.