Abstract:
The present invention relates to an image forming apparatus including an image carrier unit having an image carrier for carrying an image and a transfer material carrier unit having a transfer material carrier for carrying a transfer material, the transfer material carrier unit being capable of assuming a first state when the image on the image carrier is transferred onto a transfer material carried by the transfer material carrier and a second state that the transfer material carrier unit escapes more than the first state. The image carrier unit is detachably attached to an apparatus body through a space formed in the apparatus body after the transfer material carrier unit enters in the second state.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an image forming apparatus using an electrophotographic method and, more particularly, to an image forming apparatus such as a printer, facsimile machine, or photocopier. 
     2. Description of Related Art 
     As shown in FIG. 16, conventional color image forming apparatuses  100  using an electrophotographic method frequently use an inline method in which multicolor image carriers  102  are arranged in a row. In FIG. 16, the respective image carriers  102  are formed with electrophotostatic latent images by an exposing means  103 , and carry toner images visualized by multicolor toners by means of developing means. A transfer material sent out of a feeding section  104  by a feeding roller  105  receives by transfer the respective color toner images from the image carriers  102  by an electrostatically attracting transfer belt  106 , and is delivered to a delivery means  108  provided outside the machine body and stacked there after images are fixed to the transfer material with the application of heat and pressure from a fixing means  107 . 
     Color image forming apparatuses of the inline type used currently, in major part, use LEDs as exposing means as shown in FIG. 17, and such exposing means  103  are structured to be open and closed in a united body with a top lid. The respective exposing means  103  are placed at predetermined positions upon closing the top lid and are immobilized by being pushed by utilizing a compression spring. 
     However, the image forming apparatus as shown in FIG. 17 is required to move the exposing means together with the top lid when a process cartridge  101  is maintained or replaced or paper jamming recovery is made. Thus, as opening and closing operations of the top lid are repeated, positions of the exposing means correlative to the image carriers are more or less shifted, thereby deviating the exposure positions. This deviation of the exposure positions renders formed images shifted or inclined, and when color images are formed, image defects may occur due to a color shift or like. 
     To avoid the above problems, a possible structure is that the process cartridge can be removed from an upper portion of the apparatus without moving the exposing means, but this structure is required to dispose the exposing means and the process cartridge in a non-overlapping manner in a horizontal direction in FIG. 17, so that the structure may raise a problem that apparatus may be made larger. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an image forming apparatus capable of maintaining and replacing the image carrier units and improving the workability of paper-jamming recovery. 
     Another object of the invention may become apparent when the following detailed description is read. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an entire view showing an image forming apparatus according to a first embodiment; 
     FIG. 2 is an entire view of an image forming apparatus, showing an open state of a transfer means; 
     FIG. 3 is a schematic perspective view showing an image forming apparatus; 
     FIG. 4 is an illustration describing a joint movement plate in a state that the transfer means is closed; 
     FIG. 5 is an illustration describing the joint movement plate in a state that the transfer means is open; 
     FIG. 6 is a plain view describing a drive joint in a state that the transfer means is closed; 
     FIG. 7 is a plain view describing the drive joint in a state that the transfer means is open; 
     FIG. 8 is a view describing a coupling of the drive joint; 
     FIG. 9 is a side view of a process cartridge; 
     FIG. 10 is an illustration showing the state that the process cartridge is secured; 
     FIG. 11 is an illustration the state that the secured process cartridge is released; 
     FIG. 12 is an illustration showing an optical path shielding shutter in a state that the transfer means is closed; 
     FIG. 13 is an illustration showing an optical path shielding shutter in a state that the transfer means is open; 
     FIG. 14 is an illustration describing a structure of an image forming apparatus according to a second embodiment; 
     FIG. 15 is an illustration describing a structure of an image forming apparatus according to a third embodiment; 
     FIG. 16 is an illustration describing a structure of a conventional image forming apparatus; and 
     FIG. 17 is an illustration describing opening and closing operation of the apparatus in the conventional apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, embodiments according to the invention are described below. 
     First Embodiment 
     In this embodiment, as an image forming apparatus, a full color laser beam printer A is described as an example. 
     A full color laser beam printer A as shown in FIG. 1 has four image carriers  1   a  to  1   d  arranged in a vertical direction. Each of the image carriers  1  is rotatively driven in a counterclockwise direction in FIG. 1 by a drive means, not shown. Provided around the image carrier  1  in the order of the rotational direction are charging means  2   a  to  2   d  for uniformly charging surfaces of the image carriers  1 , scanner units  3   a  to  3   d  serving as exposing means for forming electrostatic latent images on the image carrier  1  by irradiating the image carrier with a laser beam based on image information, developing means  4   a  to  4   d  for developing toner images by adhering negatively charged toner to the electrostatic latent images, a conveyance apparatus  5  for conveying a transfer material to transfer the toner images on the image carrier  1  to a sheet S as a transfer material, and cleaning means  6   a  to  6   d  for removing post-transfer remaining toner remaining on the surface of the image carrier after transfer. The image carriers  1 , the charging means  2 , the developing means  4 , and the cleaning means  6  are made in a united body and into a cartridge, thereby forming a process cartridge  7  as an image carrier unit. 
     The image carrier  1  is structured of an aluminum cylinder having, e.g., a diameter of 30 mm and an outer peripheral surface coated with an organic photo-conductive layer (OPC photosensitive material). The image carrier  1  is supported as freely rotatable by a support member at each end of the carrier, and the drive force from a drive motor is transmitted to one end, thereby rotatively driving the carrier in the counterclockwise direction. 
     As such a charging means  2 , used is a contact charging type. The charging means  2  is a conductive roller formed in a roller shape, and the roller is made in contact with the surface of the image carrier  1  and is biased to a charging bias voltage (e.g., negative, in this embodiment), thereby charging the surface of the image carrier  12  uniformly. 
     The scanner unit  3  is disposed approximately at the rear of the image carrier  1 . Image lights corresponding to image signals emitted out of laser diodes, not shown, irradiate polygonal mirrors  9   a  to  9   d  as scanning means, which are rotated at a high rate by a scanner motor. The image light reflected at the polygonal mirror forms electrostatic latent images by selectively exposing to the light the surface of image carriers  1  which are charged by focusing lenses  10   a  to  10   d . Each of the developing means  4   a  to  4   d  is constituted of a developer containing each color among yellow, magenta, cyan, and black. 
     The conveyance apparatus  5  as a transfer material carrier unit is structured to have, as a united body, an electrostatically attracting conveyance belt (hereinafter referred to as conveyance belt  11 ) serving as a transfer material carrier for conveying the sheet S upon attracting the sheet so that the belt is in contact with all the image carriers  1   a  to  1   d  as opposing to the carriers. The conveyance belt  11  is made of a film shaped member having a peripheral length of about 700 mm and thickness of about 150 μm and has a volume eigen-resistance of 10 11  to 10 14  Ω·m. This conveyance belt  11  is supported in a vertical direction by four axes of a drive roller  13 , driven rollers  14   a ,  14   b , a tension roller  15 , attracts the sheet S electrostatically on the outer peripheral surface on a left side, and moves circularly in rendering the sheet S in contact with the image carriers  1 . 
     Transfer rollers  12   a  to  12   d  as transfer means are disposed at positions respectively corresponding to the image carriers  1   a  to  1   d  inside the conveyance belt  11 . Charges having positive polarity out of those transfer rollers  12  are applied to the sheet S via the conveyance belt  11 , and toner images having negative polarity on the image carrier  1  are transferred on the sheet S in contact with the image carrier  1 . 
     A feeding section  16  for feeding the sheet S is disposed at a lower portion of the apparatus body. Plural sheets are contained in feeding cassettes  17  of the feeding section  16 , and the feeding section  16  feeds separately the sheets S, sheet by sheet, in the feeding cassettes  17  where feeding rollers  18 , in a half moon shape, drive rotatively during image formation. The front end of the fed sheet S stops temporarily when contacting a register roller  19 , thereby correcting oblique feeding while forming a loop, and the sheet S is fed to the conveyance belt  11  in synchrony with the image writing start position of the image carrier  1 . 
     A fixing section  20  is for fixing toner images of multiple colors transferred on the sheet S and is constituted of a rotatable heating roller  21   a  and a pressing roller  21   b  for application of heat and pressure to the sheet S in pressed contact with the heating roller  21 . That is, the sheet S with the transferred toner image on the image carrier  1  is conveyed by the heating roller  21   a  and the pressing roller  21   b  when passing the fixing section  20 , and the toner image is fixed to a surface of the sheet S by application of heat and pressure. 
     [Image Forming Operation] 
     To form images, process cartridges  7   a  to  7   d  are sequentially driven in meeting the recording timings, and the image carriers  1   a  to  1   d  rotatively drive in the counterclockwise direction according to the drive. Then, the scanner units  3  corresponding to the process cartridges  7  are sequentially driven. With this drive, the charging means  2  provides uniform charges to the surface of the image carrier  1 , and the scanner unit  3  makes exposure around the image carrier  1  according to the image signals, thereby forming an electrostatic latent image on the peripheral surface of the image carrier  1 , and thereby forming the toner images by transferring toner in the developing means  4  to a lower potential portion (dark portion) of the electrostatic latent image. 
     The register roller pair  19  is rotatively driven in synchrony with the image carrier  1 , and the sheet is so conveyed that the front end of the toner image on the peripheral surface of the image carrier  1  on the most unstream side coincides to the recording starting position of the sheet S. The sheet S is in pressurized contact with the conveyance belt  11  by being pushed by the electrostatic attracting roller  22 . Electric charges are induced at the sheet S as a dielectric body and a dielectric layer of the conveyance belt  11  by application of voltage between the conveyance belt  11  and the electrostatic attracting roller  22  thereby attracting the sheet electrostatically on the outer peripheral surface of the conveyance belt  11 . Thus, the sheet S is attracted stably by the conveyance belt  11  and conveyed to the transfer portion on the most downstream side. While conveyed in such a manner the respective color toner images on the image carriers  1  are sequentially transferred to the sheet S by an electric field formed between the respective image carrier  1  and the transfer roller  12 . 
     The sheet S, with four color (yellow, magenta, cyan, black) transferred toner images, is separated according to the curvature from the conveyance belt  11  by the curvature of the drive roller  13 , and is conveyed to the fixing section  20 . The sheet S, after the toner images are fixed at the fixing section  20 , is delivered out of the apparatus body in a state that the image surface faces down from the delivery portion  24  by the delivery roller pair  23 . 
     Next, a joint movement mechanism operational in association with swinging, opening and closing of the conveyance apparatus  5 , a feature of the invention, will be described. As shown in FIG. 2, the conveyance apparatus  5  is structured to be rotatable about a rotary shaft as a center, and upon disengagement of a lock lever, not shown, the apparatus can swing and be open and closed toward a front side of the apparatus body. That is, the conveyance apparatus  5  can take two states: a state that the toner image on the image carrier is transferred to the transfer material (state that the image carrier and the conveyance belt are in contact with each other), and a state that the image carrier is kept further away than the above state (state that the conveyance belt is separated from the image carrier). Thus, while the conveyance apparatus  5  is set in the closed state, the sheet S can be conveyed as facing up in the approximately vertical direction. After the conveyance apparatus  5  is swung, or moved pivotally, the process cartridges  7   a  to  7   d  are detachably attached to the front aside of the apparatus body in a direction substantially perpendicular to the rotary shaft of the image carrier in utilizing a space formed within the apparatus body, so that the respective process cartridges  7  can be replaced and the respective color toners can be filled. Furthermore, when paper jamming occurs, the jammed paper on the conveyance belt  11  can be removed easily. 
     Thus, the respective process cartridges and the conveyance apparatus are structured to be detachably attachable to the front aside of the apparatus body in about the same direction. The apparatus body can be prevented from lowering the rigidity of the apparatus body because the apparatus body can be structured without, in two side plates placed at the front, rear, right and left sides as forming the apparatus body, any large cutouts such that each of the process cartridge and the conveyance apparatus can pass through. 
     Because the process cartridge and the conveyance apparatus are detachable from the apparatus body in a direction substantially perpendicular to the respective rotary shafts, the side plates directly or indirectly supporting the rotary shafts can be prevented from lowering the rigidity of the side plates, so that the invented mechanism can prevent rotational deviations from occurring in the process cartridge and the conveyance apparatus. 
     FIG.  4  and FIG. 5 are detailed views showing a joint state of a joint movement plate  29  and a conveyance apparatus  5 . FIG. 4 shows a closed state of the conveyance apparatus  5 ; FIG. 5 shows an open state of the conveyance apparatus  5 . In FIG. 4, the joint movement plate  29  is urged by an E ring to secured shafts  31   a  to  31   c  formed at a left side plate  25  and mounted slidably up and down in a range of long holes  32   a  to  32   c  formed in the joint movement plate  29 . The secured shaft  33  formed at the joint movement plate  29  is connected with a cam sliding groove  40  formed at the lateral sliding plate  34 . 
     Lateral sliding grooves  37   a ,  37   b  formed at the lateral sliding plate  34  are connected to secured shafts  38   a ,  38   b  formed at the left side plate  25 , and the lateral sliding plate  34  is formed slidably in a lateral direction in a width of the lateral sliding grooves  37   a ,  37   b . A vertical sliding groove  39  formed at the lateral sliding plate  34  is connected to a secured shaft  42  formed at a frame  41  of the conveyance apparatus  5 . 
     Accordingly, when the conveyance apparatus  5  is made open by rotating the conveyance apparatus  5  around a rotary shaft (swinging shaft)  43  as a center from a state in FIG. 4 to a state in FIG. 5, the secured shaft  42  formed at the frame  41  pushes the vertical sliding groove  39  of the lateral sliding plate  34 , thereby moving the lateral sliding plate  34  toward the outside of the apparatus from the state as shown in FIG. 4 to the state as shown in FIG.  5 . The joint movement plate  29 , according to this motion, moves to a lower portion as shown in FIG. 5 where the secured shaft  33  is pushed by a cam slider  40  of the lateral sliding plate  34 . 
     The joint movement plate  29  is herein structured to connect an engagement and disengagement mechanism for coupling and for transmitting a rotational drive force to the respective image carriers  1  of the process cartridges  7  in connecting to the rotary shaft of each image carrier  1 , an opening and closing mechanism of a protection cover for covering the respective image carriers  1  to prevent users from touching the surface of the photosensitive body, a securing mechanism for securing with pressure and releasing the respective process cartridges  7  at predetermined positions of the apparatus body, and an opening and closing mechanism of a light path shielding shutter for shielding the light path from the exposing means to the image carrier, and each of which jointly moves according to opening and closing of the conveyance apparatus  5 . Hereinafter, each mechanism is describe. 
     [Coupling for connecting image carrier drive] 
     As shown in FIG. 4, coupling engagement and disengagement levers  46   a  to  46   d , serving as connection disengaging means for drive transmission to the image carrier, are formed on the rotary shafts of the image carriers  1 . Coupling engagement brackets  44   a  to  44   d  and coupling disengagement brackets  46   a  to  46   d  are provided at the joint movement plate  29 . As described above, where the conveyance apparatus  5  is in the closed state, the joint movement plate  29  is located upwardly, and the coupling engagement brackets  44   a  to  44   d  render the coupling engagement and disengagement levers  46   a  to  46   d  are moved pivotally upward. 
     FIG. 6 is a view showing the coupling mechanism in the engagement state when viewed from the top. As shown in FIG. 6, a coupling  47  on the drive side is secured to a coupling shaft  48 , and the coupling shaft  48  is supported slidably in the up and down directions in FIG. 6 by bearings  50   a , 50   b  of a cylinder  49 . A gear  51  is secured to the other end of the coupling shaft  48  for transmission of a rotary drive force from a drive source, not shown. 
     The coupling engagement and disengagement lever  46  rotates over the coupling shaft  48  at the bearing  52 , fits movably in a thrust direction, and connects via a lever portion  53  with the coupling engagement bracket  44  of the joint movement plate  29 . The coupling shaft  48  is urged toward the side of the image carrier  1  (upper direction in FIG. 6) by a compression spring  54 . A projection  55  is formed on an outer peripheral surface of the bearing of the coupling engagement and disengagement lever  46 , and a projection  49   a  is formed on the cylinder  49 , so that both of the projections are engaged with each other where not hitting to each other. 
     A driven coupling  56  is secured to an end face of the rotary shaft of the image carrier  1  of the process cartridge  7  and engages with a drive coupling  57  to transmit the rotary drive force. The driven coupling  56  and the drive coupling  57  are couplings in a triangle spiral shape as shown in FIG. 8, and the compression spring  54  pushes the couplings where the drive coupling  47  rotates in a predetermined direction, so that the couplings always engages with each other. 
     Where the conveyance apparatus  5  is made to be shifted from the closed state in FIG. 4 to the open state as shown in FIG. 5, the joint movement plate  29  moves downward via the lateral sliding plate  34  as described above. The coupling disengagement bracket  45  at that time pushes the lever portion  53  of the coupling engagement disengagement lever  46  as shown in FIG. 7 to rotate about the coupling shaft  48  as a center. The projection  55  of the coupling engagement disengagement lever  46  then rides over the projection  49   a  of the cylinder  49  in opposing the force of the compression spring  54  and moves downward in FIG.  7 . According to this movement, the coupling shaft  48 , and the drive coupling  47  come to move, thereby disengaging the mesh of the couplings. 
     Where the conveyance apparatus  5  is made to be shifted from the open state in FIG. 5 to the closed state in FIG. 4, the reverse operations are made to engage the drive coupling  47  and the driven coupling  56  with each other. In regard with coupling means as an engagement disengagement means for transmitting a drive force to a development sleeve serving as a developer carrier for conveying a developing section in carrying developers in the developing means  4 , and coupling means as an engagement and disengagement means for transmitting a drive force to conveying means for conveying waste toner collected by the cleaning means  6  (cleaning blade), the similar structure becomes operational. 
     [Image Carrier Protection Cover Opening and Closing Mechanism] 
     As shown in FIG. 4, protection covers  57   a  to  57   d  serving as moving members are formed at the image carriers  1 . This protection cover  57  avoids the image carrier  1  to be exposed while the conveyance apparatus  5  is disengaged and prevents dusts from attaching and image defects from occurring due to the surface receiving damages. 
     As shown in FIG. 9, opening and closing levers  58   a  to  58   d  serving as opening and closing drive means of the protection cover  57  are supported by rotary shafts  59   a  to  59   d , respectively and constitute link mechanisms with opening and closing guide pins  60 . Each of the opening and closing levers  58   a  to  58   d  has one end connected to a protection cover  57  and a pin portion  58   a  as the other end. That is, by moving up and down the pin portion  58   a , the protection cover  57  can be made to open and close with respect to the image carrier  1  as shown with solid lines and dotted lines, respectively. The pin portions  58   a  are inserted in the opening and closing lever grooves  61   a  to  61   d , respectively, of the joint movement plate  29  as shown in FIG.  4 . 
     As shown in FIG. 4, where the conveyance apparatus  5  is in a closed state, the joint movement plate  29  is located upward as described above. At that time, the pin portion  58   a  is lifted up by the opening and closing lever groove  61 , and the protection cover  57  is located downward to expose the image carrier  1 . 
     Then, as shown in FIG. 5, where the conveyance apparatus  5  is opened, and where the joint movement plate  29  is moved downward, the opening and closing lever groove  61  moves the pin portion  58   s  down, and by the link mechanism, the protection cover  57  moves to a position covering the image carrier surface. Where the conveyance apparatus  5  is closed, the opening and closing lever groove  61  pushes up the pin portion  58   a , thereby causing the protection cover  57  to escape from the image carrier surface. With the apparatus thus structured, when the conveyance apparatus  5  is open to treat paper jamming, the image carrier surface can be always protected, and the apparatus can prevent dusts from attaching and users from mistakenly touching and damaging the surface. 
     [Process Cartridge Securing Mechanism] 
     FIG. 10 is a detailed view showing the process cartridge in a state that the process cartridge is secured to the apparatus body; FIG. 11 is a detailed view showing the process cartridge in a state that the secured process cartridge is disengaged from the apparatus body. In this embodiment, cartridge securing levers  64   a  to  64   d  are provided as securing means for engaging and disengaging the image carrier to and from the apparatus body, and by closing the conveyance apparatus  5 , the bearings  62   a  to  62   d  are pushed against the cutouts  63   a  to  63   d , thereby securing the image carriers  1 . 
     The process cartridge  7  is structured, as described above, as to be detachably attached to the apparatus body. When the process cartridge  7  is attached, guide ribs arranged on both sides of the process cartridge  7  are inserted into cartridge guides  28  provided on right and left side plates and guided through the guides. The bearing  62  of the image carrier  1  then hits, as shown in FIG. 10, the cutout  63  for positioning formed in the right side plate  26  and the left side plate  25 . Meanwhile, the cartridge securing lever  64  is arranged at the apparatus body and supported via a rotary shaft  65  to the right and left side plates  25 ,  26 . A securing assisting plate  66  is attached to the rotary shaft  65 , thereby linking between the end of the cartridge securing lever  64  and a pulling spring  67 . 
     As shown in FIG.  4  and FIG. 10, in the state that the conveyance apparatus  5  is closed, the joint movement plate  29  is located upward through the lateral sliding plate  34 , and a securing assisting plate pushing portion  68  formed at the joint movement plate  29  pushes up a securing pin  66   a  of the securing assisting plate  66 . Then, according to rotation of the securing assisting plate  66 , the cartridge securing lever  64  pivotally moves by operation of the pulling spring  67 , and the bearing  62  of the image carrier  1  is secured by being pushed with a predetermined spring pressure against the cutout  63  of the apparatus body. 
     As shown in FIG.  5  and FIG. 11, in the state that the conveyance apparatus  5  is opened, the joint movement plate  29  moves downward through the lateral sliding plate  34 , and the securing assisting plate pushing portion  68  formed at the joint movement plate  29  pushes down the securing pin  66   a  of the securing assisting plate  66 . Then, the cartridge securing lever  64  rotates in the counterclockwise direction around the rotary shaft  65  as a center, and the bearing  62  of the image carrier  1  is disengaged as shown in FIG.  5  and FIG. 11, thereby entering into a state that the process cartridge  7  can be pulled out. 
     [Light Path Shielding Shutter Opening and Closing Mechanism] 
     In this embodiment, a light path shielding shutter  71  is provided for shielding the light path from the scanner unit  3  as exposing means to the image carrier  1 . The light path shielding shutter  71  is a plate material disposed along a vertical stay  70  of the apparatus body as shown in FIG.  12 . The shutter is slidably structured in taking the shielding position and non-shielding position by passing a securing shaft  70   b  formed at the vertical stay  70  to a long hole  71   b  of the light path shielding shutter  71 . In the vertical stay  70  and the light path shielding shutter  71 , light path holes  70   a ,  71   a  are formed between the scanner units  3  and the image carriers  1 . 
     A sliding plate  73  is formed below the conveyance apparatus  5 , and a cam  74  changes the direction of force and is in contact with a projection  71   c  of the light path shielding shutter  71 . Accordingly, as shown in FIG. 12, where the conveyance apparatus  5  is closed, the light path shielding shutter  71  is pushed up, and in this state, the light path holes  70   a ,  71   a  becomes coaxial to open the light path. 
     As shown in FIG. 13, when the conveyance apparatus  5  is opened, the light path shielding shutter  71  moves down by self-weight or a link, thereby shielding the light path to the image carrier  1  from the scanner unit  3  by a shift between the light path hole  70   a  of the vertical stay  70  and the light path hole  71  a of the light path shielding shutter  71 . With this structure, even where the conveyance apparatus  5  is opened and closed to attach or detach the process cartridge  7 , the apparatus can prevent external light from reaching the scanner unit  3 . 
     Second Embodiment 
     A second embodiment of the image forming apparatus according to the invention is described in reference to the drawings. FIG. 14 is an entire view of the image forming apparatus according to this embodiment, and in regard to portions corresponding to the portions in the first embodiment, a duplicated description is omitted in providing the same reference numbers. 
     In the above embodiment, in use of the conveyance apparatus  5 , a toner image is directly transferred to a sheet conveyed from the image carrier  1 , and the sheet S is delivered onto a top of the apparatus. However, in this embodiment, this apparatus includes an intermediate transfer unit  75  equipped with an intermediate transfer belt  76  as an intermediate transfer body, which is detachably attached to the apparatus body. With such an apparatus thus structured, the respective engagement disengagement means and the like can be moved jointly with swinging, opening, and closing of the intermediate transfer unit  75  in the same way as in the first embodiment. 
     The intermediate transfer unit  75  includes, as a united body, a drive roller  77 , a driven roller  78   a ,  78   b , and a tension roller  79  for tensioning the intermediate transfer belt  76 . The intermediate transfer belt  76  is rotatively driven via a drive roller  77  from the drive source, not shown. The unit includes, as a united body, primary transfer rollers  80   a  to  80   d  formed on an inner peripheral side of the intermediate transfer belt  76 , and the intermediate transfer belt  76  is pushed to the respective image carriers  1   a  to  1   d , thereby transferring the toner images onto the intermediate transfer belt  76  in an overlapping manner. 
     A secondary transfer roller  81  (secondary transfer section) is arranged in opposing to the driven roller  78   a  located below the intermediate transfer unit  75  and secondarily transfers the toner images at a time on the intermediate transfer belt  76  to the sheet fed from the feeding section  16 . Then, the sheet is conveyed to the fixing section  20  disposed on the rear side of the apparatus and delivered to and stacked at a delivery tray  82  after images are fixed in application of heats and pressure. 
     This invention is applicable, in substantially the same way as, to the image forming apparatus using such an intermediate transfer body. That is, after the intermediate transfer body unit is set in a state that the intermediate transfer body unit escapes (in X direction) from the respective image carriers as shifted from the state of the intermediate transfer body during the transfer process (the state that the intermediate transfer belt is in contact with the respective image carriers), the respective process cartridges can be detachably attached in Y direction utilizing a space formed in the apparatus body. 
     Where the intermediate transfer body unit is set in the escaping state, and even where a sheet may wrap over the intermediate transfer body unit at the secondary transfer section, such a wrapped sheet can be removed easily. 
     Third Embodiment 
     Referring to the drawings, a third embodiment of the image forming apparatus according to the invention is described. FIG. 15 is an entire view of the image forming apparatus according to the embodiment, and in regard with portions corresponding to the portions in the first embodiment, duplicated description is omitted in providing the same reference numbers. 
     In the above embodiment, the conveyance apparatus  5  is attached to a holder arranged at the apparatus body by connecting a connecting portion  84 . The holder  83  is formed rotatably with a rotary shaft  43  with respect to the apparatus body. The holder  83  has a secured shaft  42  and is structured to jointly move the lateral sliding plate  34  and the joint movement plates  29 ,  30  in the same way as in the above embodiments. 
     The holder  83  has a hole  83   a , and on the other hand, a snap fitter  84   a  is formed at the connecting portion  84  of the conveyance apparatus  5 . The snap fitter  84   a  projects in the hole  83   a  from the elasticity of the fitter when the connecting portion  84  is inserted in the holder  83 , thereby engaging the conveyance apparatus  5  so as not to detach therefrom easily. When the connecting portion  84  is detached from the holder  83 , the snap fitter  84   a  is pushed through the hole  83   a  to remove the conveyance apparatus  5  upon releasing the engagement. The connecting portion  84  can be engaged to the holder  83  using nuts or other engaging means, not shown. 
     With the apparatus thus structured, the conveyance apparatus  5  can detachably attached very easily, and the conveyance belt  11  can be easily maintained and replaced. 
     Moreover, with respect to the intermediate transfer body unit as shown in the second embodiment, the detachably attaching mechanism of the conveyance apparatus  5  is applicable in substantially the same way as in the second embodiment. 
     Although in the above three embodiments the conveyance apparatus  5  or the intermediate transfer body unit  75  takes the state during the two states: the transfer process and the escaping state, this invention is not limited to this. For example, between jobs for image formation, the intermediate transfer body unit may be in a waiting mode as an intermediate state between the above two states (or a state having a shorter isolation distance than that of the escaping state). 
     As the above escaping state, for example, the respective process cartridge can be maintained, and replaced and the jammed paper can be removed in utilizing a space formed in the apparatus body created after the conveyance apparatus  5  or the intermediate transfer body unit  75  is pulled out of the apparatus body in a parallel direction toward the right side (see, FIG. 1, FIG.  14 ). That is, during maintenance and replacement work, the conveyance apparatus  5  or the intermediate transfer body unit  75  can be completely taken out of the apparatus body. 
     Although in the above embodiments the unit is to be swung after the door (a part of the external wall of the apparatus front side) on the front side of the apparatus body is opened, this invention is not limited to this. This invention is applicable where the door (external wall) is structured in a united body with the unit.