Abstract:
An image forming apparatus includes housing, an intermediate transferring body, a transferring member, a cover member, and a transferring member moving mechanism. The intermediate transferring body is removable from the housing along the rotation axis of the intermediate transferring body. A transferring member transfers the image from the intermediate transferring body to a transferring material. A cover member supports the transferring member and opens and closes in the direction that is perpendicular to the rotation axis of the intermediate transferring body. A transferring member moving mechanism moves the transferring member between a first position that the transferring member contacts with the intermediate transferring body and a second position that the transferring member removes from the intermediate transferring body.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This document claims priority to, and contains subject matter related to, Japanese Patent Applications No. 2004-271479, filed on Sep. 17, 2004, which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image forming apparatus such as a copier, a laser beam printer, an LED printer and a facsimile using a belt unit. The present invention relates to an image forming apparatus including an intermediate belt unit that can be attached to and detached from a main body of the image forming apparatus.  
         [0004]     2. Discussion of the Background  
         [0005]     The use of various transfer components, including a transfer bet, to transfer an image in an image forming apparatus using an electrophotographic method, is well-known. Because such components are expendable supplies, transfer belts and related components are preferably accessible and/or removable from an image forming apparatus. Also, as known to all users of image forming devices, paper jams are possible, thus requiring improved paper flow designs and easy access to paper flow paths.  
         [0006]     Japanese Patent Laid-Open No. 11-73035 describes an image forming apparatus that includes an intermediate transfer belt unit, which is removable from the apparatus along a rotational axis of the intermediate transfer belt. However, additional transfer elements are not easily accessed via an access plate and are not easily removable for component repair/replacement and paper jam clearing.  
         [0007]     Japanese Patent Laid-Open No. 11-352741 describes an image forming apparatus that includes a first side plate, a second side plate, an image support body, a developing device and an intermediate transfer component. The image support body, the developing device and the intermediate transfer component are disposed between the first side plate and the second side plate and removable respectively. The image support body and the developing device are removable in a direction perpendicular to the side plates. The intermediate transfer component is removable in a direction perpendicular from a rotational axis of the intermediate transfer belt. However, the intermediate transfer component is not removable along a rotational axis of the intermediate transfer component. Also, additional transfer elements are not easily accessed via an access plate and are not easily removable for component repair/replacement and paper jam clearing.  
         [0008]     Japanese Patent Laid-Open No. 2000-231321 describes an image forming apparatus that includes a transfer roller within an access component. However, this reference does not include an intermediate transfer device of any sort. Thus, this device also does not include a transfer device movement mechanism configured to move the transfer roller in and out of contact with an intermediate transfer device. Also, additional transfer elements are not easily accessed via an access plate and are not easily removable for component repair/replacement and paper jam clearing. Furthermore, this apparatus is not configured for color operations.  
         [0009]     Thus, as discovered by the present inventors, what is desired is a construction that allows for easier access and removal of intermediate and other transfer devices.  
       SUMMARY OF THE INVENTION  
       [0010]     It is a general object of the present invention to provide a belt unit in which one or more of the above-mentioned problems are eliminated.  
         [0011]     A first object of the present invention is to provide an improved image forming apparatus including an intermediate transfer body unit which can be easily attached and detached from the image forming apparatus without abutting a surface of an image support body.  
         [0012]     A second object of the present invention is to provide an improved image forming apparatus which can easily perform jam processing as necessary.  
         [0013]     In order to achieve the above-mentioned objects, there is provided, according to one aspect of the present invention, an image forming apparatus including a housing, an image support body, a developing member, an intermediate transferring body, a transferring member, a cover member, and a transferring member moving mechanism. The intermediate transferring body is removable from inside of the housing to outside along the rotation axis of the intermediate transferring body. A transferring member transfers the image from the intermediate transferring body to a transferring material. A cover member supports the transferring member and opens and closes in the direction that is perpendicular to the rotation axis of the intermediate transferring body. A transferring member moving mechanism moves the transferring member between a first position where the transferring member contacts with the intermediate transferring body, and a second position where the transferring member is not in contact with the intermediate transferring body.  
         [0014]     A third object of the present invention is to provide a novel method of attaching a transferring body to a housing of an image forming apparatus in a detachable manner.  
         [0015]     In order to achieve the above-mentioned third object, there is provided, according to one aspect of the present invention, a method and apparatus for attaching a transferring body to a housing of an image forming apparatus in a detachable manner that includes steps and devices for inserting, positioning, closing, locking. Here, the transferring body is inserted into the apparatus along the rotation axis of the transferring body through an opening of the housing. The transferring body is then positioned in the housing. The opening of the housing is covered by a plate. The transferring body is locked with a first locking mechanism.  
         [0016]     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0018]      FIG. 1  shows an exemplary structure of an image forming apparatus according to an embodiment of the present invention.  
         [0019]      FIG. 2  is a perspective view showing a frame constitution of a main body of the image forming apparatus.  
         [0020]      FIG. 3  is a perspective view showing an intermediate transfer body unit when the intermediate transfer body unit is supported by guide-rails.  
         [0021]      FIGS. 4A and 4B  are schematic views showing a locking mechanism that regulates removing of the intermediate transfer body unit.  
         [0022]      FIGS. 4C and 4D  are schematic views showing a detecting mechanism that detects locking of the intermediate transfer body unit.  
         [0023]      FIGS. 5A and 5B  are schematic views showing a locking member  53   a  that regulates removing of the intermediate transfer body unit.  
         [0024]      FIG. 6  is schematic view showing opening of a second transferring cover at the time of jam processing.  
         [0025]      FIG. 7  is schematic view showing a state of a second transferring roller at the time of non-image processing.  
         [0026]      FIG. 8  is schematic view showing the state of the second transferring roller at the time of image processing.  
         [0027]      FIG. 9  is schematic view -showing an attaching and detaching mechanism of the second transferring roller to and from the intermediate transfer body unit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     The best mode for carrying out the invention is explained below with reference to the figures. The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.  
         [0029]     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
         [0030]     A present embodiment is constituted as a full color printer using an intermediate transferring method.  
         [0031]      FIG. 1  shows an intermediate transfer belt  11  supported by support rollers  12 ,  13 ,  14  is disposed approximately centrally of a main body of an image forming apparatus in the crosswise direction. Four image-forming units are aligned along lower running side of the intermediate transfer belt  11 .  
         [0032]     Image forming elements, such as a charging device  4  configured to charge the photoconductor  1 , a developing device  5  configured to develop a latent image on the photoconductor  1  by each color toner into a toner image, a cleaning device  2  for removing toner particles remaining on the photoconductor  1 , are placed around the photoconductor  1  respectively. This image-forming unit preferably can serve as a process cartridge.  
         [0033]     Though the components of the image forming units a, b, c and d is similar, the color of toner contained in each developing device  5  is magenta, cyan, yellow, black respectively, is different from each other. An exposing device  6  is disposed in the lower part from the image-forming unit. The exposing device  6  forms a latent image by irradiating a laser beam corresponding to each color image information in a surface of the photoconductor  1 . Also, it is possible to adopt an exposing device including LED array and image forming mechanisms.  
         [0034]     The intermediate transfer belt  11  includes a resin film or rubber substratum having 50-600 μm in thickness. The intermediate transfer belt  11  has a resistance value that enables a toner to transfer from photoconductor  1 . As shown in  FIG. 1 , the intermediate transfer belt  11  is rotated in counterclockwise by a drive roller  12  coupled with drive mechanisms (not shown). A transfer roller  17 , which is a first transferring mechanism, is placed at a backside surface of the intermediate transfer belt  11 , which is contact with and opposed to the photoconductor  1 . These intermediate transfer belts  11 , support rollers  12 ,  13 ,  14  and the first transfer roller  17  are possible to be attached and detached to and from the main body of image forming apparatus together as a intermediate transfer device.  
         [0035]     A cleaning device  15 , having cleaning blade  16  configured to clean the toner and paper powders remaining on the surface of intermediate transfer belt  11 , is disposed at a position opposed to the support roller  13  in the outside of the belt loop. The cleaning device  15  with the intermediate transferring device  10  is removal from the main body of the image forming apparatus as an intermediate transferring unit  20 . A mechanism and a method of attachment and detachment are described below. In addition, of course, it is possible the cleaning unit  15  can be attached and detached from the intermediate transferring device  10  and the main body of the image forming apparatus.  
         [0036]     In the drawings, a second transferring unit  30  is disposed in the right side of the intermediate transfer belt  11 . A transfer roller  34 , as a re-transfer member (second transferring member), configured to transfer the toner from the intermediate transfer belt  11  to a recording medium is disposed at the vicinity of the drive roller  12  supporting the  10  intermediate transfer belt  11  in the second transferring unit  30 . When the image forming is not performed, the transfer roller  34  becomes to slightly separate from the intermediate transfer belt  11  as a normal position. On the contrary, when the image forming is performed, the transfer roller  34  is pressed to contact with the intermediate transfer belt  11  by pressing member. A mechanism of attachment and detachment of the transfer roller to the intermediate  15 , transfer belt is described below.  
         [0037]     Paper feeding cassettes  26 - 1 ,  26 - 2  including papers P as recording mediums are disposed in a paper supplying device at a lower part of the main body of the image forming apparatus.  
         [0038]     A paper in the highest position of the paper feeding cassette is fed by a feeding device  20  including paper rollers  27 , and guided by plural guide member  29  and  25 , and transported to a resisting roller pair  28 .  
         [0039]     A fusing device  36  including a source of heat such as a heater is disposed at the upper part above the second transferring unit  30 . An outputting guide  37  and an outputting roller  38  are placed behind the fusing device  36 .  
         [0040]     The second transferring cover  40  configured to support the second transferring unit  30  and to constitute a part of the main body has a structure that is possible to rotate and open around a shaft  24 . When a paper jam occurs, the second transferring cover  40  is opened to remove the paper from a path of paper transportation easily.  
         [0041]     An outputting stack portion  39  is formed on the top surface of the main body of the image forming apparatus.  
         [0042]     A toner cartridge containing portion TS configured to contain four toner cartridges TC including supplying toner is disposed in the lower part of the outputting stack portion  39  and the upper part of the intermediate transfer belt  11 . Colors of the toner of the toner cartridges TC are four colors of magenta, cyan, yellow and black, and the toner is supplied to a developing device  5  corresponding to color of the toner by a powder pump device (not shown).  
         [0043]     A process for forming an image with the image forming apparatus constructed as above is explained below.  
         [0044]     A signal for writing is sent by a host machine such as a computer. The exposing device  6  is driven based on a received image signal. A light from a laser light source (not shown) of the exposing device is scanned by a polygon mirror rotationally driven by a motor, and is irradiated to a photoconductor drum  1  uniformly charged with electricity with the charging device  4 , through mirrors, to form a latent image corresponding to a writing information on the photoconductor drum  1 .  
         [0045]     The latent image formed on the photoconductor drum  1  is developed with the toner of the developing device  5 , then, the toner image is formed and held on the surface of the photoconductor drum  1 . The toner image is transferred from the photoconductor drum  1  to the surface of the intermediate transfer belt  11 , which moves to synchronize with the photoconductor drum  1 , by the first transferring roller  17 .  
         [0046]     After toner image transferring, the toner remaining on the surface of the photoconductor drum  1  is cleaned by the cleaning device  2 . After that, the photoconductor drum  1  is neutralized by a charging neutralization device  3 , and entered a standby state for next image producing cycle.  
         [0047]     The intermediate transfer belt  11  moves to a direction shown in  FIG. 1  as an arrow, carrying the toner image transferred from the photoconductor drum  1  in the image forming unit a. Also, a latent image corresponding to another color is formed in a photoconductor drum  1   b  in an image forming unit b, and is developed with a toner of corresponding color to be a toner image. This toner image is overlaid on the toner image that is formed on the intermediate transfer belt  11  previously. Finally, a full color image is obtained by overlying the four-colored toner images formed by the image forming units a, b, c, d respectively.  
         [0048]     When the toner image on the intermediate transfer belt  11  moves to a predetermined place, paper feeding is started. Paper rollers  27  rotate in the direction of the arrow. The paper in the highest position of the paper feeding cassette  26 - 1  or  26 - 2  is drawn by the feeding device including paper rollers  27 , and the paper is transported to the resisting roller pair  28 . The paper is fed from the resisting roller pair  28  so that a four-color overlaid toner image on the intermediate transfer belt  11  is transferred to a side of the paper P sent between the intermediate transfer belt  11  and the secondary transcription roller  34 . An operation of the resisting roller pair  28  is controlled and/or timed so that the transfer media (e.g., paper) is presented to a nip position at roller  34  at the appropriate time.  
         [0049]     In this embodiment, polarity of an electrostatic latent image formed in the surface of the photoconductor drum  1  is positive, and polarity of the toner formed on the photoconductor  1  is negative. The toner held on the photoconductor  1  is transferred to the intermediate transfer belt  11  by giving an electric charge larger than that of the latent image of the photoconductor  1  to the first transferring roller  17 . In addition, the toner held on the intermediate transfer belt  11  is transferred to the paper P by giving an electric plus charge to the second transferring roller  34 .  
         [0050]     The paper P holding the toner image on the surface of itself as above is transported to the fixing device  36  and fixed. Then, the paper is transported through the outputting guide  37 , and outputted to the outputting stack portion  39  by the outputting roller  38 .  
         [0051]     When the outputting stack portion  39  is constituted as  FIG. 1 , the papers are automatically arranged sequentially from the first page, because the papers are stacked on the outputting stack portion  39  with the image plane facing downward. After the image is transferred from the intermediate transfer belt  11  to the paper P, remaining toner and a paper powder are cleaned by the cleaning unit  15  including the cleaning blade  16  inside from the belt surface, and are collected.  
         [0052]     In this embodiment, the image is formed on only one side of the paper, but it is possible to constitute an image forming apparatus to form images on both sides of the paper by configuring the second transferring unit  30  as a second intermediate transfer belt. When images are formed in both sides of paper P, a four-color overlaid toner image formed as the first image carried on the surface of the intermediate transfer belt  11  is transferred to the second intermediate transfer belt  30  by the second transferring roller  34 .  
         [0053]     After that, while another four-color overlaid toner image is being formed as the second image on the intermediate transfer belt  11 , the first image is transported to a transfer point by the second intermediate transfer belt  30 .  
         [0054]     The first image and the second image are transferred to the both sides of paper at the same time by taking timing of the intermediate transfer belt  11 , the second intermediate transfer belt and the resisting roller pair  28 .  
         [0055]     The paper P holding the toner image on the both sides of surface of itself is transported to the fixing device  36  and the both images are fixed at the same time. Then, the paper is transported through the outputting guide  37 , and outputted to the outputting stack portion  39  by the outputting roller  38 .  
         [0056]     In this embodiment, an image forming apparatus forms a color toner image by using a plurality of toner, but it is possible to constitute an image forming apparatus to form a monochrome image by using a black toner.  
         [0057]     A way of attachment and detachment of the intermediate-transferring unit  20  from the main body of the image forming apparatus is explained as follows.  
         [0058]      FIG. 2  is a perspective view showing a frame constitution of the main body of the image forming apparatus.  
         [0059]     As shown in this figure, the frame of the main body includes a front faceplate  41 , a rear faceplate  42 , a side plate  43  configured to connect the front faceplate  41  and the rear faceplate  42 , and a bottom plate  44 .  
         [0060]     In addition, a left guide rail  45  and a right guide rail  46  configured to support the intermediate transferring device  10  detachable are fixed between the front faceplate  41  and the rear faceplate  42 . An upper opening  41   a  and a lower opening  41   b  are placed in the front faceplate  41 .  
         [0061]     The intermediate transferring unit  20  including the intermediate transferring device  10  and the cleaning unit  15 , and each image forming unit SU can be attached to and detached from the main body of the image forming apparatus through the upper opening  41   a.    
         [0062]     A photoconductor fixing plate  47  configured to open and close the upper opening  41   a  is fixed to the front faceplate  41  and rotates around an axis. The paper feeding cassette  26 - 1 ,  26 - 2  can be attached to and detached from the main body of the image forming apparatus through the lower opening  41   b.    
         [0063]     A driving device  48  is attached to the rear faceplate  42 . The driving device  48  includes motors and gear alignments configured to drive driving rollers of the photoconductor drum  1 , the developing device  5  in the image forming unit SU and the intermediate transfer belt  11 .  
         [0064]      FIG. 3  is a perspective view showing the intermediate transferring unit  20  when the intermediate transferring unit  20  is supported by the guide-rails  45 ,  46  in right and left.  
         [0065]     In this Figure, the frame of the main body is omitted for illustration purposes. The intermediate transferring unit  20  including the intermediate transferring device  10  and the cleaning unit  15  is supported by the guide rails  45 ,  46  in right and left, and is removable from the main body of the apparatus together. A pair of handles  23  is disposed on the top surface of the intermediate-transferring device  10 . These handles  23  are capable of being folded. When the intermediate transferring device  10  or the intermediate transferring unit  20  is drawn from the main body of the image forming apparatus, the handles  23  can be held by hands by drawing them as shown in the  FIG. 3 . And when the intermediate transferring device  10  or the intermediate transferring unit  20  is inserted in the main body of the image forming apparatus, the handles  23  can be folded along the top surface of the intermediate transferring device  10 .  
         [0066]     As mentioned before, the intermediate transferring device  10  (the intermediate transferring unit  20 ) is supported by the guide rails  45 ,  46  in right and left, and is removable from the main body of the image forming apparatus.  
         [0067]     As shown in  FIG. 4 , a locking device configured to control removal of the intermediate transferring device  10  (the intermediate transferring unit  20 ) is installed in the intermediate transfer point  10  (the intermediate transferring unit  20 ). A locking lever  52  is fixed in front end of a shaft  51  that is supported by and through the intermediate transferring device  10  and that rotates with the shaft  51 . A locking member  53  is fixed in rear end of the shaft  51 . Triangle-shaped protruding portion  53   a  is formed in the locking member  53 . As shown in  FIG. 4 ( a ), when an arm of the locking lever  52  is in a horizontal position, locking state is cancellation. Then, the triangle-shaped protruding portion  53   a  of the locking member  53  is approximately positioned overhead. On the contrary, as shown in  FIG. 4 ( b ), when the locking lever  52  is turned 90 degrees counterclockwise, the triangle-shaped protruding portion  53   a  of the locking member  53  protrudes to left side.  
         [0068]     As shown in  FIG. 5 , an insert portion  42   a,  which the locking member  53  can get into, is formed in the rear faceplate  42  of the frame of the main body. When the intermediate transferring device  10  (the intermediate transferring unit  20 ) is installed toward the depths of the main body of the image forming apparatus, the locking member  53  reaches to behind of the rear faceplate  42  through the insert portion  42   a.  When the locking lever  52  is in a state as shown in  FIG. 4 ( a ), the relationship of the locking lever  52  and the fixing plate  42  is shown in  FIG. 5 ( a ). As shown in  FIG. 5 ( a ), because the locking members  53  is not locked in the rear faceplate  42 , the intermediate transferring device  10  (the intermediate transferring unit  20 ) can be removal from the main body of the image forming apparatus.  
         [0069]     When the locking lever  52  is turned as shown in  FIG. 4 ( b ) in the state that the intermediate transferring device  10  (the intermediate transferring unit  20 ) is inserted in to the depths of the main body of the image forming apparatus, the locking member  53  also rotates as shown in  FIG. 5 ( b ). Then, the triangle-shaped protruding portion  53   a  of the locking member  53  gets into the behind of the rear faceplate  42 .  
         [0070]     In this state, the intermediate transferring device  10  (the intermediate transferring unit  20 ) can not be withdrawn from the main body of the image forming apparatus, because the triangle-shaped protruding portion  53   a  of the locking member  53  is locked in the rear faceplate  42 .  
         [0071]     In addition, when the locking lever  52  is in the locking released state as shown in  FIG. 4 ( a ), the photoconductor fixing plate  47  can be opened, because an arm member  52   a  of the locking lever  52  is not locked in the photoconductor fixing plate  47 . When the photoconductor fixing plate  47  is opened, as mentioned before, the intermediate transferring unit  20  supported by the guide rails  45 ,  46  in right and left is removable from the main body of the image forming apparatus. The intermediate transferring device  10  and the cleaning unit  15  is removable together from the main body of the image forming apparatus. In addition, when a locking device for the cleaning unit (not shown) is removed, the cleaning unit  15  can be detached from the main body of the image forming apparatus independently. Also, each of the image-forming units SU can be removed by opening the photoconductor fixing plate  47 .  
         [0072]     When the photoconductor fixing plate  47  is closed and the locking lever  52  is in the locked condition (so that the locking lever  52  is disposed in lengthwise direction as shown in  FIG. 4 ( b )), the photoconductor fixing plate  47  is also locked because of the arm member  52   a  of the locking lever  52  presses the photoconductor fixing plate  47 . Thus, the intermediate transferring unit  20  is locked also. Also, removal of the image-forming unit SU is not possible.  
         [0073]     A rear protruding portion  53   b  of the locking member  53  and a sensor  54  are constituted to be able to detect that the intermediate transferring device  10  (the intermediate transferring unit  20 ) is inserted to the depths of the main body of the image forming apparatus, and it is locked. For example, a photo-interrupter having a light emitting member and a light receiving member can be used as the sensor  54 .  
         [0074]     In this example, the rear-protruding portion  53   b  of the locking member  53  is formed in the shape of a plate. In the locking released state as shown in  FIG. 4 ( a ), the rear-protruding portion  53   b  of the locking member  53  entered in a detection area of the sensor  54  can not interrupt the light from the light emitting member as shown in  FIG. 4 ( c ). On the contrary, in the locking state as shown in  FIG. 4 ( b ) with the locking lever  52  turning, the rear-protruding portion  53   b  of the locking member  53  interrupts the light from the light-emitting member as shown in  FIG. 4 ( d ). By this embodiment, locking of the intermediate-transferring device  10  (the intermediate transferring unit  20 ) is detected. Thus, this detects the intermediate transferring device  10  (the intermediate transferring unit  20 ) is set in the main body of the image forming apparatus. When the sensor  54  does not detect a set (a lock) of the intermediate-transferring device  10  (the intermediate transferring unit  20 ), at least, the image forming apparatus is controlled not to form an image.  
         [0075]     In addition to the constitution explained above, a microswitch and other sensing mechanisms could be adopted as the sensor.  
         [0076]     In addition, a front cover (not shown) is installed in an outer casing of the image forming apparatus. When the front cover is opened, a front portion of the frame of the device is exposed, and operation of the locking lever  52  and opening of the photoconductor fixing plate  47  are enabled. In addition, exclusive doors can be provided with the outer casing corresponding to the locking lever  52  and the photoconductor fixing plate  47 .  
         [0077]     In this example, as mentioned before, the intermediate transferring device  10  and the cleaning unit  15  can be attached to and detached from the main body of the image forming apparatus together as the intermediate transferring unit  20 . It is possible to constitute the cleaning unit  15  that can be removal from the main body of the image forming apparatus separately while the intermediate transferring device  10  is remaining in the main body of image forming apparatus. When the cleaning unit  15  can be detachable from the main body of the image forming apparatus independently of the intermediate transferring device  10 , maintenance work becomes easier because a plurality of devices can be easily attached to and detached from the main body of the image forming apparatus. Often, the life of the cleaning member (for example, cleaning blade  16 ) is shorter than that of an intermediate transfer belt. Thus, with this embodiment, when the cleaning unit  15  reaches its life, it is not necessary to change the intermediate transferring unit  20  or the intermediate transferring device  10 . When the cleaning unit  15  can be removed from the intermediate transferring device  10  after removing the intermediate transferring unit  20  from the main body of the image forming apparatus, the cleaning unit  15  is easily removed from the intermediate transferring device  10  by adopting the rail mechanism. In addition, because the attachment and detachment direction of the intermediate transferring unit  20  is parallel to a rotation shaft of the intermediate transfer belt  11 , the constitution detachably supporting the intermediate transferring unit  20  (e.g., the guide rail) is simplified.  
         [0078]     A mechanism of attachment and detachment of the second transferring unit  30  (the transfer roller  34 ) is explained next. As shown in  FIG. 6 , the second transferring cover  40  configured to support the second transferring unit  30  is possible to rotate and open around the shaft  24 . And when a paper jam occurs, the second transferring cover  40  may be opened to remove the paper from the path of paper transportation.  
         [0079]      FIG. 7  and  FIG. 8  both show a state where the second transferring cover  40  is closed.  FIG. 7  shows a closed cover when the image forming apparatus is in a non-image forming state, such as a waiting state.  FIG. 8  shows a closed cover when the image forming apparatus is in an image forming state. In the non-image forming state, cam member  60  presses a second transferring unit removing lever  61  in a direction to right in  FIG. 7  so as to rotate the second transferring unit  30  around an rotation axis  62 . Thus, the second transferring roller  34  is removed from the intermediate transfer belt  11 . In the image forming state, the cam member  60  turns a half turn and rotates the second transferring unit  30  around the rotation axis  62  toward the intermediate transferring unit  20 . Thus, the second transferring roller  34  is placed in contact with the intermediate transfer belt  11  by the pressing of a pressing member such as a spring attached to the second transferring cover  40 .  
         [0080]     The mechanism for placing the second transferring unit  30  in and out of contact with the intermediate transferring unit  20  when the second transferring cover  40  is closed with cam member  60  and the second transferring unit removing lever  61  is shown in more detail in  FIG. 9 . As shown in  FIG. 9 , rotation of the cam member  60  is performed by engaging of a gear  67  attached to a cam shaft  66  with a gear  68 , and engaging of the gear  68  with a worm gear  69  connected to a motor  70 . When the motor  70  is not energized in the non-image forming state, as shown in  FIG. 7 , the second transferring roller  34  removes from the intermediate transfer belt  11  by pressing of the cam member to the second transferring unit removing lever  61 . By this mechanism, when the intermediate transferring unit  20  is detached from the main body of the image forming apparatus, the second transferring roller  34  cannot be contacted with the intermediate transfer belt  11 . When the motor  70  is energized in the image forming state, as shown in  FIG. 8 , the second transferring roller  34  contacts with the intermediate transfer belt  11  by turning of the cam member in a half round. By this mechanism, an image on the intermediate transfer belt  11  can be transferred to a paper.  
         [0081]     It is also possible to adopt a reverse constitution that the motor  70  is energized in the non-image forming state and then the cam member  60  turns in a half round to remove the second transferring roller  34  from the intermediate transfer belt  11 .  
         [0082]     The construction of the present invention is not limited to the previously described and illustrated embodiments. For example, a tensioned shape of the intermediate transfer belt or the transportation belt (a transfer belt) may be used, with the constitution of the guide rail set appropriately. In addition, the cleaning device is not limited to a cleaning blade but may also include a cleaning roller or a cleaning brush. Also, alternative types of image forming units or fusing devices may be used.  
         [0083]     The preceding apparatus may be a printer, a facsimile, a copier or another type of image forming apparatus.  
         [0084]     Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.