Patent Publication Number: US-7907867-B2

Title: Creep resistant cleaning device and image forming device having the same

Description:
RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2005-377434, the content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a cleaning device for an intermediate transfer body for use in an image forming apparatus for forming images with use of the intermediate transfer body. 
     Known as one of the conventional electrophotographic image forming apparatuses is an image forming apparatus in which a developer image formed on a photoreceptor is primarily transferred onto an intermediate transfer body and then the developer image is secondarily transferred from the intermediate transfer body to a paper sheet. Such an image forming apparatus normally has a cleaning device for removing undesired substances such as residual developers on the intermediate transfer body after the secondary transfer as well as paper powders and dust attached onto the surface of the intermediate transfer body. 
     The cleaning device is typified by those removing the residual developer and the like by bringing a metal or rubber blade into pressure contact with the surface of the intermediate transfer body. In order to cope with the case where such a blade cannot provide a sufficient cleaning effect or the case where it is necessary to remove a so-called separation streak, which are a streak formed by a residual developer having been already collected by the blade when the blade is separated from the intermediate transfer body, a technology for placing a seal member serving as another cleaning member on the surface of the intermediate transfer body on the downstream side of the blade with respect to the moving direction has been proposed. 
     However, the conventional technology for placing the seal member on the downstream side of the blade has such a problem that the seal member suffers creep deformation with the elapse of time and this hinders fulfillment of a sufficient cleaning effect. 
     Moreover, a cleaning device having a seal member placed on the upstream side of a blade, which has been disclosed in U.S. Pat. No. 5,991,568, is not capable of cleaning the separation streak remaining when the blade is separated from the intermediate transfer body. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a cleaning device capable of maintaining a sufficient cleaning effect by preventing creep deformation of the cleaning member. 
     In order to accomplish the object, the cleaning device of the present invention for cleaning a transfer body in an image forming apparatus includes: a first cleaning member whose top end is brought into pressure contact with the transfer body; and a second cleaning member which is placed downstream from the first cleaning member with respect to a moving direction of the transfer body and whose top end is brought into pressure contact with the transfer body, wherein the second cleaning member is provided rotatably with respect to the first cleaning member. 
     Moreover, an image forming apparatus of the present invention includes: a transfer body for retaining an image formed with a developer; and a cleaning device for cleaning the transfer body, wherein the cleaning device includes: a first cleaning member whose top end is brought into pressure contact with the transfer body; and a second cleaning member which is placed downstream from the first cleaning member with respect to a moving direction of the transfer body so at to be rotatable with respect to the first cleaning member and whose top end is brought into pressure contact with the transfer body. 
     According to the cleaning device and the image forming apparatus having the same in the present invention, the second cleaning member disposed downstream from the first cleaning member is rotatably provided, so that creep deformation of the second cleaning member can be prevented and sufficient cleaning performance can be maintained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be further described with reference to the accompanying drawings wherein like reference numerals refer to like parts in the several views, and wherein: 
         FIG. 1  is a schematic structure view showing an image forming apparatus having a cleaning device in one embodiment of the present invention; 
         FIG. 2  is a perspective view showing an intermediate transfer unit structured so as to integrally include an intermediate transfer belt and a cleaning device; 
         FIG. 3  is a side view showing a positional relation between the intermediate transfer belt and the cleaning device; 
         FIG. 4  is a view showing the cleaning device separated from the intermediate transfer belt; 
         FIG. 5A  is a view showing the structure of a conventional cleaning device; 
         FIG. 5B  is a view showing a second cleaning member in the conventional cleaning device deflected and deformed upon coming into contact with the intermediate transfer belt; 
         FIG. 6A  is a view showing the state immediately after the conventional cleaning device starts to be separated from the intermediate transfer belt and before the second cleaning member is creep-deformed; 
         FIG. 6B  is a view showing the state immediately after the conventional cleaning device starts to be separated from the intermediate transfer belt and after the second cleaning member has been creep-deformed; 
         FIG. 7A  is a view showing the state that the conventional cleaning device is completely separated from the intermediate transfer belt and before the second cleaning member is creep-deformed; 
         FIG. 7B  is a view showing the state that the conventional cleaning device is completely separated from the intermediate transfer belt and after the second cleaning member has been creep-deformed; 
         FIG. 8  is a view showing a cleaning device in one embodiment of the present invention; 
         FIG. 9A  is a side view showing a rotation and pressing mechanism of a second cleaning member in the cleaning device; 
         FIG. 9B  is a perspective view showing the rotation and pressing mechanism of the second cleaning member in the cleaning device; 
         FIG. 9C  is a perspective view of the rotation and pressing mechanism of the second cleaning member in the cleaning device shown with a first cleaning member being omitted; 
         FIG. 10A  is a view showing an example of a size of each cleaning member in the cleaning device; 
         FIG. 10B  is a view showing an example of a rotation angle of the second cleaning member in the cleaning device; 
         FIG. 11  is a view showing the state immediately after the cleaning device starts to be separated from the intermediate transfer belt; 
         FIG. 12  is a view showing the state that the cleaning device is completely separated from the intermediate transfer belt; 
         FIG. 13  is a view showing a positional relation when each cleaning member of the cleaning device is away from the intermediate transfer belt; 
         FIG. 14  is a timing chart of an image forming apparatus having the cleaning device in one embodiment of the present invention; and 
         FIG. 15  is a block diagram showing the image forming apparatus having the cleaning device in one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows an overall schematic structure of an image forming apparatus  10  having a cleaning device  30  in one embodiment of the present invention. The image forming apparatus  10  has a roller-shaped photoreceptor rotationally driven in an arrow A direction in almost the center of the inside of the apparatus. Placed adjacent to the photoreceptor  12  is an almost column-shaped developing unit  14  which is rotationally driven in an arrow B direction. 
     The developing unit  14  is composed of four developing devices  16 Y,  16 M,  16 C,  16 K corresponding respectively to toner (developer) of yellow (Y), magenta (M), cyan (C) and black (K) colors, the developing devices being disposed evenly in circumferential direction around the developing unit  14 . Each of the developing devices  16 Y,  16 M,  16 C,  16 K has a developing roller  18  for feeding the toner held on its outer circumferential face while rotating for developing an electrostatic latent image on the surface of the photoreceptor  12 . 
     Moreover, disposed around the photoreceptor  12  are a charging device  20  for uniformly charging the surface of the photoreceptor  12 , an exposure device  22  for exposing the uniformly charged surface of the photoreceptor  12  in conformity with image data so as to form an electrostatic latent image, and a primary transfer roller  26  for primarily transferring a toner image formed by developing the electrostatic latent image with the developing unit  14  from the photoreceptor  12  to an intermediate transfer belt (transfer body)  24 . It is to be noted that without being limited to the belt shape, the transfer body may take other shapes (e.g., a roller shape). 
     The intermediate transfer belt  24 , which is an endless belt like an endless sheet, is supported by four rollers including the primary transfer roller  26  disposed inside the belt and is rotationally driven in an arrow C direction in the state that specified tension is applied. Moreover, a secondary transfer roller  28  for secondarily transferring a toner image, which has been transferred onto the intermediate transfer belt  24 , onto a paper sheet is placed on the outer peripheral face of the intermediate transfer belt  24  in the state of being in contact therewith. Further, a cleaning device  30  for removing undesired substances such as residual toner on the surface of the intermediate transfer belt  24  after the secondary transfer as well as paper powders and dust attached onto the surface is provided on the intermediate transfer belt  24  in a separatable way. Detailed description of the cleaning device  30  will be given later. 
     A paper feed section  50  for housing paper sheets that are recording media is provided on the lower side in the image forming apparatus  10 . The paper sheets housed in the paper feed section  50  are sent out one by one by a paper feed roller  52 . A paper sheet sent out from the paper feed section  50  is transported upward by a pair of transportation rollers  54 , and is feed into between the intermediate transfer belt  24  and the secondary transfer roller  28  by a pair of timing rollers  56  in a specified timing that a toner image transferred onto the intermediate transfer belt  24  is transported to a position in contact with the secondary transfer roller  28 . 
     Moreover, inside the image forming apparatus  10 , a fixing device  58  is placed above the secondary transfer roller  28 , and a paper discharge section  60  is provided in an upper part of the image forming apparatus  10 . Further, on a main body of the image forming apparatus  10 , a display section (unshown) formed from, for example, an LCD for displaying various information is placed. 
     It is to be noted that the image forming apparatus  10  may have a double-sided unit for allowing automatic image formation on both sides of a paper sheet, an additional paper feed cassette for housing a large number of or a wide variety of paper sheets, and a manual feeder mechanism. 
     Description is now given of image forming operation of the above-structured image forming apparatus  10 . 
     The image forming apparatus  10  starts image forming operation upon reception of image data from a computer connected directly or via a network. 
     In the case where the image data is a color image, a yellow electrostatic latent image formed on the surface of the photoreceptor  12  by the exposure device  22  is first developed by the developing device  16 Y to form a yellow toner image, and the yellow toner image is primarily transferred from the photoreceptor  12  onto the intermediate transfer belt  24 . Next, in the same process, while the developing unit  14  is rotated, a magenta toner image, a cyan toner image and a black toner image are formed in succession and are primarily transferred in sequence to be superimposed on the yellow toner image having been transferred on the intermediate transfer belt  24 . In this case, the intermediate transfer belt  24  is rotated at least four times, during which the cleaning device  30  is in the state away from the intermediate transfer belt  24 , and therefore four color toner images are not scraped away by the cleaning device  30 . 
     The toner images transferred in the state of being superimposed on the intermediate transfer belt  24  are transported by rotation of the intermediate transfer belt  24  to a position in contact with the secondary transfer roller  28 . At this point, a paper sheet sent out from the paper feed section  50  by the paper feed roller  52  and transported upward by a pair of the transportation rollers  54  and a pair of the timing rollers  56  is fed into a contact section between the intermediate transfer belt  24  and the secondary transfer roller  28 . As a result, the toner image on the intermediate transfer belt  24  is secondarily transferred onto the paper sheet due to an electrostatic action by the secondary transfer roller  28 . Residual toner and undesired substances on the intermediate transfer belt  24  after the secondary transfer are removed by the cleaning device  30  which is in contact with the intermediate transfer belt  24 . 
     Then, when the paper sheet with the toner image transferred thereupon passes the fixing device  58 , in which the toner image is fixed by heat and pressure, and then the paper sheet is discharged to the paper discharge section  60 . 
     In the case where the image data is a monochrome image (a black image in particular), a toner image is formed by using one developing device of corresponding color, and a monochrome image is attained by the same process as described above (i.e., primary transfer onto the intermediate transfer belt  24 , secondary transfer from the intermediate transfer belt  24  to a paper sheet, fixation of a toner image and so on). In this case, the monochrome image primarily transferred onto the intermediate transfer belt  24  is secondarily transferred onto a paper sheet immediately, and therefore the intermediate transfer belt  24  should only be rotated one time and the cleaning device  30  should kept in contact with the intermediate transfer belt  24  without the necessity of being separated therefrom. 
     Detailed description is now given of the cleaning device  30 . 
       FIG. 2  is an external perspective view showing an intermediate transfer unit  31  structured so as to integrally include the intermediate transfer belt  24  hung over four rollers and the cleaning device  30 . The intermediate transfer unit  31  receives drive from the main body in the state of being mounted inside the main body of the image forming apparatus  10 . 
     The cleaning device  30  is in pressure contact with the intermediate transfer belt  24  by a plurality of (two in this embodiment) tension coil springs  32 . This is for pressing an unshown cleaning member in the cleaning device  30  toward the intermediate transfer belt  24  with constant pressure, and detail thereof will be described later. 
     Moreover, as described in the image forming operation, the cleaning device  30  needs to be able to move so as to be in pressure contact with and be separated from the intermediate transfer belt  24 . During color image formation, the intermediate transfer belt  24  needs to be rotated four times so as to superimpose four color toner images, and in this operation, the cleaning member should be away from the intermediate transfer belt  24 . At any other time, the cleaning member is in pressure contact with the intermediate transfer belt  24 . 
     In consideration of the moving velocity of the intermediate transfer belt  24 , the size of the image forming apparatus  10  and the length of the intermediate transfer belt  24  determined based on various image processes, the pressure contact/separation operation of the cleaning device  30  should be performed smoothly and swiftly. In the present embodiment, a reciprocating motion of a pressure contact/separation shaft  33  is converted to a rotational motion of the cleaning device  30  so as to perform the pressure contact/separation operation of the cleaning device  30 . The reciprocating motion of the pressure contact/separation shaft  33  is controlled by a drive member on the main body side of the image forming apparatus  10 . A coupling member (unshown) is mounted on an end section  33   a  of the pressure contact/separation shaft  33  opposite to an end section in contact with the cleaning device  30 , and the coupling member and a drive member on the main body side are engaged and operated together in the state that the intermediate transfer unit  31  is mounted in the image forming apparatus  10 . 
       FIG. 3  is a side view showing a positional relation between the intermediate transfer belt  24  and the cleaning device  30  in  FIG. 2 . The intermediate transfer belt  24  moves in an arrow C direction by rotation of a drive roller  34 . In order to determine the shape of the intermediate transfer belt  24 , an opposition roller  35 , a primary transfer roller  26  and a tension roller  36  for applying constant belt tension are disposed. 
       FIG. 4  shows the state that the cleaning device  30  is separated from the intermediate transfer belt  24 . The cleaning device  30  rotates counterclockwise around a rotation center  37  as a supporting point so that components in the cleaning device  30  are away from the intermediate transfer belt  24  by a constant distance. 
     Description is now given of the detailed structure and operation of the cleaning device  30  in comparison to a conventional cleaning device  30 ′ with reference to  FIG. 5A  through  FIG. 13 . 
       FIG. 5A  shows the state that the conventional cleaning device  30 ′ is in pressure contact with the intermediate transfer belt  24 . An arrow C represents a moving direction of the intermediate transfer belt  24 . The cleaning device  30 ′ is in pressure contact with the intermediate transfer belt  24  by tension coil springs  32  (see  FIG. 2 ). 
     The cleaning device  30 ′ has a first cleaning member  38  and a second cleaning member  39  placed downstream from the first cleaning member  38  with respect to the moving direction of the intermediate transfer belt  24 . As the first cleaning member, a blade member made of, for example, an urethane rubber or metal is used. As the second cleaning member, for example, a urethane sheet bonded to a resin sheet is used. The second cleaning member  39  is placed in the state of being fixed so as not to be rotated at a specified position with respect to the first cleaning member  38 . Moreover, the first cleaning member  38 , which is rotatable around a supporting point  40 , is pressed by the tension coil springs  32  (see  FIG. 2 ) so as to keep pressure applied to the intermediate transfer belt  24  constant. 
     The cleaning device  30 ′ shown in  FIG. 5A  is in a pressure contact state, i.e., under cleaning operation, and a top end section of the first cleaning member  38  is removing residual toner and the like on the intermediate transfer belt  24 . The removed toner and the like are entered inside a housing  41  and is processed so that the removed toner and the like will not splatter out of the cleaning device  30 . In this case, the second cleaning member does not particularly operate. While  FIG. 5A  shows that the second cleaning member  39  extends straight as with the state not in contact with the intermediate transfer belt  24  (hereinbelow referred to as “initial state”), the second cleaning member  39  in actuality is deflected and deformed upon coming into contact with the intermediate transfer belt  24  and being pressed thereby. That state is shown in  FIG. 5B . Since the cleaning device  30 ′ is often retained in the state shown in  FIG. 5B , out of concern of the creep deformation, a thin sheet type member less prone to creep deformation is used as the second cleaning member  39 . 
       FIG. 6A  shows the state that the conventional cleaning device  30 ′ has been finished cleaning and the cleaning device  30 ′ starts to be separated from the intermediate transfer belt  24 . Immediately after the first cleaning member  38  is separated from the intermediate transfer belt  24 , the second cleaning member  39  is still in contact with the intermediate transfer belt  24 , and therefore a so-called separation streak, which are a streak formed by residual toner and the like having been already collected when the first cleaning member  38  is separated, can be removed by the second cleaning member  39 . The second cleaning member  39  also plays a role of removing not only the separation streak but also all the residual toner that the first cleaning member  38  has failed to scrape. An electricity removal seal member is sometimes provided in the vicinity of the upstream side of the first cleaning member  38 , and in the case where the first cleaning member  38  fails to remove the separation streak of the seal member, the second cleaning member  39  is to remove it. 
       FIG. 6A  shows that the second cleaning member  39  is in the initial state so that its top end section is lightly in pressure contact with the intermediate transfer belt  24  without suffering deflection and deformation. When the second cleaning member  39  is left in the state shown in  FIG. 5B  for a longer period of time, the second cleaning member  39  suffers creep deformation. 
       FIG. 6B  shows an example of the case where the second cleaning member  39  suffers creep deformation. Although the second cleaning member  39  should essentially be pressed toward the intermediate transfer belt  24  to remove the separation streak of the first cleaning member  38 , progress of the creep deformation causes the second cleaning member  39  to be separated from the intermediate transfer belt  24  almost concurrently with the first cleaning member  38 . 
     The second cleaning member  39  is aligned with the first cleaning member  38  in a certain standard value range and fixed. The standard value is determined in consideration of a moving velocity of the intermediate transfer belt  24  and a moving (rotation) velocity of the cleaning device  30 ′ so that the second cleaning member  39  can remove the separation streak generated when the first cleaning member  38  is separated from the intermediate transfer belt  24 . Therefore, once the creep deformation of the second cleaning member  39  has progressed beyond a certain degree, the separation streak of the first cleaning member  38  cannot be removed. Toner and the like that constitute the unremoved separation streak are likely to fall during movement of the intermediate transfer belt  24 , and may soil the inside of the image forming apparatus  10  or may be reattached to other positions of the intermediate transfer belt  24  and be transferred onto a paper sheet, resulting in degradation of image quality. 
     It may be considered to allow a sufficient length for the second cleaning member  39  so that the separation streak can be removed even with creep deformation of the second cleaning member  39 . In this case, however, the cleaning device  30 ′ grows in size, and this contradicts downsizing of the image forming apparatus  10 . 
       FIGS. 7A and 7B  show the state that the cleaning device  30 ′ is completely separated from the intermediate transfer belt  24 .  FIG. 7A  shows an example in which the second cleaning member  39  is in the initial state, while  FIG. 7B  shows an example in which the second cleaning member  39  suffers creep deformation. The removed toner is attached to the first cleaning member  38  and the second cleaning member  39 , and separating these members from the intermediate transfer belt  24  by a specified distance prevents the toner from splattering. 
       FIG. 8  shows the state that the cleaning device  30  in the present embodiment is in pressure contact with the intermediate transfer belt  24 . As with the above-stated cleaning device  30 ′, the cleaning device  30  also has a first cleaning member  38  and a second cleaning member  39  placed downstream from the first cleaning member  38  with respect to the moving direction of the intermediate transfer belt  24 , though the cleaning device  30  is different from the cleaning device  30 ′ in the point that the second cleaning member  39  is provided rotatably with respect to the first cleaning member  38 . 
     The second cleaning member  39  is rotatable around a rotation center  42  as a supporting point. The rotation center  42  may be positioned with respect to the first cleaning member  38  or the housing  41 . 
     In the case where the second cleaning member  39  is positioned with respect to the first cleaning member  38 , it becomes relatively easy to secure a positional relation therebetween during assembling process. In this case, it is necessary to secure a space to mount the second cleaning member  39  in a part of the components supporting the first cleaning member  38 . Moreover, the first cleaning member  38  is slightly influenced by elastic deformation due to pressure contact of the first cleaning member  38  with the intermediate transfer belt  24 . In the case where the positional displacement of the rotation center  42  or an inclination of a support shaft including the rotation center  42  are generated because of the elastic deformation, assembling operation should be performed on the assumption that the elastic deformation would occur. 
     In the case where the second cleaning member  39  is positioned with respect to the housing  41 , it is necessary to secure a positional relation between the first cleaning member  38  and the second cleaning member  39  on the housing  41  side. Since both the members are separately mounted on the housing  41 , it becomes necessary to secure assembling accuracy based on component accuracy, to employ a structure allowing assembling with use of jigs and to provide a mechanism allowing position adjustment. Once the positioning and assembly are completed, an influence of bringing the first cleaning member  38  into pressure contact with the intermediate transfer belt  24  is eliminated and therefore it is unnecessary to concern this point during assembling process. 
     In the case where the second cleaning member  39  is not positioned with respect to the first cleaning member  38  and the housing  41 , a plurality of members are to be interposed and this makes it difficult to secure the positional relation between these members. If the positional relation is not secured, then an advantage obtained by making the second cleaning member  39  rotatable cannot be fully utilized. 
     As with the above-stated conventional cleaning device  30 ′, the entire cleaning device  30  is biased toward the intermediate transfer belt  24  by tension coil springs  32  (see  FIG. 2 ), and the intermediate transfer belt  24  moves in an arrow C direction. The first cleaning member  38 , which is rotatable around a supporting point  40 , is pressed by the tension coil springs  32  so as to keep pressure applied to the intermediate transfer belt  24  constant. 
     The cleaning device  30  shown in  FIG. 8  is in a pressure contact state, i.e., under cleaning operation, and a top end section of the first cleaning member  38  is removing residual toner and the like on the intermediate transfer belt  24 . The removed toner and the like are entered inside the housing  41  and is processed so that the removed toner and the like will not splatter out of the cleaning device  30 . In this case, the top end of the second cleaning member  39  is lightly in pressure contact with the intermediate transfer belt  24 . 
       FIGS. 9A to 9C  shows a pressing mechanism for bringing the second cleaning member  39  into pressure contact with the intermediate transfer belt  24 , and  FIG. 9A  is a view of the pressing mechanism seen from the opposite direction of  FIG. 8 . A mounting member  43  of the second cleaning member  39  is bonded and fixed to the first cleaning member  38 . The second cleaning member  39  is bonded and fixed to a support member  44 . The support member  44  is rotatably supported by the mounting member  43  at the position of the rotation center  42 . This makes the second cleaning member  39  rotatable with respect to the first cleaning member  38 . Moreover, the second cleaning member  39  is rotatable in the range free from generation of creep deformation when the first cleaning member  38  is brought into pressure contact with the intermediate transfer belt  24 . “The range free from generation of creep deformation” herein refers to a rotation range including a position at which stress applied to the top end of the second cleaning member  39  in a bending direction is equal to or less than a limit value for preventing creep deformation of the second cleaning member  39 . The “limit value” may herein be attained by following process. The stress in the bending direction is applied to the top end of the second cleaning member  39 , and the second cleaning member  39  is left under a temperature condition of 35° C. for 100 hours. Consequently, when the stress is removed from the second cleaning member  39 , such deformation that the direction of the top end section of the second cleaning member  39  bends approx 5 degrees from the initial state (i.e., such deformation that a variation in the bending direction of the top end position of the second cleaning member  39  is approx. 9% of a free length of the second cleaning member  39 ) is caused. The stress value when such deformation remains may be referred to as the limit value. In other words, if the variation under this condition is less than 5 degrees, then the stress in this case is within the level free from generation of creep deformation of the second cleaning member  39 , and the rotation position of the second cleaning member  39  exposed to such stress is in “the range free from generation of creep deformation” (provided that numerical values used herein are only one example and that the present embodiment is not limited to these numerical values). 
     By setting torsion coil springs  45  around the support shaft including the rotation center  42 , the second cleaning member  39  is biased toward an arrow D direction (i.e., toward the intermediate transfer belt  24 ). While the position of the top end of the second cleaning member  39  is regulated by the intermediate transfer belt  24 , a rotation regulation member is necessary in order to secure a specified position in the state that the cleaning device  30  is separated from the intermediate transfer belt  24  and the second cleaning member  39  is free from regulation by the intermediate transfer belt  24 . In this embodiment, the mounting member  43  also serves as the rotation regulation member. More particularly, by bringing an end section  43   a  of the mounting member  43  into contact with an extension section  44   a  of the support member  44  for the second cleaning member  39 , rotation of the second cleaning member  39  is regulated in the state that the second cleaning member  39  is almost parallel to the first cleaning member  38 . 
       FIGS. 9B and 9C  are perspective views showing the structure shown in  FIG. 9A , and  FIG. 9C  shows the structure with the first cleaning member  38  removed. A support section for supporting the second cleaning member  39  rotatably with respect to the first cleaning member  38  is provided in two positions in the longitudinal direction of the second cleaning member  39 . This is for uniformly applying biasing power by a spring  45  and for securing a large distance between supporting points to secure positional accuracy. It is to be noted that the support section may be provided in three or more positions in consideration of deformation in the longitudinal direction of the second cleaning member  39  or for the purpose of changing the way the biasing force is applied. 
     If the biasing force by the torsion coil springs  45  is excessively large, then a sufficient advantage cannot be implemented even with the rotatable structure of the second cleaning member  39  due to deflection and deformation as with the conventional cleaning device  30 ′. Although biasing force equal to or less than the limit quantity for preventing creep deformation of the second cleaning member  39  is applied in the present embodiment, creep deformation may be allowed to some degree if there is some structural allowance. Herein “the limit quantity for preventing creep deformation” refers to biasing force which causes the stress of the limit value as described above to be applied to the top end of the second cleaning member  39 . In determining the biasing force of the torsion coil spring  45 , sufficient results may be expected by setting the limit quantity to be equal to or lower than a stress limit for creep deformation in consideration of a stress value applied to the second cleaning member  39 . 
       FIGS. 10A and 10B  show one example of a size of each section. In  FIG. 10A , the second cleaning member  39  opened to a rotation regulation position is overlapped with the intermediate transfer belt  24 . A reference character “r” represents a distance between top ends of the first cleaning member  38  and the second cleaning member  39 , a reference character “q” represents a free length of the second cleaning member  39  and a reference character “p” represents an overlapping margin of the second cleaning member  39  and the intermediate transfer belt  24 .  FIG. 10B  shows the rotating state of the second cleaning member  39  with a rotation angle “θ” made when the second cleaning member  39  in the state shown in  FIG. 10A  rotates till its top end comes into contact with the intermediate transfer belt  24  without deflection and deformation. In the present embodiment, an urethane sheet with a thickness of 150 μm bonded to a PPS sheet with a thickness of 50 μm was used as the second cleaning member  39  with the setting of r=4 mm. p=3.7 mm, q=8 mm, θ=14° and biasing force by the torsion coil springs  45  being 0.2N, by which the creep deformation of the second cleaning member  39  could be prevented. 
       FIG. 11  shows the state that the cleaning device  30  which has finished cleaning starts to be separated from the intermediate transfer belt  24  by rotating around a rotation center  37 . Immediately after the first cleaning member  38  is separated from the intermediate transfer belt  24 , the second cleaning member  39  is still in pressure contact with the intermediate transfer belt  24  so that the separation streak left on the intermediate transfer belt  24  when the first cleaning member  38  is separated are removed by the second cleaning member  39 . 
     Upon separation of the cleaning device  30 , the second cleaning member  39  rotates with the rotation center  42  as a supporting point by biasing force by the torsion coil springs  45 . However, till the second cleaning member  39  reaches a rotation regulation position (i.e., a position at which the end section of the mounting member  43  comes into contact with the extension section  44   a  of the support member  44  as shown in  FIG. 9A ), the top end of the second cleaning member  39  keeps on being in pressure contact with the intermediate transfer belt  24 . Once the second cleaning member  39  has rotated to the rotation regulation position, the second cleaning member  39  is separated from the intermediate transfer belt  24  as the cleaning device  30  is separated therefrom. 
     Biasing force by the torsion coil springs  45 , which acts upon the rotation of the second cleaning member  39 , should be enough to offer smooth rotation. In order to supply the biasing force capable of offering smooth rotation while preventing deformation of the second cleaning member  39  in the state shown in  FIG. 8 , it is necessary to set the biasing force at a value close to a limit for preventing creep deformation and to decrease rotation resistance of the support member  44  onto which the second cleaning member  39  is fixed. 
     Toner and the like removed by the second cleaning member  39  in  FIG. 11  falls between the second cleaning member  39  and the first cleaning member  38  so as to be housed in the housing  41  and processed to prevent their spattering. In this operation, if it is concerned that the removed toner and the like are attached to the vicinity of the support shaft including the rotation center  42  to cause increased rotation resistance of the second cleaning member  39  or the toner and the like are fixed thereon to cause rotation failure, it is necessary to take a means to prevent attachment of the toner and the like thereto. 
     One example of the means is to displace the position of the rotation center  42  in direction vertical to the page of  FIG. 11  or to coat the area around the rotation center  42  with a cover. Moreover, performing pressure contact/separation operation of the cleaning device  30  at power-on or with specified timing (e.g., upon the elapse of specified time after completion of image formation, and upon recovery of the image forming apparatus  10  from a sleep mode) is an effective means to prevent fixation of the second cleaning member  39  onto the rotation center  42 . 
       FIG. 12  shows the state that the cleaning device  30  is completely separated from the intermediate transfer belt  24 . This state is similar to the initial state of the second cleaning member  39  in the conventional cleaning device  30 ′ shown in  FIG. 7A . The removed toner and the like are attached to the first cleaning member  38  and the second cleaning member  39 , and therefore the first cleaning member  38  and the second cleaning member  39  are put away from the intermediate transfer belt  24  by a specified distance so as to prevent the toner and the like from spattering. 
     Next, with reference to  FIG. 13 , description will be given of the relation among a moving velocity “V” of the intermediate transfer belt  24 , a time lag “t” between time when the first cleaning member  38  is away from the intermediate transfer belt  24  and time when the second cleaning member  39  is away from the intermediate transfer belt  24 , and a distance “L” between top ends of the first cleaning member  38  and the second cleaning member  39  on the intermediate transfer belt  24  when the top ends are away from the intermediate transfer belt  24 . 
       FIG. 13  shows the state shown in  FIG. 8  being shifted to the state shown in  FIG. 11 . Reference character “L A ” represents a position of the top end of the first cleaning member  38  on the intermediate transfer belt  24  at the point of time when the top end is away from the intermediate transfer belt  24 , reference character “L B ” represents a position of the top end of the second cleaning member  39  on the intermediate transfer belt  24  at the point of time when the top end is away from the intermediate transfer belt  24 . Since the intermediate transfer belt  24  moves at the velocity V, the position L A  of the first cleaning member  38  which moves away from the intermediate transfer belt  24  by a distance Vt during the elapse of time t reaches a position denoted by reference character “L A ′”. The reference character L represents a distance between L A  and L B . Consequently, during the elapse of the time lag t between time when the first cleaning member  38  is away from the intermediate transfer belt  24  and time when the second cleaning member  39  is away from the intermediate transfer belt  24 , the separation streak caused by the first cleaning member  38  moves by the distance Vt. 
     In order to remove the separation streak by the second cleaning member  39 , L&lt;Vt should be satisfied. In the case of L=Vt, in the instant when the separation streak reaches the top end position of the second cleaning member  39 , the second cleaning member  39  is away from the intermediate transfer belt  24 , and this makes it impossible to remove the separation streak. 
     In a contact section between the first cleaning member  38  and the intermediate transfer belt  24 , elastic deformation is generated depending on the respective materials and thicknesses. As a result, the separation streak generated at the time of separation of the first cleaning member  38  has a certain width. When a contact width of the first cleaning member  38  and the intermediate transfer belt  24  is assumed to be “b”, a width of the separation streak can be considered roughly as “b”. Moreover, with an allowance being “α” in consideration of a larger width of the separation streak or variations in components including the first cleaning member  38  and the second cleaning member  39 , a relation L+b+α≦Vt should be satisfied. Since the creep deformation of the second cleaning member  39  can be neglected in the present embodiment, it becomes possible to decrease the value α to a negligible level compared to the conventional cleaning device  30 ′. Therefore, the limitations of the range of the distance L is decreased and freedom in layout and shape of components of the cleaning device  30  is increased proportionally. 
     In one example in the present embodiment, setting of V=127 mm/sec, t=75 msec, b=3 mm, L=1.5 mm made it possible to secure satisfactory cleaning performance. 
     While the separation streak caused by the first cleaning member  38  has been described as a main removal target, if an electricity removal seal member is provided on the upstream side of the first cleaning member  38  and the first cleaning member  38  fails to remove the separation streak caused by the electricity removal seal member, then the separation streak should also be removed by the second cleaning member  39 . In the case where the removal target includes these residual toner streak and the like, it is necessary to attain the values L A , L B , L A ′, b and L depending on each target and to satisfy the above-stated relation. 
       FIG. 14  is a timing chart (for color print) for an image forming apparatus  10  having the cleaning device  30  in the present embodiment. Since the image formation process has already been described, the pressure contact/separation timing of the cleaning device  30  will be described in particular. Upon reception of a print start signal, a paper sheet is transported to a pair of the timing rollers  56  before the secondary transfer roller  28 . The image forming operation starts almost concurrently with the paper sheet transporting operation. In slight arrear of the start of primary-transfer for transferring a toner image from the photoreceptor  12  onto the intermediate transfer belt  24 , the cleaning device  30  is separated from the intermediate transfer belt  24 . The separation timing of the cleaning device  30  from the intermediate transfer belt  24  is determined such that residual toner by previous printing operation is removed and adverse effect is not exerted on a current printing target image. 
     While four toner images are superimposed in sequence on the intermediate transfer belt  24 , the cleaning device  30  is kept in a separated state. With timing of the start of the primary transfer of the fourth color toner image, a paper sheet transportation by a pair of the timing rollers  56  is started and secondary transfer by the secondary transfer roller  28  is started. In slight arrear of the secondary transfer, the cleaning device  30  is brought into pressure contact with the intermediate transfer belt  24 , and residual toner and the like are scraped and removed. When all the secondary transfer operations are finished and the paper sheet is discharged to the paper discharge section  60 , a series of print operations are completed. In the case of monochrome printing, the cleaning device  30  is constantly kept in pressure contact with the intermediate transfer belt  24 . That is because the secondary transfer is performed immediately after the primary transfer. 
       FIG. 15  is a schematic block diagram showing the image forming apparatus  10  having the cleaning device  30  in the present embodiment. Upon reception of a print start signal from a personal computer and the like, a CPU  11  constituting a control section drives a paper feed/transportation motor  13  to transport a paper sheet, and transmits a signal to a drive motor  15  to drive the photoreceptor  12  and the intermediate transfer belt  24 . Moreover, the pressure contact/separation operation of the cleaning device  30  is controlled by a pressure contact/separation motor  17 . While stepping motors are generally used as these motors and open loop control by pulse control is often employed, the states of respective driven members may be detected by unshown sensors where necessary. Moreover, the state of the image forming apparatus  10  is displayed on a display panel  19  constituting the display section. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the spirit and the scope of the present invention, they should be construed as being included therein.