Patent Publication Number: US-7583921-B2

Title: Image forming apparatus and transfer unit

Description:
BACKGROUND 
   1. Technical Field 
   The present invention relates to electrophotographic image forming apparatuses that perform either copier, printer or facsimile machine functions, or to multifunctional apparatuses that perform all of these functions, and to transfer units that are employed for these image forming apparatuses. 
   2. Related Art 
   In an electrophotographic image forming apparatus such as a copier or a printer, for example, a developing device (a developing unit) employs a developer to form an electrostatic latent image on a photosensitive drum, and then, the toner image produced on the photosensitive drum is transferred and fixed to a recording medium, conveyed by a sheet feeding unit, to obtain a printed image. Some image forming apparatuses of this type include a belt conveying device, such as an endless intermediate transfer belt, a photosensitive belt or a sheet conveying belt. More specifically, intermediate transfer belts are provided for certain color image forming apparatuses, of a tandem type, that include image forming units for the individual colors yellow, magenta, cyan and black. 
   Generally, for a belt drive unit for which, to support an endless belt, there are provided a predetermined number of rollers, certain of which are employed to drive the endless belt, the endless belt, while being driven, is shifted width wise (perpendicular to the direction in which the belt is being driven), i.e., a so-called belt walk phenomenon (belt skewing) occurs. This belt walk phenomenon causes the positions of individual color images to be shifted when the tandem color image forming apparatus transfers and superimposes these images on the intermediate transfer belt. That is, belt walk causes misregistration and the uneven application of image colors. Therefore, in order to produce a high quality image, belt walk must be prevented. 
   SUMMARY 
   According to an aspect of the invention, there is provided an image forming apparatus for forming an image on a recording medium, which comprises: 
   a belt-like member that is capable of cyclic rotation; 
   a plurality of support members, along which the belt-like member is stretched; 
   a first member that is located along an inner face of the belt-like member; and 
   a regulator that is located opposite the inner face of the belt-like member, wherein the regulator maintains a cyclic rotating state for the belt-like member while ensuring the first member is separated by a gap from the belt-like member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
       FIG. 1  is a schematic diagram showing the configuration of an image forming apparatus according to an aspect of the present invention; 
       FIG. 2  is a diagram for explaining the operation of a manual feeding tray; 
       FIG. 3  is a diagram for explaining the employment of a front cover; 
       FIG. 4  is a diagram for explaining the state of a sheet cassette when pulled forward; 
       FIG. 5  is a diagram for explaining a transfer unit according to a first exemplary embodiment of the present invention; 
       FIG. 6  is a diagram showing the transfer unit viewed from the direction indicated by an arrow VI in  FIG. 5 ; 
       FIG. 7  is a diagram for explaining a transfer unit according to a second exemplary embodiment of the present invention; and 
       FIG. 8  is a diagram showing the transfer unit viewed from the direction indicated by an arrow VIII in  FIG. 7 . 
   

   DETAILED DESCRIPTION 
   The preferred embodiments of the present invention will now be described in detail while referring to the accompanying drawings. 
     FIG. 1  is a schematic diagram showing the configuration of an image forming apparatus according to an aspect of the invention. 
   An image forming apparatus  10  in  FIG. 1  is a so-called tandem type, wherein processing cartridges (image forming units or drum cartridges) for four colors  11   a ,  11   b ,  11   c  and  11   d  are sequentially arranged, vertically, within a main body  10   a . A conveying path  12 , along which a sheet (a recording medium) P is to be conveyed substantially perpendicularly upward, from below, is appropriately arranged relative to the processing cartridges  11   a  to  11   d . A sheet cassette  13  is located below (upstream of) the lowermost (furthest upstream) processing cartridge  11   a , for storing sheets P, each of which is to be conveyed along the conveying path  12 , to which toner images are sequentially to be transferred. In accordance with the size of the sheets P stacked in the sheet cassette  13 , part of the sheet cassette  13  is projected outward, to the back of the main body  10   a  (the rear side or the rear wall side). When the sheets P are small, the sheet cassette  13  does not project outward from the main body  10   a.    
   The processing cartridges  11   a  to  11   d  form yellow (Y), magenta (M), cyan (C) and black (K) toner images, beginning upstream, along the conveying path  12 . The individual processing cartridges  11   a  to  11   d  are cartridges produced by packaging photosensitive drums (image bearing members)  14  and various types of electrophotographic devices that are arranged around the photosensitive drums  14 . These electrophotographic devices are: charge rollers, for the prior electrification of the photosensitive drums  14 ; developing devices, for employing corresponding toners to develop electrostatic latent images, formed through the exposure of the photosensitive drums  14  that have been electrified by the charge rollers; and cleaning devices, for removing waste toner from the photosensitive drums  14 . 
   An exposure device (ROS)  15 , used in common by the processing cartridges  11   a  to  11   d , is located on the opposite side, along the conveying path  12  for the processing cartridges  11   a  to  11   d . The exposure device  15  controls four semiconductor lasers (not shown), based on image data consonant with the individual colors. Beams emitted by the four semiconductor lasers, which are to be used for scanning, are deflected by polygon mirrors (not shown), and these beams are guided through fθ lenses, and by a plurality of reflecting mirrors (none of them shown), to exposure points on the photosensitive drums  14 , whereon they form optical images. 
   A conveying belt (a belt-like member or a transfer belt)  16 , which cyclically rotates along the conveying path  12 , is arranged at a location corresponding to the photosensitive drums  14  of the processing cartridges  11   a  to  11   d . The conveying belt  16  is composed of a material that can electrostatically attract a sheet P, and is extended between a paired driven roller (a support member)  17 A and a drive roller (a support member)  17 B. Further, an attraction roller  18 , for electrostatically attracting a sheet P to the conveying belt  16 , is provided along the conveying path  12 . 
   Transfer rollers  19  are arranged, along the reverse face of the conveying belt  16 , at locations corresponding to the photosensitive drums  14  of the processing cartridges  11   a  to  11   d . The transfer rollers  19  are used to facilitate the transfer of toner images from the photosensitive drums  14  to a sheet P, while the sheet P is held on the transfer belt  16  so as to closely contact the photosensitive drums  14 . 
   A fixing device  20  is arranged along the conveying path  12  above (downstream of) the topmost (furthest downstream) processing cartridge  11   d . In the upper portion of the main body  10   a , a discharge unit  21  is integrally formed with the main body  10   a  for storing sheets P to which toner images have been fixed by the fixing device  20  and which are discharged thereafter. Further, in the main body  10   a , an inversion conveying path  22  is arranged to invert the sides of the sheet P to which an image has been fixed by the fixing device  20 , and to again feed the sheet P to the conveying path  12 . 
     FIG. 2  is a diagram for explaining a manual feeding tray  23 . 
   As shown in  FIG. 2 , the manual feeding tray  23  is provided for the main body  10   a  of the image forming apparatus  10 , and can pivot at a fulcrum J provided at the lower end. That is, the manual feeding tray  23  can be opened or closed to the near side (to the front, or to the outer side). When the manual feeding tray  23  is pivoted to open, desired sheets P can be inserted into an insertion slot (not shown). As described above, the image forming apparatus  10  is designed so that sheets P, other than those sheets P stacked in the sheet cassette  13 , can be supplied via the manual feeding tray  23 . 
   When sheets P to which toner images are to be transferred are set up and a user issues an instruction to a controller (not shown), either a sheet P in the sheet cassette  13  or a sheet P in the manual feeding tray  23  is fed at a predetermined timing. The sheet P is then guided to the conveying path  12  via a plurality of conveying rollers  24 , and is conveyed along the conveying belt  16  to the transfer positions for the individual processing cartridges  11   a  to  11   d.    
     FIG. 3  is a diagram for explaining a front cover  25 . 
   As shown in  FIG. 3 , a front cover  25  provided for the main body  10   a  of the image forming apparatus  10  pivots at a fulcrum J located at its lower end. In the closed state, the front cover  25 , along with the main body  10   a , serves as an outer cover. That is, the front cover  25  serves as the front side wall of the image forming apparatus  10  above the sheet cassette  13 . 
   The conveying belt  16 , the driven roller  17 A, the drive roller  17 B, the attraction roller  18 , the transfer rollers  19  and the inversion conveying path  22  are mounted in the front cover  25 . Therefore, when the front cover  25  is opened, accordingly, these parts are separated from the main body  10   a . Thus, when the front cover  25  is opened, the processing cartridges  11   a  to  11   d  are exposed and a user can easily access the conveying path  12 . 
   The individual processing cartridges  11   a  to  11   d  are mounted so that they are almost horizontally detachable from the main body  10   a . Therefore, when the front cover  25  of the main body  10   a  has been opened, the processing cartridges  11   a  to  11   d  can be detached. It should be noted that a set detection sensor (not shown) detects the setting states of the processing cartridges  11   a  to  11   d , and outputs the detection results to the controller (not shown). 
   As described above, by opening the front cover  25 , the processing cartridges  11   a  to  11   d  can be exposed and exchanged. Further, since the photosensitive drums  14  are also exposed, paper jamming can be coped with (jams can be cleared). In this manner, maintenance of the image forming apparatus  10  is improved. 
     FIG. 4  is a diagram for explaining the state wherein the sheet cassette  13  is pulled to the front. 
   The sheet cassette  13  is stored in a cassette accommodating portion  26  in the main body  10   a , and is to be extracted from the front of the main body  10   a . More specifically, while the manual feeding tray  23  and the front cover  25  are closed, the sheet cassette  13  can be extracted from or inserted into the cassette accommodating portion  26 . 
   An insertion slot is formed in the sheet cassette  13  to set up sheets P for the manual feeding tray  23 . Furthermore, some of the conveying rollers  24 , for conveying the sheets P from the manual feeding tray  23 , are provided for the sheet cassette  13 . As described above, a feeding path, along which a sheet P set up at the insertion slot is guided to the conveying path  12 , is formed in the sheet cassette  13 . 
   FIRST EXEMPLARY EMBODIMENT 
     FIG. 5  is a diagram for explaining a transfer unit  30  according to a first exemplary embodiment of the present invention. The transfer unit  30  is a unit obtained by integrally forming the conveying belt  16 , the driven roller  17 A, which is positioned low, so as to support the conveying belt  16 , the drive roller  17 B, which is positioned high, so as to support the conveying belt  16 , and which is a driver for driving the conveying belt  16 , the attraction roller  18  (see  FIGS. 1 to 4 ) and the transfer rollers  19 . The transfer unit  30  is to be exchanged during checkup servicing or maintenance, and should be handled separately from the image forming apparatus  10 . In  FIG. 5 , the attraction roller  18  is not shown. 
   As shown in  FIG. 5 , the transfer unit  30  includes a box (member)  31  of the transfer unit  30  that is located inside the conveying belt  16 . The box member  31  is positioned between the driven roller  17 A and the drive roller  17 B that support the conveying belt  16 . The box member  31  is made of metal and is sufficiently rigid to hold the four transfer rollers  19  and to permit them to rotate. 
   The transfer unit  30  also includes a regulating member (a regulator)  32 . That is, a cleaner  27  for cleaning the conveying belt  16  is arranged downstream of the drive roller  17 B, and the regulating member (the regulator)  32  is located on the box member  31 , downstream, immediately behind the cleaner  27 . 
   The regulating member  32  is located on the face of the box member  31 , opposite the transfer roller  19  and facing the inner wall of the conveying belt  16 , and maintains the gap between the conveying belt  16  and the box member  31 . That is, the regulating member  32  is arranged so it faces the inner wall of the conveying belt  16  and maintains the conveying belt  16  so that it does not contact the box member  31 . 
   A device composed of a comparatively soft material, such as a sponge or a brush, is used for the regulating member  32 , so that when the regulating member  32  contacts the inner wall of the conveying belt  16 , it will neither damage the conveying belt  16  nor reduce its service life. That is, the regulating member  32  is made of a material that is more easily abraded and has a smaller friction coefficient than has the material used for the conveying belt  16 . 
   The cleaner  27  impels the conveying belt  16  toward the box member  31  to ensure the performance of an adequate cleaning function. Thus, the clearance between the conveying belt  16  and the box member  31  is minimal near the cleaner  27 , so that the conveying belt  16  may contact the box member  31 . Further, the probability such a contact will occur is high because the side downstream of the drive roller  17 B is the slack side, not the taut side. Therefore, in this exemplary embodiment, the regulating member  32  is provided on the box member  31  where the clearance relative to the conveying belt  16  is reduced. As a result, when the conveying belt  16  fluctuates during cyclic rotation, the regulating member  32  can restrain the conveying belt  16 . And thus, since the regulating member  32  is so arranged, excessive friction exerted against the box member  31  can be prevented and the appearance on the conveying belt  16  of belt stripes (areas of surface roughness), which would adversely affect the appearance of an image, can be avoided. 
   In this exemplary embodiment, the regulating member  32  is located at a corner of the box member  31 . However, the regulating member  32  may be arranged at another location whereat the clearance, relative to the conveying belt  16  is minimal, or at a location whereat the conveying belt  16  is the slackest. 
     FIG. 6  is a diagram showing the transfer unit  30  as viewed from the direction indicated by an arrow VI in  FIG. 5 . For convenience sake, and to simplify the explanation, the cleaner  27  is not shown in  FIG. 6 . 
   As shown in  FIG. 6 , the regulating member  32  is attached to the box member  31  so that it is positioned outside the image area on the conveying belt  16 . In other words, the regulating member  32  is attached to the box member  31  outside the portion corresponding to the image area on the conveying belt  16 . Therefore, should a belt stripe appear on the conveying belt  16  due to contact with the regulating member  32 , the location of the belt stripe will be outside the image area on the conveying belt  16 . Thus, the occurrence of stripes in the image area on the conveying belt  16  can be prevented, and the affect such stripes may have on an image can be avoided. 
   SECOND EXEMPLARY EMBODIMENT 
     FIG. 7  is a diagram for explaining a transfer unit  30  according to a second exemplary embodiment of the present invention. The basic arrangement for the transfer unit  30  in  FIG. 7  is the same as that for the transfer unit of the first exemplary embodiment, and only the portion that is different will now be described. Further, the same reference numerals as are used for the first exemplary embodiment are also employed to denote identical or corresponding components, and for these components, no further explanation will be given. 
   As shown in  FIG. 7 , the transfer unit  30  includes a regulating roller (a rotary member)  33  that is rotatably supported by a box member  31 . The regulating roller  33  is employed instead of the regulating member  32  in the first exemplary embodiment in order to prevent a conveying belt  16  from contacting the box member  31 . The regulating roller  33  is so arranged that an outer surface  33   a  (a regulating portion) can contact the inner surface of the conveying belt  16 . More specifically, the regulating roller  33  does not always contact the conveying belt  16 , but instead, contacts it only when the conveying belt  16  fluctuates, and is thus able to regulate the movement of the conveying belt  16 . If the regulating roller  33  were constantly in contact with the conveying belt  16 , the tension provided for the conveying belt  16  would be affected, and an adjustment for belt walk would be required. Therefore, in this exemplary embodiment, the conveying belt  16  is employed to control the wobbling of the regulating roller  33 . 
   Furthermore, when a three-axis arrangement is employed, by providing a support roller in addition to a driven roller  17 A and a drive roller  17 B, that arrangement is effective because a larger space, defined by the conveying belt  16 , can be obtained. However, in this case, belt walk could occur, depending on the accuracy with which the support roller is positioned, and thus, precise management of the position of the support roller is required. In the event, rollers that prevent the fluctuation of the conveying belt  16  must merely be arranged so that they do not always contact each other, so that a space that is less affected by belt walk can be obtained inside the conveying belt  16 . 
     FIG. 8  is a diagram showing the transfer unit  30  when viewed in the direction indicated by an arrow VIII in  FIG. 7 . 
   As shown in  FIG. 8 , the regulating roller  33  is attached to the box member  31  so that it is positioned inside the image area on the conveying belt  16 . Since the regulating roller  33  is rotated by contact with the inner surface of the conveying belt  16 , the degree to which the regulating roller  33  can damage the conveying belt  16  is less than the damage that can be inflicted by the regulating member  32  of the first exemplary embodiment. Therefore, when the regulating roller  33  is attached to the portion of the box member  31  corresponding to the image area, adverse image effects can be avoided, or reduced. 
   The foregoing description of the exemplary embodiments of the present invention has been provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments are chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various exemplary embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.