Patent Abstract:
A belt unit of an electrophotographic printing apparatus, includes: two rollers for supporting a belt so as to be substantially in parallel with each other; two frames for supporting the rollers and attached to opposite ends of one of the rollers respectively so as to be perpendicular to the rollers; two support members attached to opposite ends of the other roller so as to be perpendicular to the rollers; two elastic members interposed between the two support members and the two frames respectively; and a belt mounting guide provided between the two frames. The belt mounting guide includes a rotating shaft disposed in parallel with the rollers, and an edge portion inclined relative to an axial direction of the rotating shaft.

Full Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a belt unit of an electrophotographic printing apparatus.  
           [0003]    2. Background Art  
           [0004]    Here will be described a belt unit, especially a belt photoconductor unit in an electrophotographic printing apparatus according to the related art.  
           [0005]    As a general configuration of a belt photoconductor unit, there is known a configuration in which a drive roller for rotating a belt photoconductor and a tension roller having tension urged by springs or the like are provided between two frames for supporting the rollers and in which the belt photoconductor is wound around the rollers.  
           [0006]    The belt photoconductor unit is configured so that a sensor for detecting a widthwise end of the belt photoconductor is provided on one of the frames or the like in order to perform detection of misalignment during rotation, detection of a seam of the belt photoconductor, and so on.  
           [0007]    The belt photoconductor needs to be exchanged for a new one periodically since it is an expendable article. At the time of exchange, it is necessary to remove the belt photoconductor from the frames and mount a new one. In the related art, it was necessary to shift the tension roller in a direction of narrowing the distance between the drive roller and the tension roller before removal/mounting of the belt photoconductor.  
           [0008]    Further, at the time of mounting of the belt photoconductor, the belt photoconductor must be mounted so as to be positioned in a groove of the sensor properly. This work was very difficult. As a related-art technique for setting the belt photoconductor in a proper position, there is known a technique in which: a first cam and a second cam for moving the tension roller in a direction of relaxing the belt photoconductor are provided on opposite ends of a rotating shaft; the length of the first cam is set to be larger than the length of the second cam; slowly increasing tension is applied to the belt photoconductor to thereby mount the belt photoconductor in the groove of the hole sensor (e.g., see JP-A-5-019667 (page 3 and FIG. 3)).  
           [0009]    According to the related art, it was structurally difficult to make the length difference between the first and second cams extremely large. For this reason, when a belt photoconductor having a large circumferential length was used, there was the possibility that the belt photoconductor would be scratched so as to be disabled from being used because slackness of the belt photoconductor could not be eliminated reliably to make it impossible to mount the belt photoconductor in the groove of the sensor accurately.  
           [0010]    Furthermore, the mounting position of the belt photoconductor was indefinite in the widthwise direction. For this reason, there was the possibility that the belt photoconductor could not exhibit its original performance because the belt photoconductor might be mounted in a position different from the original position where the belt photoconductor should be used. In addition, there was the possibility that the belt photoconductor would be damaged so as to be disabled from being used because the belt photoconductor might come into contact with the sensor.  
           [0011]    There was possibility that the belt photoconductor might be inserted into the electrophotographic printing apparatus body while the cams were not restored to their positions at the time of actual printing, that is, to the positions where tension would be applied to the belt photoconductor after the belt photoconductor was mounted. For this reason, there was the possibility that the belt photoconductor was scratched so as to be disabled from being used.  
         SUMMARY OF THE INVENTION  
         [0012]    It is an object of the invention to provide a belt photoconductor unit with a simple configuration that allows a belt to be mounted in a position where a sensor can detect the belt properly without damaging the belt.  
           [0013]    To achieve the object, the invention provides a belt unit of an electrophotographic printing apparatus, including: two rollers for supporting a belt so as to be substantially in parallel with each other; two frames for supporting the rollers and attached to opposite ends of one of the rollers respectively so as to be perpendicular to the rollers; two support members attached to opposite ends of the other roller so as to be perpendicular to the rollers; two elastic members interposed between the two support members and the two frames respectively; and a belt mounting guide provided between the two frames; wherein the belt mounting guide includes a rotating shaft disposed in parallel with the rollers, and an edge portion inclined relative to an axial direction of the rotating shaft.  
           [0014]    Preferably, a step portion is provided at one end of the edge portion of the belt mounting guide and in a position where the belt travels normally.  
           [0015]    Preferably, when the belt is mounted, the belt mounting guide is located to be higher than a frame that forms a slot portion included in an apparatus body in which the belt unit is mounted.  
           [0016]    Preferably, the rotating shaft of the belt mounting guide is provided with a blade for cleaning a back surface of the belt.  
           [0017]    The invention provides an electrophotographic printing apparatus, including: an apparatus body; and a belt unit installed in the apparatus body; wherein the belt unit includes: a belt, two rollers for supporting the belt so as to be substantially in parallel with each other, two frames for supporting the rollers and attached to opposite ends of one of the rollers respectively so as to be perpendicular to the rollers, two support members attached to opposite ends of the other roller so as to be perpendicular to the rollers, two elastic members interposed between the two support members and the two frames respectively, and a belt mounting guide provided between the two frames; and the belt mounting guide includes a rotating shaft disposed in parallel with the rollers, and an edge portion inclined relative to an axial direction of the rotating shaft.  
           [0018]    Preferably, the apparatus body includes a frame that forms a slot portion in which the belt unit is installed; and, when the belt is mounted, the belt mounting guide is located to be higher than the frame. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The present invention may be more readily described with reference to the accompanying drawings:  
         [0020]    [0020]FIG. 1 is a schematic view of a belt mounting mechanism according to the invention.  
         [0021]    [0021]FIG. 2 is a schematic view of the belt mounting mechanism according to the invention at the time of traveling of a belt after mounting of the belt.  
         [0022]    [0022]FIG. 3 is a schematic configuration diagram of an electrophotographic printing apparatus to which the invention is applied. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    An embodiment of the invention will be described below. Although this embodiment will be described on the case in which a belt photoconductor is used, the invention is not limited to the belt photoconductor but may be applied to an intermediate transfer belt, a transfer belt, a fixing belt, etc.  
         [0024]    [0024]FIG. 1 is a schematic view of a belt photoconductor unit  110  according to an embodiment of the invention at a point of time when a belt photoconductor used in the belt photoconductor unit  110  is mounted in an electrophotographic printing apparatus.  
         [0025]    The belt photoconductor unit  110  according to the embodiment of the invention includes: a belt photoconductor  1  which is a detachably mountable photoconductor shaped like a belt; frames  2   a  and  2   b ; a drive roller  3  for driving the belt photoconductor  1  to rotate; a tension roller  4  for adjusting tension acting on the belt photoconductor  1 ; and support members  5  for connecting the tension roller  4  to the frames  2   a  and  2   b . The belt photoconductor unit  110  further includes: a first rotating shaft  6  disposed between the frames  2   a  and  2   b ; cams  7  and a first lever  8  connected to opposite ends of the first rotating shaft  6 ; springs  9  for applying tension to the tension roller  4  in a direction of moving away from the driver roller  3 ; and guide shafts  10  for guiding the respective springs  9 .  
         [0026]    While one of the support members  5 , one of the cams  7 , one of the springs  9  and one of the guide shafts  10  are attached to the frame  2   a , the other support member  5 , the other cam  7 , the other spring  9  and the other guide shaft  10  are attached to the frame  2   b  in the same manner. The tension roller  4  is therefore supported by the support members  5 , the cams  7 , the springs  9  and the guide shafts  10 .  
         [0027]    When the first lever  8  is rotated, the cams  7  can be also rotated to move the tension roller  4  and the support members  5  in a direction of tensing or relaxing the belt photoconductor  1  (an axial direction of each guide shaft  10 ). Each cam  7  used herein is an eccentric cam.  
         [0028]    The guide  12  is formed so that its height varies in the widthwise direction of the belt photoconductor  1 , that is, the height of the guide  12  increases slowly as the belt photoconductor  1  is mounted more deeply. When second lever  13  is rotated, the guide  12  is also rotated so as to go out or come in.  
         [0029]    For example, the sensor  14  is a transmission type sensor which detects meandering of the belt photoconductor  1  when printing is actually performed. The sensor  14  is disposed so that one widthwise end portion of the belt photoconductor  1  faces a U-shaped groove of the sensor  14 . Although the description of how to correct meandering will be omitted here, for example, the method described in JP-A-2002-296972 may be used, which is incorporated by reference. In this embodiment, as shown in FIG. 1, the sensor is attached to a position opposite to an end of the lower part of the belt when the belt photoconductor is mounted.  
         [0030]    The operation of mounting the belt photoconductor will be described below with reference to FIG. 1.  
         [0031]    When the belt photoconductor  1  is mounted, the belt photoconductor  1  is horizontally pulled out from the electrophotographic printing apparatus body not shown, and the first lever  8  is rotated in the direction of relaxing the tension roller  4  as shown in FIG. 1 to thereby mount the belt photoconductor  1 . At the same time, the second lever  13  is also rotated to locate the guide  12  in the position shown in FIG. 1.  
         [0032]    The guide  12  has a rotating shaft, and an edge portion inclined relative to the shaft.  
         [0033]    Because of the shape of the guide  12 , the height of the guide  12  increases slowly in the direction of tensing the belt photoconductor  1  as the belt photoconductor  1  is mounted more deeply. As a result, slackness of the lower part of the belt photoconductor  1  is eliminated, so that the belt photoconductor  1  is mounted in the groove of the sensor  14  firmly.  
         [0034]    A step portion  12   a  (see FIG. 2) is provided at an end of the guide  12 . The end of the belt photoconductor  1  abuts on the step portion  12   a  at the end of the guide  12  as the belt photoconductor  1  is mounted deeply. As a result, the belt photoconductor  1  is aligned with a line along which the belt photoconductor  1  will travel at the time of actual printing.  
         [0035]    At the time of mounting of the belt photoconductor, the guide  12  needs to be located in a position (see FIG. 1) protruded upward of the frames  2   a  and  2   b  from its normal position used at the time of actual printing. Therefore, at the time of mounting of the belt photoconductor, the guide  12  is configured so as be higher than a frame  24  that forms each slot portion of the apparatus body  100  (See FIG. 3). In this manner, the guide  12  has a miss-insertion preventing function which prevents the belt from being inserted into the electrophotographic printing apparatus body by mistake in the condition that the belt has not completely mounted yet.  
         [0036]    [0036]FIG. 2 shows a schematic view of the belt photoconductor unit  110  at the time of actual printing.  
         [0037]    In FIG. 2, at the time of actual printing, the first lever  8  is rotated to make the tension roller  4  tense the belt photoconductor  1  whereas the second lever  13  is rotated to the position shown in FIG. 2 to prevent the guide  12  from coming into contact with the belt photoconductor  1 .  
         [0038]    On this occasion, a blade  15  attached to the second rotating shaft  11  is located in a position where the blade  15  comes into contact with a back surface of the belt photoconductor  1 . As a result, the blade  15  cleans the back surface of the belt photoconductor  1 . The back surface of the belt photoconductor  1  is smeared, for example, with toner scattered at the time of actual printing but can be cleaned by the blade  15 .  
         [0039]    An overall configuration of an electrophotographic printing apparatus using belt photoconductors as shown in FIG. 1 will be described below with reference to FIG. 3.  
         [0040]    An imaging unit  16   a  includes a belt photoconductor  17   a , a charger  18   a , an exposure device  19   a , a development device  20   a , a transfer device  21   a , and a cleaning device  22   a . Each of imaging units  16   b ,  16   c , and  16   d  has the same configuration as that of the imaging unit  16   a.    
         [0041]    The imaging units  16   a ,  16   b ,  16   c , and  16   d  are used for printing different colors on a sheet of paper  23 . For example, the imaging unit  16   a  is used for printing yellow, the imaging unit  16   b  for printing magenta, the imaging unit  16   c  for printing cyan, and the imaging unit  16   d  for printing black.  
         [0042]    The printing operation of the imaging unit  16   a  will be described below.  
         [0043]    The belt photoconductor  17   a  starts rotating on the basis of a printing operation start signal given from a controller not shown. The belt photoconductor  17   a  rotates at a speed equivalent to the printing speed of the electrophotographic printing apparatus so that the rotation of the belt photoconductor  17   a  continues until the printing operation is completed. When the belt photoconductor  17   a  starts rotating, a high voltage is applied to the charger  18   a  so that a surface of the belt photoconductor  17   a  is evenly charged, for example, with positive charges.  
         [0044]    When character/graphic data converted into dot images are transmitted from the controller not shown to the electrophotographic printing apparatus so that the dot images serve as on/off signals for the exposure device  19   a , regions irradiated with laser light emitted from the exposure device  19   a  and regions not irradiated with the laser light are formed in the surface of the belt photoconductor  17   a . Whenever a portion of the belt photoconductor  17   a  which have been destaticized by the irradiation with the laser light emitted from the exposure device  19   a  reach a position facing the development device  20   a , this portion of the belt photoconductor  17   a  attracts positively charged toner by static electricity. In this manner, atoner image is formed on the belt photoconductor  17   a . The sheet of paper  23  is transported in synchronism with the timing at which the print data formed on the belt photoconductor  17   a  reach a transfer position. The toner image formed on the belt photoconductor  17   a  is attracted onto the sheet of paper  23  by the transfer device  21   a &#39;s function of charging the back surface of the sheet of paper  23  with charges reverse in polarity to the toner image. Incidentally, after passing through the transfer position, the belt photoconductor  17   a  is cleaned by the cleaning device  22   a  and any residual toner on the belt photoconductor  17   a  is sucked in by a suction blower not shown and collected into a collecting portion not shown, in order to be ready for the next printing operation.  
         [0045]    After passing through the imaging unit  16   a , the sheet of paper  23  is subjected to similar printing operations at the imaging units  16   b ,  16   c , and  16   d  successively and then transported to a fixing device not shown. The toner image on the sheet of paper  23  that has arrived at the fixing device is melted and fixed on the sheet of paper  23 .  
         [0046]    Each of the belt photoconductors  17   a ,  17   b ,  17   c  and  17   d  needs to be exchanged for a new one periodically, since the belt photoconductors  17   a ,  17   b ,  17   c  and  17   d  deteriorate while printing operations are repeated.  
         [0047]    The use of the belt mounting mechanism in the invention makes it possible to reduce slackness of the belt more reliably than in the related art. Accordingly, an operator can mount the belt in the sensor easily. As a result, it is possible to prevent the belt photoconductor from being damaged and disabled before start of a printing operation.  
         [0048]    In addition, the belt mounting guide shares the same rotating shaft with the blade for cleaning the back surface of the belt. Accordingly, the blade can be installed reliably to ensure the cleaning of the belt photoconductor during actual printing.  
         [0049]    As described above, the invention makes it possible to mount a belt in a sensor easily without damaging the belt in spite of a simple configuration. In addition, a blade can be mounted reliably to allow a back surface of the belt to be cleaned during actual printing.

Technology Classification (CPC): 6