Abstract:
A fixing apparatus for fixing an image formed on a recording material, the fixing device includes a guiding member for guiding movement of the recording material, provided in a recording material passing opening of the apparatus; a rib projecting from a recording material passing surface of the guiding member, for being contacted by the recording material; a shutter provided at a position opposing the guiding member and movable between a position for opening the passing opening and a position closing the passing opening, and a projection provided at a position of the shutter opposing a position of the guiding member not having the rib with respect to a direction perpendicular to a recording material feeding direction, wherein when the shutter takes the closing position, a clearance between the rib and the shutter is larger than a clearance between the guiding member and the projection.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a fixing apparatus which is employable by an electrophotographic image forming apparatus. 
         [0002]    Some conventional image forming apparatuses which are equipped with a fixing apparatus are provided with a shutter for keeping closed the openings of the recording medium conveyance passage of the fixing apparatus, in order to prevent a user from touching the interior of the fixing apparatus when the user installs a process cartridge into the main assembly of the image forming apparatus, or removes a process cartridge from the main assembly, and also, when the user deals with a paper jam or the like problems. For example, in the case of the image forming apparatus disclosed in Japanese Laid-open Patent Application 2002-323822, the main assembly of the image forming apparatus is provided with a door for allowing a user (operator) to access the interior of the image forming apparatus, and its fixing apparatus is provided with a shutter which is rotationally moved by the opening and closing movement of the door of the main assembly. During an image forming operation, the shutter is kept in a position in which it keeps open the recording medium passage of the fixing apparatus, whereas during a period in which the door of the main assembly of the image forming apparatus is open, for example, during a period in which the user deals with a paper jam or the like, the shutter is kept in a position in which it keeps shut the recording medium conveyance passage of the fixing apparatus, in order to prevent the user from touching the fixation film and pressure roller in the fixing apparatus while the user is dealing with the a paper jam or the like. 
         [0003]    More specifically, as the shutter is moved into its closed position, its comes into contact with stoppers which are outside the recording medium passage, in terms of the direction perpendicular to the recording medium conveyance direction, being thereby properly positioned to keep closed the recording medium conveyance passage of the fixing apparatus. Further, the fixing apparatus is structured so that when the shutter is in its closed position, there is a space between the portion of the shutter, which corresponds in position to the recording medium conveyance passage of the fixing apparatus, and the recording medium conveyance guide of the fixing apparatus; the portion of the shutter, which corresponds in position to the recording medium conveyance passage of the fixing apparatus, is prevented from coming into contact with the recording medium conveyance guide. However, the shutter is sometimes bent or warped by external force when it is closed or in its closed position. Further, the shutter itself may naturally bend or warp, or may be made to bend or warp by the components related to the shutter. In the case of the conventional fixing apparatus provided with the above-described shutter, therefore, the recording medium guiding surface (which comes into contact with recording medium) of the recording medium conveyance guide is sometimes damaged. If the portions of the recording medium guide of the fixing apparatus, which come into contact with recording medium, is damaged, the fixing apparatus is likely to reduce in the accuracy with which it can convey recording medium. For example, it is likely to suffer from a paper jam or the like problems. Obviously, these problems can be prevented by such measures as increasing the shutter and the components related to the shutter in dimensional accuracy, and/or increasing the shutter and the components related to the shutter in rigidity, in order to prevent the shutter from bending or warping. These methods, however, invite increase in fixing apparatus cost and image forming apparatus cost. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention was made in consideration of the problems described above. Thus, the primary object of the present invention is to provide a fixing apparatus the shutter of which does not damage the recording medium guiding surface of the recording medium guide of the fixing apparatus, which faces the shutter, when the shutter is closed or in its closed position, and yet, which is no higher in cost than any of conventional fixing apparatuses. 
         [0005]    According to an aspect of the present invention, there is provided a fixing apparatus for fixing an image formed on a recording material, said fixing device comprising a guiding member for guiding movement of the recording material, provided in a recording material passing opening of said apparatus; a rib projecting from a recording material passing surface of said guiding member, for being contacted by the recording material; a shutter provided at a position opposing said guiding member and movable between a position for opening the passing opening and a position closing the passing opening, and a projection provided at a position of said shutter opposing a position of said guiding member not having said rib with respect to a direction perpendicular to a recording material feeding direction, wherein when said shutter takes the closing position, a clearance between said rib and said shutter is larger than a clearance between said guiding member and said projection. 
         [0006]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic sectional view of a laser beam printer, that is, an example of an image forming apparatus, and shows the general structure of the printer. 
           [0008]      FIG. 2  is an enlarged sectional view of the fixing apparatus  18 . 
           [0009]      FIG. 3  is a plan view of the entrance guide of the fixing apparatus, as seen from the direction indicated by an arrow mark in  FIG. 2 . 
           [0010]      FIG. 4  is a perspective view of the entrance guide and shutter of the fixing apparatus. 
           [0011]      FIG. 5  is a detailed perspective of the stopper portion of the fixing apparatus. 
           [0012]      FIG. 6  is a detailed plan view of the entrance guide and shutter of the fixing apparatus, as seen from the upstream side of the fixing apparatus in terms of the recording medium conveyance direction. 
           [0013]      FIG. 7  is a detailed sectional view of the entrance guide and shutter of the fixing apparatus, at a plane A-A in  FIG. 6 , and shows Clearance C 1  of the fixing apparatus. 
           [0014]      FIG. 8  is a detailed sectional view of the entrance guide and shutter of the fixing apparatus, at a plane B-B in  FIG. 6 , and shows Clearance C 2  of the fixing apparatus. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     General Structure of Image Forming Apparatus 
       [0015]    Hereinafter, the image forming apparatus in one of the preferred embodiment of the present invention is described, with the reference to the appended drawings. 
         [0016]      FIG. 8  is a schematic sectional view of the image forming apparatus equipped with a fixing apparatus in accordance with the present invention, and shows the general structure of the image forming apparatus. Referring to  FIG. 1 , the image forming apparatus  1  has a scanner unit  2 , that is, an optical means, which scans the peripheral surface of an image bearing member (photosensitive drum  1 ) with a beam of laser light which it projects while modulating the beam with signals which are in accordance with the information of an image to be formed. Designated by a referential code  10  is a process cartridge which contains an image forming means, which includes a photosensitive drum  3  (image bearing member), and a charging device  4  of the roller type (roller is made up of semiconductive rubber). The process cartridge  10  has also a developing apparatus  5  and a cleaner, which also are integral parts of the process cartridge  10 . The developing apparatus  5  develops an electrostatic latent image on the photosensitive drum  3 , by transferring toner  6  onto the peripheral surface of the photosensitive drum  3 . The cleaner removes the waste toner from the peripheral surface of the photosensitive drum  3 . 
         [0017]    As the photosensitive drum  3  in the process cartridge  10  is rotated, the peripheral surface of the photosensitive drum  3  is uniformly charged by the charging device  4  of the roller type. Then, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum  3  by the beam of laser light projected upon the peripheral surface of the photosensitive drum  3  by the scanner unit  2 . Then, the electrostatic latent image is developed by the developing apparatus  5 ; the latent image is supplied with toner by the developing apparatus  5 , whereby a visible image, which reflects the latent image, is formed of the toner, on the peripheral surface of the photosensitive drum  3 . 
         [0018]    There are multiple sheets  12  of recording medium in a sheet feeder cassette  11 . The sheets are stored in layers in the cassette  11 . The sheet  12  of recording medium is a sheet of paper, for example, and is roughly 64-216 g in basis weight. Each sheet  12  of recording medium in the cassette  11  is fed into the main assembly of the image forming apparatus by a feed roller  13 , while being separated one by one from the rest by a feed roller  13 . After being fed into the main assembly, each sheet  12  of recording medium is conveyed to a pair of registration rollers  15  while being guided by top and bottom guides. The registration rollers  15  remain stationary until the arrival of the sheet  12  of recording medium (until sheet  12  pressed upon registration roller  15 ). Thus, as the leading edge of the sheet  12  of recording medium comes into contact with the registration, the sheet  12  is made to correct itself in angle by the registration rollers  15 . 
         [0019]    Then, the registration rollers  15  conveys the sheet  12  of recording medium to the transfer portion in such a manner that the leading edge of the image bearing area of the sheet  12  arrives at the transfer portion of the image forming apparatus  1  at the same time as the leading edge of the toner image formed on the peripheral surface of the photosensitive drum  3  arrives at the transfer portion. Incidentally, the image forming apparatus  1  is provided with a sensor (unshown), which is in the adjacencies of the pair of registration rollers  15  and detects the state of conveyance of the sheet  12 , for example, recording medium jam (paper jam), and the length of the sheet  12 . 
         [0020]    After the sheet  12  of recording medium is conveyed to the transfer portion, it is conveyed through the transfer portion while electric charge, which is opposite in polarity from the toner, is applied to the back surface of the sheet  12  (opposite surface of sheet  12  from photosensitive drum  3 ) by a transfer roller  7 . Thus, the toner image on the photosensitive drum  3  is transferred onto the sheet  12  as the sheet  12  is conveyed through the transfer portion. After the transfer of the toner image onto the sheet  12  in the transfer portion, the sheet  12  is conveyed to a fixing apparatus  18  (fixing means) while being guided by a sheet guide  16 . The fixing apparatus  18  fixes the unfixed toner image on the sheet  12  by applying heat and pressure to the toner image and sheet  12 . After the fixation of the toner image to the sheet  12 , the sheet  12  is discharged into a delivery tray  20 . Designated by a referential code  17  is a door for allowing a user (operator) of the image forming apparatus  1  to access the interior of the apparatus  11  when the apparatus  11  becomes jammed with the sheet  12  of recording medium or the like. Thus, the door  17  coincides in position to the portions of the recording medium passages, which are prone to recording medium jam or the like. 
       &lt;Fixing Apparatus&gt; 
       [0021]    Next, referring to  FIGS. 2-6 , the aforementioned fixing apparatus  18  is described. 
         [0022]      FIG. 2  is a schematic sectional view of the fixing apparatus  18 , and shows the structure of the apparatus  18 . This fixing apparatus  18  has: a fixation film  27 ; a pressure roller  28 ; and a heater (ceramic heater)  25  which is in contact with the inward surface of the fixation film  27 . The fixing apparatus  18  has also: a thermistor  26  which detects the temperature of the heater; and an entrance guide (guiding member)  30  as a means for guiding a sheet of recording medium into the fixing apparatus  18 . The entrance guide  30  is at the sheet entrance of the recording medium passage of the fixing apparatus  18 , and guides a sheet of recording medium as the sheet enters the fixing apparatus  18 . The fixing apparatus  18  has also a shutter  23 , which is on the opposite side of the recording medium passage from the entrance guide  30 , that is, the portion of the fixing apparatus  18 , through which a sheet of recording medium is introduced into the fixing apparatus  18  along a sheet guide  16 . The shutter  23  is rotatable about an axis X. The position of the shutter  23 , which is indicated by a solid line in  FIG. 2 , is where the shutter  23  is when the recording medium entrance of the fixing apparatus  18  is open, and the position of the shutter  23 , which is indicated by dotted line  FIG. 2 , is when the recording medium entrance is closed. An arrow mark D indicates the direction in which a sheet of recording medium is conveyed. Designated by a referential number  33  is a guide for guiding a sheet  12  of recording medium after fixation. Designated by a referential number  34  is a pair of rollers for conveying a sheet  12  of recording medium into the delivery tray  20 . The fixation film  27  is a thin endless belt, and is formed of polyimide, SUS, or the like. It is 20 mm in external circumference, and 60 μm in thickness. Thus, it is low in thermal capacity, being therefore enabled to be quickly increased in temperature. In order to make it easier for a sheet  12  of recording medium to be parted from the fixation film  27 , the substrate layer of the film  27 , which is made up of polyimide, SUS, or the like, is covered with a parting layer on the outward side. 
         [0023]    The pressure roller  28  is made up of a metallic core and an elastic surface layer. The metallic core is made of iron, stainless steel, or the like substance. The surface layer is cylindrical and covers virtually entirety of the peripheral surface of the metallic core. It is made of solid or foamed silicone rubber. 
         [0024]    The entrance guide  30  is formed of a moldable substance or the like.  FIG. 3  is a plan view of the guide  30  (shown in  FIG. 2 ) as seen from the upstream side of the recording medium conveyance direction. Referring to  FIG. 3 , the entrance guide  30  has: a flat portion  32 ; and multiple ribs  31  (conveyance ribs) which project from the flat portion  32  in the direction perpendicular to the flat surface of the flat portion  32 , and also, in the direction parallel to the recording medium conveyance direction. The ribs  31  are parallel to each other. In other words, the entrance guide  30  is roughly in the form of a comb. The sheet  12  of recording medium, which hereafter may be referred to simply as a sheet  12 , is conveyed into the fixing apparatus  18  in the direction indicated by an arrow mark D. While the sheet  12  is conveyed into the fixing apparatus  18 , it comes into contact with the ribs  31 , but, does not with the flat portion  32 . These ribs  31  are positioned so that when the shutter  23  is in its closed position, that is, the position in which the shutter  23  is closest to the entrance guide  30 , the ribs  31  faces the base portion  29  of the shutter  23  (which will be described later), which does not have projection  24 . 
         [0025]      FIG. 4  is a perspective view of the guide  30  and shutter  23  (when the shutter  23  is in its closed position, being smallest in its distance from guide  30 ). The shutter  23  also is formed of a moldable substance or the like. The main portion of the shutter  23  is long and narrow. The shutter  23  has multiple projections  24  (equivalent to ribs of guide  30 ), which project from the base portion  29  of the shutter  23 . The positioning of these projections  24  is such that when the shutter  23  is in its closest position to the entrance guide  30 , the projections  24  face the flat portion  32  of the entrance guide  30 . That is, in terms of the direction perpendicular to the recording medium conveyance direction, the projections  24  are on the portions of the shutter  23 , which correspond in position to the portions of the guiding member  30 , which do not have the rib  31 . Further, it is desired that the projections  24  are positioned so that when the shutter  23  is in its closed position, they are in the adjacencies of the ribs  31  of the entrance guide  30 , one for one. 
         [0026]    The height of each projection  24  from the base portion  29  of the shutter  23  is greater than the height of each rib  31  from the flat portion  32  of the guide  30 . 
         [0027]    Next, referring to  FIGS. 5 and 6 , the main frame is provided with a pair of stoppers  35  (shutter positioning portions), which are on the outward sides of the guide  30 , one for one, in terms of the lengthwise direction of the guide  30 . The stoppers  35  are the portions of the main frame, which the lengthwise ends of the shutter  23  come into contact as the shutter  23  is closed. Each stopper  35  is in the form of a piece of flat plate. Further, the stoppers  35  are outside the passage of the recording medium sheet  12  in terms of the lengthwise direction of the guide  30 . That is, in terms of the direction perpendicular to the recording medium conveyance direction, there are shutter positioning portions, which are outside the recording medium conveyance passage, and which properly position the shutter  32  as the shutter  23  is moved into the position in which the shutter  23  keeps the recording medium conveyance passage shut. 
       &lt;Movement of Fixing Apparatus Shutter&gt; 
       [0028]    Next, the movement of the shutter  23  of the fixing apparatus  18  is described. 
         [0029]    While the image forming apparatus  1  is forming images, the recording medium sheet  12  is sent to the fixing apparatus  18  after the transfer of a toner image onto the sheet  12 . As heat is applied to the sheet  12  and the toner image thereon by the fixing apparatus  18 , the toner image becomes semi-permanently fixed to the sheet  12 . After the sheet  12  comes out of the fixation nip, the sheet  12  is conveyed along the guide  33  by the pair of discharge rollers  34 , and is discharged into the delivery tray  20 , by the pair of discharge rollers  34 . 
         [0030]    While the recording medium sheet  12  is conveyed through the fixing apparatus  18 , the fixing apparatus  18  keeps its recording medium conveyance passage open by keeping its shutter  23  in the position outlined by the solid line in  FIG. 2 . 
         [0031]    On the other hand, when a user has to deal with a paper jam or the like problem, the user is to open the door  17  of the image forming apparatus  1 , shown in  FIG. 1 , and access the jammed paper in the recording medium conveyance passage. The image forming apparatus  1  and its fixing apparatus  18  are structured so that as the use opens the door  17 , the shutter  23  of the fixing apparatus  18  is moved into its closed position outlined by the dotted line in  FIG. 2 , by the movement of the door  17 , whereby the fixation film  27  and pressure roller  28  are prevented from being touched by the user while a paper jam or the like problem is dealt with. As the user closes the door  17 , the shutter  23  is moved back into its open position by the movement of the door  17 . 
         [0032]      FIG. 6  is a plan view of the entrance guide and shutter of the fixing apparatus  18 , as seen from the upstream side of the fixing apparatus in terms of the recording medium conveyance direction.  FIG. 7  is a sectional view of the entrance guide and shutter of the fixing apparatus  18 , at a plane A-A in  FIG. 6 , which coincides in position with one of the ribs  31  and is perpendicular to the lengthwise direction of the fixing apparatus  18  (perpendicular to recording medium conveyance direction).  FIG. 8  is a sectional view of the entrance guide and shutter of the fixing apparatus, at a plane B-B in  FIG. 6 , which coincides in position with one of the projection  24  of the shutter  23 . First, referring to  FIG. 6 , as the shutter  23  is closed, the lengthwise end portions of the shutter  23  come into contact with the stoppers  35  which are outside the recording medium passage, whereby the shutter  23  is properly positioned in its closed position. Next, referring to  FIG. 7 , the fixing apparatus  18  is structured so that when the shutter  23  is in its closed position, there is a clearance C 1  (space) between each rib  31  of the entrance guide  30  and the base portion of the shutter  23 . 
         [0033]    Next, referring to  FIG. 8 , the fixing apparatus  18  is structured so that when the shutter  23  is in its closed position, there is a clearance C 2  (space) between each of the projection  24  of the shutter  23 , and the flat portion  32  of the entrance guide  30 . 
         [0034]    In a case where the shutter  23  has been bent or warped by external force or the like, as the shutter is rotationally moved into its closed position, the projections  24  of the shutter  23  come into contact with the flat portion  32  (which faces shutter  23 ) of the entrance guide  30 , whereby the shutter  23  is prevented from being rotationally moved further. 
         [0035]    Here, the height of each of the projections  24  of the shutter  23  from the base portion  29  of the shutter  23  is greater than the height of the each of the ribs  31  of the flat portion  32  of the guide  30 , as described previously. Further, the fixing apparatus  18  is structured so that Clearance C 1  is greater than Clearance C 2  (C 1 &gt;C 2 ), as shown in  FIGS. 7 and 8 . That is, when the shutter  23  is in its position in which it keeps closed the entrance of the recording medium passage, Clearance C 1 , that is, the gap between the rib  31  and shutter  23 , is greater than Clearance C 2 , that is, the gap between the guide  30  and projection  24 . Therefore, even if the shutter  23  will have deformed and caused its projections  24  to come into contact with the flat portion  32  of the guide  30 , there will still remain a gap between the ribs  31  and base portion  29 . Therefore, it does not occur that the ribs  31  are damaged by the contact between the ribs  31  (with which sheet  12  of recording medium comes into contact) and shutter  23 . Therefore, the shutter  23  can fulfill its function as a shutter. As for the flat portion  32  of the guide  30 , it is the portion with which the sheet  12  of recording medium is unlikely to come into contact. Therefore, even if the flat portion  32  happens to be damaged by the projections  24 , the portion (tip) of each rib  31 , which comes into contact with the sheet  12 , is protected. Therefore, the fixing apparatus  18  is prevented from suffering from such problems that cause the fixing apparatus  18  to reduce in the accuracy with which the sheet  12  is conveyed through the fixing apparatus  18 , for example, the problem that the fixing apparatus  18  is likely to be jammed with the sheet  12  of recording medium. 
         [0036]    Further, the shutter  23  is provided with the multiple projections  24 . Therefore, if the shutter  23  happens to bend or warp, the shutter  23  is properly supported (at multiple points). In other words, even if the shutter  23  is relatively easily bend in the direction perpendicular to its lengthwise direction, it is possible for the shutter  23  to perform its primary function. Moreover, it is unnecessary for the shutter  23  to be provided with a metallic reinforcement stay or the like for preventing the shutter  23  from bending or warping. Therefore, the shutter  23  may be formed of inexpensive moldable substance. Further, it is unnecessary to increase the shutter  23  in dimensional accuracy in order to prevent the shutter  23  from warping. In other words, the present invention can reduce the shutter  23  in cost. 
         [0037]    Further, when the shutter  23  is stationary in its closed position, its projections  24  are in contact with the flat portion  32  of the guide  30 . Therefore, it is ensured that even if the shutter  23  warps substantially, the ribs  31  are not going to be damaged. 
         [0038]    Incidentally, in this embodiment of the present invention, the shutter  23  was in the adjacencies of the recording medium entrance of the fixing apparatus  18 . However, this embodiment is not intended to limit the present invention in scope. For example, the present invention is also applicable to an image forming apparatus structured so that the shutter of its fixing apparatus  18  is in the adjacencies of the recording medium outlet of the fixing apparatus  18  (downstream end of recording medium passage in fixing apparatus  18  in terms of recording medium conveyance direction), and an image forming apparatus structured so that its fixing apparatus  18  has two shutters which are in the adjacencies of the recording medium entrance and outlet, one for one, of the fixing apparatus  18 . 
         [0039]    Also in this embodiment, the fixing apparatus  18  was for a monochromatic laser printer. However, the application of the present invention is not limited to fixing apparatuses which are the same as, or similar to, the fixing apparatus in this embodiment. That is, the present invention is also applicable to image forming apparatuses other than the one in this embodiment. For example, it is also applicable to a color laser printer or the like. 
         [0040]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
         [0041]    This application claims priority from Japanese Patent Application No. 035532/2010 filed Feb. 22, 2010 which is hereby incorporated by reference.