Patent Publication Number: US-11640131-B2

Title: Fixing device including insulating member with slit formed with projection projecting from one end surface toward the other of slit, and image forming apparatus with fixing device

Description:
INCORPORATION BY REFERENCE 
     This application claims priority to Japanese Patent Application No. 2021-046990 filed on 22 Mar. 2021, the entire contents of which are incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to fixing devices and image forming apparatuses equipped with fixing devices. 
     Generally, a fixing device is known that includes a fixing roller capable of being heated by a heating part and a pressure roller pressed against the fixing roller and fixes a toner image on a sheet by allowing the sheet to pass through a nip formed between both the rollers. In relation to such a general fixing device, there is known a technique in which an annular insulating member is disposed between a shaft of the fixing roller and a bearing supporting the shaft. There is also known a technique in which an insulating member is further provided between a shaft of the pressure roller and a bearing supporting the shaft. 
     The insulating member has a slit formed widthwise at a circumferential location on the insulating member in order to prevent backlash of the fixing roller due to breakage of the insulating member caused by thermal expansion and contraction of the fixing roller. Thus, the insulating member has a circumferential discontinuity created by the slit. 
     SUMMARY 
     A technique improved over the aforementioned techniques is proposed as one aspect of the present disclosure. 
     A fixing device according to an aspect of the present disclosure includes a fixing roller, a pressure roller, a first bearing, a second bearing, and an annular insulating member. The fixing roller includes a heating part and is capable of being heated by the heating part. The pressure roller is pressed against the fixing roller. The first bearing supports a shaft of the fixing roller to allow rotation of the shaft of the fixing roller. The second bearing supports a shaft of the pressure roller to allow rotation of the shaft of the pressure roller. The insulating member is interposed at least one of between the first bearing and the shaft of the fixing roller and between the second bearing and the shaft of the pressure roller. The insulating member has a slit formed in at least one circumferential location thereon and creating a circumferential discontinuity in the insulating member, and includes a projection projecting from one of circumferentially opposed end surfaces of the slit toward the other of the circumferentially opposed end surfaces. 
     An image forming apparatus according to another aspect of the present disclosure includes the above-described fixing device and an image forming device. The image forming device forms an image on a recording medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view showing a schematic structure of an image forming apparatus according to an embodiment of the present disclosure. 
         FIG.  2    is a perspective view showing a fixing roller and a sheet-metal frame supporting the fixing roller. 
         FIG.  3    is a cross-sectional view taken along the line in  FIG.  2   . 
         FIG.  4    is a perspective view showing an insulating member fitted around one end portion of the fixing roller. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a description will be given of an embodiment of the present disclosure with reference to the drawings. However, the present disclosure is not limited to the following embodiment. 
     &lt;Image Forming Apparatus&gt; 
       FIG.  1    is a cross-sectional view showing a schematic structure of an image forming apparatus  1  according to one embodiment of the present disclosure. 
     As shown in  FIG.  1   , the image forming apparatus  1  includes a box-shaped apparatus body  2 , a cassette sheet feeder  4 , an image forming device  5 , an fixing device  6 , and a sheet output device  10 . The image forming apparatus  1  conveys a sheet as a recording medium along a conveyance path in the apparatus body  2  and forms, in the course of conveyance of the sheet, a toner image on the sheet based on image data sent from a terminal device or the like. 
     The cassette sheet feeder  4  is provided at the bottom of the apparatus body  2 . The cassette sheet feeder  4  includes: a sheet feed cassette  11  containing a plurality of sheets stacked one on another; and a pick-up roller  12  capable of picking up the sheets in the sheet feed cassette  11  sheet by sheet. 
     The image forming device  5  is provided above the cassette sheet feeder  4  in the interior of the apparatus body  2 . The image forming device  5  includes: a photosensitive drum  16  as an image carrier rotatably provided in the apparatus body  2 ; a charging roller  17  disposed next to the photosensitive drum  16 ; a developing device  18 , a transfer roller  19 , a cleaning device  20 , and an optical scanning device  30  disposed lateral to the photosensitive drum  16 . The image forming device  5  forms an image on a sheet fed from the cassette sheet feeder  4 . 
     In the conveyance path, a pair of registration rollers  15  are provided to temporarily keep the sheet fed from the sheet feed cassette  11  near the image forming device  5  and then feed the sheet forward to the image forming device  5  with a predetermined timing. 
     The fixing device  6  is disposed above the image forming device  5 . The fixing device  6  includes a fixing roller  22  and a pressure roller  23  which rotate while being pressed against each other. The fixing device  6  fixes the toner image transferred to the sheet by the image forming device  5  on the sheet. 
     The sheet output device  10  is provided obliquely above the fixing device  6 . The sheet output device  10  includes a sheet output tray  3 , a sheet output roller  24  that conveys a sheet to the sheet output tray  3 , and a conveyance guide rib  25  that guides the sheet to the sheet output roller  24 . The sheet output tray  3  is formed in a depressed shape on the top of the apparatus body  2 . 
     When the image forming apparatus  1  receives image data, the photosensitive drum  16  of the image forming device  5  is driven into rotation and the charging roller  17  thereof electrically charges the surface of the photosensitive drum  16 . 
     Subsequently, the optical scanning device  30  emits laser light to the photosensitive drum  16  based on the image data. When the laser light is applied to the surface of the photosensitive drum  16 , an electrostatic latent image is formed on the surface of the photosensitive drum  16 . Meanwhile, a toner is supplied from a toner container  21  to the developing device  18 . The electrostatic latent image formed on the photosensitive drum  16  is developed into a visible image as a toner image by the developing device  18 . 
     Subsequently, the sheet passes between the transfer roller  19  and the photosensitive drum  16 . In doing so, the toner image on the photosensitive drum  16  is transferred to the sheet by a transfer bias transferred to the transfer roller  19 . The sheet having the toner image transferred thereto is subjected to heat and pressure by the fixing roller  22  and the pressure roller  23  in the fixing device  6 . As a result, the toner image is fixed on the sheet. 
     &lt;Fixing Device&gt; 
     The fixing device  6  includes the fixing roller  22 , the pressure roller  23 , and a housing  26 . The housing  26  has an approximately cuboidal shape elongated in a front-to-rear direction. The fixing roller  22  and the pressure roller  23  are accommodated in the housing  26  to extend in the front-to-rear direction. 
     As shown in  FIG.  2   , the fixing roller  22  is rotatably supported through bearings  28  (an example of the first bearing) by a pair of sheet-metal frames  27  provided in the housing  26 . Although in  FIG.  2    the pressure roller  23  (shown only in  FIG.  1   ) is omitted and unshown, it is actually disposed at the upper right of the fixing roller  22 . 
     As shown in  FIG.  3   , the fixing roller  22  includes a cylindrical core  22   c , a releasable layer provided on the outer periphery of the core  22   c  with an adhesive layer in between, and shafts  22   a  protruding from both axial end surfaces of the cylindrical core  22   c . The fixing roller  22  is internally provided with a halogen heater  29  (an example of the heating part). The halogen heater  29  emits radiation heat to the inner periphery of the fixing roller  22  to heat the fixing roller  22 . The shafts  22   a  of the fixing roller  22  are rotatably supported by respective bearings  28  attached to the pair of sheet-metal frames  27 . In this example, the bearings  28  are rolling bearings and are fixed by press fitting to respective attachment holes formed in the sheet-metal frames  27 . 
     An insulating member  40  is interposed between each of the shafts  22   a  of the fixing roller  22  and the associated bearing  28 . The fixing roller  22  is driven into rotation counterclockwise in  FIGS.  1  and  2    by a motor. The pressure roller  23  includes a shaft  23   a , an elastic layer provided on the outer periphery of the shaft  23   a , and a releasable layer provided on the outer periphery of the elastic layer with an adhesive layer in between. The shaft  23   a  of the pressure roller  23  is rotatably supported at both ends by respective bearings  31  attached to the pair of sheet-metal frames  27 . The pressure roller  23  is pressed against the fixing roller  22  by a biasing mechanism. The pressure roller  23  and the fixing roller  22  form a nip therebetween through which a sheet is passed. 
     [Structure of Insulating Member] 
     As shown in  FIG.  4   , each of the insulating members  40  is made of, for example, PPS (polyphenylene sulfide) or PEEK (polyether ether ketone). The insulating member  40  includes: a cylindrical sleeve  40   a  fitted on the shaft  22   a  of the fixing roller  22 ; and a flange  40   b  extending radially outward from one axial end of the sleeve  40   a.    
     As shown in  FIG.  3   , abutment of the flanges  40   b  on the end surfaces of the bearings  28  restricts axially inward movement of the fixing roller  22 . An annular groove  22   b  is formed in each of the shafts  22   a  of the fixing roller  22  and a C-ring  13  is fitted into the annular groove  22   b . The C-ring  13  restricts axially outward movement of the associated insulating member  40 . 
     The cylindrical sleeve  40   a  of the insulating member  40  has a slit  40   c  formed to extend in the axial direction. Thus, the insulating member  40  has a circumferential discontinuity created by the slit  40   c . A projection  40   f  is formed on one end surface  40   d  of both opposed end surfaces  40   d  and  40   e  of the slit  40   c  (in this example, the end surface  40   d  thereof located downstream in a direction of rotation of the fixing roller  22 ). 
     The projection  40   f  projects from the one end surface  40   d  toward the other end surface  40   e . In this example, the projection  40   f  has a semicircular disc shape as viewed in a radial direction of the fixing roller  22 . The projection  40   f  is formed on a central portion of the one end surface  40   d  in a direction along the roller axis (in the axial direction of the fixing roller  22 ). A projecting top surface of the projection  40   f  (i.e., an end surface of the projection  40   f  formed in the shape of a cylindrical surface) abuts on the other end surface  40   e  of the slit  40   c  in a normal temperature condition before the halogen heater  29  is operated. 
     Effects 
     The general fixing device described previously has a problem in that, during rotation of the fixing roller, both the opposed end surfaces of the insulating member with a slit in between rub against each other and thus generate abnormal noise. Specifically, when the amount of thermal expansion of the fixing roller is sufficiently large, both the end surface of the slit come into close contact with each other and, therefore, generate no abnormal noise. However, when the temperature of the fixing roller is relatively low, i.e., when the amount of thermal expansion of the fixing roller is relatively small and the width of the slit in the insulating member becomes narrow, both the end surfaces of the slit may butt against each other during rotation of the fixing roller and, therefore, are likely to rub against each other, which makes the above problem particularly significant. 
     To cope with the above problem, in this embodiment, the insulating member  40  has a slit  40   c  formed in at least one circumferential location thereon and creating a circumferential discontinuity in the insulating member  40 . The insulating member  40  includes a projection  40   f  formed on one end surface  40   d  of circumferentially opposed end surfaces  40   d  and  40   e  of the slit  40   c  and projecting toward the other end surface  40   e.    
     In this structure, since the slit  40   c  is formed in the insulating member  40 , backlash in the shafts  22   a  of the fixing roller  22  due to thermal expansion and contraction can be reduced. In addition, since the projection  40   f  is formed on the one end surface  40   d  of the slit  40   c , this minimizes the area where both the end surfaces  40   d  and  40   e  opposed with the slit  40   c  in between rub against each other during rotation of the fixing roller  22 . As a result, the occurrence of abnormal noise due to rubbing of both the end surfaces  40   d  and  40   e  can be reduced. 
     Furthermore, in this embodiment, the projection  40   f  is formed to make line contact with the other end surface  40   d  of the slit  40   c.    
     In this structure, when the amount of thermal expansion of the fixing roller  22  is relatively small and the width of the slit  40   c  in the insulating member  40  becomes narrow, the projection  40   f  and the other end surface  40   d  of the slit  40   c  are the first to make contact with each other. Therefore, the area of contact between the one end surface  40   d  and the other end surface  40   e  of the slit  40   c  can be reduced as much as possible. As a result, the occurrence of abnormal noise can be more certainly reduced. 
     Specifically, the projection  40   f  is formed with the shape of a cylindrical surface to allow line contact with the other end surface  40   e  of the slit  40   c.    
     In this structure, the projection  40   f  can be prevented from making edge contact with the other end surface  40   e  of the slit  40   c . As a result, the occurrence of abnormal noise can be more certainly reduced. 
     In this embodiment, the projection  40   f  is formed on the central portion of the one end surface  40   d  of the slit  40   c  in the axial direction of the fixing roller  22 . 
     In this structure, the shape of the slit  40   c  can be always held in a rectangular shape extending in the axial direction of the fixing roller  22 . As a result, it can be avoided that, for example, the slit  40   c  deforms in a V-shape to invite edge contact which is widespread contact between the one end surface  40   d  and the other end surface  40   e.    
     In this embodiment, the image forming apparatus  1  includes the fixing device  6  and the image forming device  5 . 
     In this structure, it can be prevented that abnormal noise is caused by rubbing of both the end surfaces  40   d  and  40   e  of the slit  40   c  in the insulating member  40  after the image forming apparatus  1  is started up and, particularly, before the temperature of the fixing roller  22  sufficiently increases. As a result, it can be avoided that the user hears abnormal noise due to rubbing of the insulating member  40  and is thus misled into thinking that a failure has occurred. 
     Other Embodiments 
     Although in the above embodiment the insulating member  40  is provided between each of the shafts  22   a  of the fixing roller  22  and the bearing  28 , the present disclosure is not limited to the manner described in the above embodiment. The insulating member  40  is sufficient to be provided at least one of between the fixing roller  22  and the bearing  28  and between the shaft  23   a  of the pressure roller  23  and the bearing  31  (corresponding to the second bearing). Although in the above embodiment the number of slits  40   c  provided is one, the number of slits  40   c  may be two or more. In this case, the insulating member  40  has a plurality of discontinuities, but the present disclosure can also be applied to this structure. 
     Although in the above embodiment the projection  40   f  formed on one end surface  40   d  of the slit  40   c  in the insulating member  40  is formed to make line contact with the other end surface  40   e , the present disclosure is not limited to the manner described in the above embodiment. For example, the projection  40   f  may be formed to make point contact with the other end surface  40   e . In this case, the end surface of the projection  40   f  is preferably formed in a spherical shape. Thus, the contact area between the projection  40   f  and the other end surface  40   e  can be minimized to reduce the occurrence of abnormal noise. 
     Although in the above embodiment the end surface (the one end surface  40   d ) of the slit  40   c  on which the projection  40   f  is formed is located downstream of the other end surface  40   e  in the direction of rotation of the fixing roller  22 , the present disclosure is not limited to the manner described in the above embodiment. For example, the end surface of the slit  40   c  having the projection  40   f  may be located upstream of the other end surface  40   e  in the direction of rotation of the fixing roller  22 . 
     INDUSTRIAL APPLICABILITY 
     As seen from the above, the present disclosure is useful for a fixing device and an image forming apparatus equipped with a fixing device and particularly useful for applying to an image forming apparatus, such as a printer, a facsimile machine or a multifunction peripheral (MFP). 
     While the present disclosure has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art the various changes and modifications may be made therein within the scope defined by the appended claims.