Patent Publication Number: US-11029633-B2

Title: Fixing device and image forming apparatus incorporating same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119 to Japanese Patent Application No. 2018-223414, filed on Nov. 29, 2018 in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure generally relate to a fixing device and an image forming apparatus incorporating the fixing device. 
     Background Art 
     Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium. 
     Such a fixing device may include a fixing rotator, such as a fixing roller, a fixing belt, and a fixing film, heated by a heater and a pressure rotator, such as a pressure roller and a pressure belt, pressed against the fixing rotator to form a fixing nip therebetween through which a recording medium bearing a toner image is conveyed. As the recording medium bearing the toner image is conveyed through the fixing nip, the fixing rotator and the pressure rotator apply heat and pressure to the recording medium, melting and fixing the toner image on the recording medium. 
     SUMMARY 
     This specification describes an improved fixing device that includes a rotatable fixing belt, a pressure rotator, and a belt polishing mechanism. The rotatable fixing belt is stretched taut around a plurality of supports. The pressure rotator is configured to form a fixing nip between the fixing belt and the pressure rotator. The belt polishing mechanism is configured to polish a surface of the fixing belt and includes a polishing roller, a contact and separation driver, an opposed member, and a polishing roller rotation mechanism. The polishing roller is configured to separably contact the fixing belt and slide over the surface of the fixing belt when the polishing roller is pressed against the fixing belt. The contact and separation driver is configured to press and separate the polishing roller to and from the fixing belt. The opposed member is disposed opposite the polishing roller via the fixing belt and configured to form a polishing nip with the fixing belt. The polishing roller rotation mechanism is configured to rotate the polishing roller and includes a first rotator disposed coaxially with the polishing roller and a second rotator disposed coaxially with the opposed member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure would be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram illustrating a configuration of a comparative fixing device having a polishing roller; 
         FIG. 2  is a schematic diagram illustrating a configuration of an example of a fixing device according to an embodiment of the present disclosure; 
         FIG. 3  is an explanatory diagram illustrating an arrangement of a polishing roller rotation mechanism in the fixing device of  FIG. 1 ; 
         FIG. 4  is an explanatory diagram illustrating an arrangement of the polishing roller rotation mechanism in the fixing device according to an embodiment of the present disclosure; 
         FIG. 5  is a schematic diagram illustrating a configuration of an example of the fixing device according to an embodiment of the present disclosure, in which the polishing roller is pressed against a fixing belt to change a rotation locus of the fixing belt; and 
         FIG. 6  is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result. 
     Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings illustrating the following embodiments, the same reference numbers are allocated to elements having the same function or shape and redundant descriptions thereof are omitted below. 
     In an electrophotographic image forming apparatus, toner image is transferred onto a recording medium such as a sheet, and the fixing device fixes the toner image onto the recording medium by heat and pressure and conveys the recording medium. 
     The fixing device generally includes a fixing roller and a pressure roller, and the fixing device in, e.g., a commercial printer includes a fixing belt to achieve high-speed printing, maintain a heat storage capability, and fix a toner image onto a sheet even if the sheet has an uneven surface. 
     A description is provided of a configuration of a comparative fixing device. An electrophotographic image forming apparatus forms toner images of various sizes on sheets of various sizes and thicknesses. 
     After a plurality of small sheets is conveyed through the comparative fixing device, when a large sheet is conveyed through the comparative fixing device, a fixing belt may generate a gloss streak on the toner image on the large sheet at a portion of the fixing belt over which a lateral edge of the small sheets has slid. While the small sheets are conveyed over the fixing belt, the lateral edge of the small sheets may damage the fixing belt with a streaked scratch. Since burrs on a machined edge of the small sheet produce the streaked scratch on the fixing belt, the streaked scratch on the fixing belt is conspicuous as the number of the small sheets conveyed over the fixing belt increases. 
     Exchanging the fixing belt deletes the gloss streak, but to reduce time and cost required to exchange the fixing belt, the comparative fixing device includes a polishing roller that restores the fixing belt damaged with the streaked scratch. The polishing roller polishes the fixing belt, removes the scratches on the fixing belt, prevents the occurrence of the gloss streaks, and lengthens a life of the fixing belt. 
     During maintenance, a spring and a cam press the polishing roller against the fixing belt to polish the fixing belt, and after maintenance, for example, during printing, the polishing roller separates from the fixing belt. Therefore, in order to shorten the polishing time and prevent the occurrence of a polishing deviation in a width direction of the fixing belt, adjusting the pressure of the polishing roller is important. 
     However, the state of the fixing belt and the state of the polishing roller are not always constant. In addition, to reduce the polishing time and obtain the desired polishing, the fixing device may have different polishing modes such as use of multiple polishing rollers having different surface roughness. The load required for polishing in each case is not constant. Therefore, adjusting the polishing roller is needed in each case. Changing the design of the fixing device slightly also requires adjustment of the polishing roller. 
       FIGS. 1 to 4  illustrate schematic configurations of fixing devices having polishing rollers.  FIGS. 1 and 3  illustrate the comparative fixing device, and  FIGS. 2  and  4  illustrate a fixing device according to an embodiment of the present disclosure. 
     Each of the fixing device  25  according to the present embodiment and the comparative fixing device  25 C includes a fixing belt  26  stretched around a plurality of supports and configured to rotate, a pressure rotator  27  such as a pressure roller that forms a fixing nip with the fixing belt  26 , and a belt polishing mechanism  50  configured to polish the surface of the fixing belt  26 . 
     The belt polishing mechanism  50  is provided so as to contact and separate from the fixing belt  26 . The belt polishing mechanism  50  includes the polishing roller  51  configured to slide over the surface of the fixing belt  26  when the polishing roller  51  is pressed against the fixing belt  26 , a contact and separation driver configured to press and separate the polishing roller  51  to and from the fixing belt  26 , an opposed member such as an opposed rotator disposed opposite the polishing roller  51  via the fixing belt  26  to form a polishing nip with the fixing belt  26 , and a polishing roller rotation mechanism configured to rotate the polishing roller  51 . 
     The plurality of supports to stretch the fixing belt  26  includes a fixing roller  29  disposed opposite the pressure rotator  27  via the fixing belt  26  to form the fixing nip between the pressure rotator  27  and the fixing belt  26  and a heating roller  30  to heat the fixing belt  26 . The heating roller  30  includes a heater  31  inside. 
     In addition, in order to apply tension to the fixing belt  26 , a spring urges the heating roller  30  in a direction indicated by an arrow  32 . 
     The belt polishing mechanism  50  is disposed near an opposed rotator  37 . 
     The opposed rotator  37  may be at least one of the plurality of supports or may be a fixed member separate from the plurality of supports. 
     When the opposed rotator  37  is one of the supports, the opposed rotator  37  is preferably the fixing roller  29  that presses against the pressure rotator  27  via the fixing belt  26  to form the fixing nip between the fixing belt  26  and the pressure rotator  27 . 
     Hereinafter, an aspect in which the opposed rotator  37  is the fixing roller  29  is described. 
     A polishing unit includes the polishing roller  51  to polish the fixing belt  26 , a swing  53  to press the polishing roller  51  against the fixing belt  26 , a holder  52  to hold the polishing roller  51 , and the polishing roller rotation mechanism to rotate the polishing roller  51 . 
     The polishing roller rotation mechanism includes a first rotator disposed coaxially with the polishing roller  51  to drive the polishing roller  51 , hereinafter referred to as a “polishing roller drive gear  34 ”, and a second rotator to transmit a driving force from a drive source (for example, a motor) to the first rotator, hereinafter referred to as a “drive transmission gear  35 ”. 
     The polishing roller drive gear  34  is disposed on one side of the polishing roller  51  not to interfere with the fixing belt  26 . 
     As illustrated in  FIGS. 1 and 3 , the comparative fixing device  25 C includes the drive transmission gear  35  as the second rotator that is arranged on the circumference of the polishing roller drive gear  34  as the first rotator. 
     The drive transmission gear  35  is disposed at a position that does not overlap the projection surface of the opposed rotator such as the fixing roller  29  to avoid interference with the fixing roller  29  as the opposed rotator. 
     For example, as illustrated in  FIG. 3 , the drive transmission gear  35  is disposed with a shaft serving as the rotation fulcrum at a position at which a pressing direction indicated by an arrow  33  and a center line connecting the center of the polishing roller drive gear  34  and the center of the drive transmission gear  35  intersect at an angle θ. 
     In transmission of the driving force from the drive transmission gear  35  to the polishing roller drive gear  34 , a load to rotate the polishing roller  51  generates a gear meshing force (N) indicated by an arrow  36 . 
     A pressure angle φ determines a direction in which the gear transmits force, and the gear meshing force (N) indicated by the arrow  36  is applied in the direction of 90°+φ with respect to the center line connecting the center of the polishing roller drive gear  34  and the center of the drive transmission gear  35 . 
     Since this gear meshing force (N) indicated by the arrow  36  is applied to the polishing roller  51 , a force represented by the following formula (1) is added to the pressing force of the polishing roller  51 , which generates a deviation of a force corresponding to the value.
 
N sin(θ+φ)  Formula (1)
 
     For example, when N is 10 N, θ is 45°, and φ is 20°, the value of formula (1) is 9.1 N. 
     In contrast, in the fixing device  25  of the present embodiment, as illustrated in  FIGS. 2 and 4 , the polishing roller rotation mechanism includes the polishing roller drive gear  34  as the first rotator disposed coaxially with the polishing roller  51  and the drive transmission gear  35  as the second rotator disposed coaxially with the opposed rotator. 
     In addition to the arrangement of the drive transmission gear  35  disposed coaxially with the opposed rotator  37  that is the fixing roller  29 , related parts are arranged so that the angle θ formed by the pressing direction indicated by the arrow  33  and the center line connecting the centers of the polishing roller drive gear  34  and the center of the drive transmission gear  35  is equal to the pressure angle φ. 
     This arrangement causes the value of the above formula (1) to be 0 regardless of the value of the gear meshing force (N) indicated by the arrow  36 , and the pressing deviation on the polishing roller  51  can be completely eliminated. 
     In the present embodiment, the arrangement of the drive transmission gear  35  disposed coaxially with the opposed rotator  37  that is the fixing roller  29  does not need an independent shaft of the drive transmission gear  35  that serves as a rotation fulcrum. 
     Additionally, in the present embodiment, since the polishing roller  51  and the opposed rotator  37  (fixing roller  29 ) determine the appropriate positions of the gear shaft centers, a mechanism required in the comparative fixing device  25 C is not needed to suitably position the gear shaft centers in the present embodiment. 
     The above-described configuration in the fixing device  25  of the present embodiment enables the polishing roller  51  to uniformly contact and press against the fixing belt  26  to be polished and ensure a sufficient contact area. Therefore, the above-described configuration can reduce the cost and size of the device and the polishing time required for rejuvenating the surface properties and prevent the occurrence of polishing deviations. 
     The fixing belt  26  may be, for example, an endless belt having a multilayer structure in which a release layer and an elastic layer made of silicone rubber or the like are sequentially laminated on a base layer made of polyimide resin (PI) and having a layer thickness of 90 μm. 
     The elastic layer of the fixing belt  26  may have, for example, a layer thickness of about 200 μm and may be formed of an elastic material such as silicone rubber, fluorine rubber, and silicone rubber foam. 
     The release layer of the fixing belt  26  may have, for example, a layer thickness of about 20 micrometers and may be made of tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), polyimide (PI), polyether imide (PEI), polyether sulfide (PES), or the like. Providing the release layer on the surface layer of the fixing belt  26  ensures the releasability (removability) with respect to the toner (toner image) and a good separation performance between the fixing belt  26  and a recording medium such as a sheet having the toner image that is well fixed. 
     The polishing roller  51  includes a core bar  51   a  and a slide layer  51   b  disposed on the core bar  51   a . The slide layer  51   b  serves as an abrasive grain layer or a polishing layer, for example. The slide layer  51   b  as a surface layer includes a binder resin and abrasive grains  51   c  dispersed in the binder resin. The abrasive grains  51   c  project beyond an outer circumferential surface of the slide layer  51   b  to define slight surface asperities. The abrasive grains  51   c  are alumina abrasive grains as general abrasive particles, for example, white fused alumina #1500. Alternatively, the abrasive grains  51   c  may be made of other materials. The grain size of the abrasive grains  51   c  may be identical throughout the entire slide span of the polishing roller  51  that slides over the fixing belt  26 . 
     The heater  31  incorporated in the heating roller  30  may be, for example, a halogen heater or an induction heating (IH) device that is an electromagnetic induction heating device. 
     As described above, the opposed rotator  37  may be at least one of the plurality of supports to stretch the fixing belt  26  or may be a fixed member separate from the plurality of supports. When the opposed rotator  37  is one of the supports, the opposed rotator  37  may be the fixing roller  29 . 
     Preferably, the rotational speed of the opposed rotator  37  that is a rotating member is different from the rotational speed of the drive transmission gear  35  as the second rotator disposed coaxially with the opposed rotator  37 . 
     In addition, preferably the drive transmission gear  35  as the second rotator transmits the driving force to the polishing roller drive gear  34  as the first rotator when the polishing roller  51  is pressed against the fixing belt  26 . 
     This configuration can control the transmission of the driving force so that the driving force is transmitted when the polishing roller  51  is pressed against the fixing belt  26  and not transmitted when the polishing roller  51  separates from the fixing belt  26 . 
     Preferably, the polishing roller  51  is rotationally driven at a speed different from the surface speed of the fixing belt  26  that is rotationally driven. 
     The surface speed of the polishing roller  51  with respect to the surface speed of the fixing belt  26  is not particularly limited and can be selected as appropriate. For example, the polishing roller  51  may rub the surface of the fixing belt  26  at the speed three times faster than the speed of the fixing belt  26  in a forward direction. 
     Accordingly, the polishing roller  51  contacts the fixing belt  26  in the sufficient contact area, improving a polishing quality and decreasing the polishing time taken to restore the outer circumferential surface of the fixing belt  26 . 
     In the fixing device  25  according to the present embodiment, as illustrated in  FIG. 5 , while the polishing roller  51  is pressed against the fixing belt  26 , the polishing roller  51  is disposed opposite the opposed rotator  37  via the fixing belt  26  to form the polishing nip between the polishing roller  51  and the fixing belt  26  and changes a rotation locus of the fixing belt  26  along at least a part of a circumferential face of the polishing roller  51 . 
     Specifically, the polishing roller  51  is preferably set so that a wound angle is equal to or greater than 10° and more preferably set so that the wound angle is equal to or greater than 20°. The wound angle is an angle formed by a straight line connecting a center of the polishing roller  51  and a center of the opposed rotator  37  and a straight line passing through the center of the polishing roller  51  and being perpendicular to the outer circumferential surface of the fixing belt  26 . 
     A surface layer of at least one of the polishing roller  51  and the opposed rotator  37  preferably includes an elastic body. 
     In order to bring the polishing roller  51  into contact with the fixing belt  26 , the polishing roller  51  may move toward the opposed rotator  37  or the opposed rotator  37  may move toward the polishing roller  51 . 
     The polishing roller  51  may be removably attached to the fixing device  25  so that a user attaches the polishing roller  51  to the fixing device  25  to cause the polishing roller  51  to polish the fixing belt  26  and removes the polishing roller  51  when the polishing roller  51  does not polish the fixing belt  26 . 
     With reference to  FIG. 6 , a description is provided of an image forming apparatus including the fixing device according to an embodiment of the present disclosure.  FIG. 6  is a schematic diagram illustrating a configuration of the image forming apparatus. As illustrated in  FIG. 6 , the image forming apparatus  1000  is a printer employing a tandem intermediate transfer system. The image forming apparatus  1000  includes a body  100  and a sheet feed table  200  mounting the body  100 . 
     The body  100  accommodates an image forming section  20  employing the tandem intermediate transfer system (hereinafter referred to as a tandem image forming section). The image forming section  20  includes a plurality of image forming devices  18 Y,  18 M,  18 C, and  18 K aligned horizontally. Suffixes Y, M, C, and K represent yellow, magenta, cyan, and black, respectively. 
     An intermediate transfer belt  10  as an endless belt type intermediate transferor is situated in a sheet conveyance region and in a substantially center portion of the body  100 . The intermediate transfer belt  10  is looped over a plurality of rollers, that is, an intermediate transfer belt driving roller  14 , intermediate transfer belt support rollers  15   a  and  15   b , a secondary-transfer backup roller  16   a , and the like. The intermediate transfer belt  10  is rotatable clockwise in  FIG. 6 . 
     On the left of the secondary-transfer backup roller  16   a , a belt cleaner  17  is disposed to clean the intermediate transfer belt  10 . The belt cleaner  17  removes residual toner remaining on the intermediate transfer belt  10  after the toner image formed on the intermediate transfer belt  10  is transferred. 
     Above an upper face of the intermediate transfer belt  10  stretched taut around the intermediate transfer belt driving roller  14  and the intermediate transfer belt support rollers  15   a  and  15   b , the four image forming devices  18 Y,  18 M,  18 C, and  18 K are aligned horizontally in the rotation direction of the intermediate transfer belt  10  to form yellow, magenta, cyan, and black toner images, respectively, thus constructing the tandem image forming section  20 . The image forming devices  18 Y,  18 M,  18 C, and  18 K, of the tandem image forming section  20  include photoconductive drums  40 Y,  40 M,  40 C, and  40 K serving as image bearers that bear yellow, magenta, cyan, and black toner images, respectively. 
     As illustrated in  FIG. 6 , above the tandem image forming section  20 , two exposure devices  21  are disposed. The left exposure device  21  is disposed opposite the two image forming devices  18 Y and  18 M. The right exposure device  21  is disposed opposite the two image forming devices  18 C and  18 K. For example, each of the exposure devices  21  employs an optical scanning method and includes two light sources (e.g., a semiconductor laser, a semiconductor laser array, or a multi-beam light source), a coupling optical system, a common optical deflector (e.g., a polygon mirror), and two scanning-image forming optical systems. The exposure devices  21  expose the photoconductive drums  40 Y,  40 M,  40 C, and  40 K according to yellow, magenta, cyan, and black image data, forming electrostatic latent images on the photoconductive drums  40 Y,  40 M,  40 C, and  40 K, respectively. 
     Each of the photoconductive drums  40 Y,  40 M,  40 C, and  40 K is surrounded by a developing device and a photoconductive drum cleaner. The developing device visualizes the electrostatic latent image that is formed by a charger and the exposure device  21  into a visible toner image, that is, yellow, magenta, cyan, and black toner images. Before the exposure devices  21  expose the photoconductive drums  40 Y,  40 M,  40 C, and  40 K, the chargers uniformly charge the photoconductive drums  40 Y,  40 M,  40 C, and  40 K, respectively. The photoconductive drum cleaners remove residual toner failed to be transferred onto the intermediate transfer belt  10  and therefore remaining on the photoconductive drums  40 Y,  40 M,  40 C, and  40 K therefrom, respectively. 
     Primary transfer rollers  62 Y,  62 M,  62 C, and  62 K serving as primary transferors are disposed opposite the photoconductive drums  40 Y,  40 M,  40 C, and  40 K via the intermediate transfer belt  10  to form primary transfer nips between the photoconductive drums  40 Y,  40 M,  40 C, and  40 K and the intermediate transfer belt  10 , respectively, where the yellow, magenta, cyan, and black toner images formed on the photoconductive drums  40 Y,  40 M,  40 C, and  40 K are primarily transferred onto the intermediate transfer belt  10  as a color toner image. The primary transfer rollers  62 Y,  62 M,  62 C, and  62 K are disposed opposite the photoconductive drums  40 Y,  40 M,  40 C, and  40 K with the intermediate transfer belt  10  sandwiched between the primary transfer rollers  62 Y,  62 M,  62 C, and  62 K and the photoconductive drums  40 Y  40 M,  40 C, and  40 K, respectively. 
     The intermediate transfer belt driving roller  14  is a driving roller that drives and rotates the intermediate transfer belt  10 . The intermediate transfer belt driving roller  14  is coupled to a motor through a driving force transmitter (e.g., a gear, a pulley, and a belt). In a print job to form a black toner image on the intermediate transfer belt  10 , a mover moves the intermediate transfer belt support rollers  15   a  and  15   b  without moving the intermediate transfer belt driving roller  14 . Thus, the mover isolates the intermediate transfer belt  10  from the photoconductive drums  40 Y  40 M, and  40 C used for forming yellow, magenta, and cyan toner images, respectively. 
     A secondary transfer device  22  is disposed opposite the tandem image forming section  20  via the intermediate transfer belt  10 . In  FIG. 6 , the secondary transfer device  22  includes a secondary transfer roller  16   b  pressed against the secondary-transfer backup roller  16   a  via the intermediate transfer belt  10 . The secondary transfer roller  16   b  generates a transfer electric field to secondarily transfer the color toner image formed on the intermediate transfer belt  10  onto the sheet S as a transfer medium. 
     Downstream from the secondary transfer device  22  in a sheet conveyance direction, the fixing device  25  according to the present disclosure is disposed to fix the color toner image transferred from the intermediate transfer belt  10  onto the sheet S thereon. 
     A conveyance belt  24  supported by two conveyance belt support rollers  23   a  and  23   b  conveys the sheet S bearing the color toner image transferred from the intermediate transfer belt  10  by the secondary transfer device  22  to the fixing device  25 . Instead of the conveyance belt  24 , a stationary guide, a conveyor roller, or the like may be used. 
     Below the secondary transfer device  22  and the fixing device  25 , a sheet reverse device  28  is disposed. The sheet reversing device  28  reverses and conveys the transfer sheet S to record images on both sides of the transfer sheet S in parallel with the tandem image forming section  20  described above. 
     The present disclosure is not limited to the above-described embodiments, and the configuration of the present embodiment can be appropriately modified other than suggested in each of the above embodiments within a scope of the technological concept of the present disclosure. Also, the positions, the shapes, and the number of components are not limited to the embodiments, and they may be modified suitably in implementing the present disclosure. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the above teachings, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims. 
     Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.