Patent Publication Number: US-2011052278-A1

Title: Fusing unit and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C §119(a) from Korean Patent Application No. 2009-0082414, filed on Sep. 2, 2009 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field of the Invention 
     Embodiments of the present general inventive concept relate to an image forming apparatus having a fusing unit to fuse developer to a printing medium. 
     2. Description of the Related Art 
     Image forming apparatuses are devised to form an image on a printing medium according to inputted image signals. Examples of image forming apparatuses include printers, copiers, facsimiles, and devices combining functions thereof. 
     An image forming apparatus includes, e.g., a body defining an outer appearance of the image forming apparatus, a printing medium storage unit in which a plurality of printing media is stored, a developing unit to develop an electrostatic latent image into a visible image by applying developer to the electrostatic latent image, an exposure unit to form an electrostatic latent image on a photosensitive body of the developing unit, a fusing unit to fuse developer, that has been transferred to a printing medium, onto the printing medium, and a discharge unit to discharge a printing medium, on which an image has been completely formed, to an outside of the body. 
     Accordingly, after an electrostatic latent image is formed on a surface of the photosensitive body of the developing unit as light scans the photosensitive body that has been electrically charged, developer is fed to the electrostatic latent image formed on the photosensitive body, developing the electrostatic latent image into a visible image. Subsequently, the visible image formed on the photosensitive body is transferred to a printing medium supplied from the printing medium storage unit and in turn, the transferred image on the printing medium is fused onto the printing medium while passing through the fusing unit. In this way, formation of an image on the printing medium is completed. The printing medium, on which the image has been completely formed, is discharged out of the body via the discharge unit. 
     Of the above mentioned constituent elements of the image forming apparatus, the fusing unit includes a heating roller, a press roller elastically supported on an outer surface of the heating roller, and a pair of discharge rollers to discharge a printing medium, on which an image has been completely fused, from the fusing unit. Accordingly, as a printing medium containing transferred developer passes between the heating roller and the press roller, the developer is fused onto the printing medium by heat and pressure applied by the heating roller and the press roller. Thereafter, the printing medium is discharged out of the fusing unit by passing between the pair of discharge rollers. 
     SUMMARY 
     The present general inventive concept provides a fusing unit to reduce and/or prevent damage to an outer surface of a heating roller due to use for a long period of time and consequently, to reduce and/or prevent deterioration in an image quality, and an image forming apparatus having the same. 
     Additional features and/or utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     Features and/or utilities of the present general inventive concept may be achieved by providing a fusing unit which includes a heating roller, a press roller to press a printing medium toward the heating roller, and a pressure member to apply a face pressure (i.e., a force) to an outer peripheral surface of the heating roller to enable grinding of the outer peripheral surface. 
     The pressure member may extend parallel to a shaft of the heating roller to have a length at least equal to or greater than a width of the printing medium. 
     The pressure member may extend parallel to a shaft of the heating roller to have a length at least equal to or greater than a length of the heating roller. 
     An end of the pressure member may extend in a rotating direction of the heating roller so that a portion of the end is supported on the outer peripheral surface of the heating roller. 
     The pressure member may be formed of an elastically deformable plate and may be elastically supported on the heating roller while being kept bent. 
     A plurality of pressure members may be spaced apart from one another along a circumferential direction of the heating roller. 
     The pressure member may be formed of a metal plate, and the fusing unit may further include a temperature sensor installed onto the pressure member to measure a temperature of the heating roller. 
     The pressure member may be formed of an elastically deformable plate and may be bent arcuately (e.g., shaped in an arc) to be elastically supported on the outer peripheral surface of the heating roller, and the fusing unit may further include supporting members coupled to both ends of the bent pressure member to keep the pressure member in the bent posture (e.g., the arc shape). 
     The pressure member may be formed of a rod shape having a circular cross section. 
     The fusing unit may further include a drive roller to rotate a belt having a first side installed onto the pressure member and a second side installed onto the drive roller. 
     A surface of the belt may contact a face of the outer peripheral surface of the heating roller. 
     Features and/or utilities of the present general inventive concept may also be achieved by providing an image forming apparatus which includes a fusing unit to fuse developer disposed on a printing medium onto the printing medium, wherein the fusing unit includes a heating roller, a press roller to press the printing medium toward the heating roller, and a pressure member to apply a face pressure (i.e., a force) to an outer peripheral surface of the heating roller to enable grinding of the outer peripheral surface. 
     Features and/or utilities of the present general inventive concept may also be achieved by providing a pressure member assembly usable with an image forming apparatus having a heating roller and a pressure roller to press a printing medium toward the heating roller, the pressure member assembly including a pressure member having a first portion in contact with a surface of the heating roller and a second portion supported within the image forming apparatus such that the first portion provides a constant elastic force against the surface of the heating roller. 
     The pressure member may be arc-shaped such that the second portion is spaced apart from the surface of the heating roller. 
     The pressure member may be formed of an elastic material. 
     The surface of the heating roller may be coated with a polymer layer. 
     The constant elastic force may be adjustable to maintain a desired surface roughness of the heating roller. The constant elastic force may be about 200 mPa. 
     Features and/or utilities of the present general inventive concept may also be achieved by providing a pressure member assembly usable with an image forming apparatus having a heating roller which includes a support member disposed adjacent to the heating roller, and a plurality of pressure members coupled to the support member such that a surface of each of the pressure member generates a force against a surface of the heating roller to remove impurities disposed thereon. 
     The force may be adjustable to achieve a desired surface roughness of the heating roller. 
     The plurality of pressure members may be integrally formed with each other. 
     The plurality of pressure members may be formed of an elastic material in an arc-shape. 
     The plurality of pressure members may be formed of a thermally conductive material to transmit heat to the heating roller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other features and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a sectional view illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment of the present general inventive concept; 
         FIG. 2  is a schematic view of a fusing unit usable with an image forming apparatus according to an exemplary embodiment of the present general inventive concept; 
         FIG. 3  is a perspective view of a heating roller and a pressure member illustrated in  FIG. 2 ; 
         FIG. 4  is a schematic view of the pressure member illustrated in  FIG. 3 ; 
         FIG. 5  is a schematic view of a fusing unit usable with an image forming apparatus according to an exemplary embodiment of the present general inventive concept; 
         FIG. 6  is a schematic view of a fusing unit usable with an image forming apparatus according to an exemplary embodiment of the present general inventive concept; 
         FIG. 7  is a schematic view of a fusing unit usable with an image forming apparatus according to a an exemplary embodiment of the present general inventive concept; 
         FIG. 8  is a schematic view of a fusing unit usable with an image forming apparatus according to an exemplary embodiment of the present general inventive concept; and 
         FIG. 9  is a schematic view of a fusing unit usable with an image forming apparatus according to an exemplary embodiment of the present general inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to an image forming apparatus according to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
     As illustrated in  FIG. 1 , an image forming apparatus  100  according to an exemplary embodiment of the present general inventive concept includes a body  10  which defines an outer appearance of the image forming apparatus  100 , a printing medium storage unit  20 , a pickup unit  30 , a developing unit  40 , an exposure unit  50 , and a fusing unit  60 . The printing medium storage unit  20  may be removably installed in the body  10  and stores printing media P, such as paper, therein to supply the printing media P to the developing unit  40 . The pickup unit  30  can be used to pick up the printing media P stored in the printing medium storage unit  20  sheet by sheet. The developing unit  40  can serve to form a visible image on each printing medium P supplied via the pickup unit  30  by use of developer. The exposure unit  50  can serve to form an electrostatic latent image on a photosensitive body  41  of the developing unit  40 . The fusing unit  60  can serve to fuse developer, which has been transferred to a printing medium P, onto the printing medium P, to thereby complete an image formation operation. 
     The printing medium storage unit  20  includes a printing medium cassette  21  and a knock-up plate  22 . The printing medium cassette  21  may be installed in the body  10  so as to be movable in a first direction and a second direction (i.e., forward and reward directions) to be pulled out or pushed into the body  10 , similar to a drawer. The knock-up plate  22  can be installed in the printing medium cassette  21  to load a plurality of printing media P thereon. 
     The pickup unit  30  picks up an uppermost one of the printing media P stored in the printing medium storage unit  20  and delivers the printing media P to the developing unit  40  sheet by sheet. The pickup unit  30  includes a pickup roller  31 , which is adapted to come into frictional contact with a printing medium P stored in the printing medium storage unit  20  during a rotation of the pickup roller  31 , thereby functioning to pick up the printing medium P. 
     The developing unit  40  can form a visible image on a printing medium P delivered from the printing medium storage unit  20  by use of developer, such as toner. The developing unit  40  includes the photosensitive body  41  to serve as an image carrier, on a surface of which an electrostatic latent image is formed by the exposure unit  50 , a charging roller  42  to electrically charge the photosensitive body  41 , and a developing roller  43  to develop the electrostatic latent image formed on the photosensitive body  41  into a visible image. 
     The exposure unit  50  forms an electrostatic latent image on the photosensitive body  41  by scanning light, which may contain image information, onto the photosensitive body  41 . 
     In addition, a transfer roller  11 , an alignment roller  12 , and a plurality of discharge rollers  13  are installed in the body  10 . The transfer roller  11  can be arranged opposite to the photosensitive body  41  and can transfer a visible image formed on the photosensitive body  41  to a printing medium P by pressing the printing medium P toward the photosensitive body  41 . The alignment roller  12  can be used to align a front end of a printing medium P picked up by the pickup roller  31 . The plurality of discharge rollers  13  is successively arranged along a movement path D of a printing medium P, on which an image has been completely formed, and can be used to discharge the printing medium P, having passed through the fusing unit  60 , to an outside of the body  10 . 
     The fusing unit  60  fuses developer onto a printing medium P by applying heat and/or pressure to the printing medium P. The fusing unit  60 , as illustrated in  FIG. 2 , includes a heating roller  61  in which a heater  61   a  is received, and a press roller  62  elastically supported on an outer peripheral surface of the heating roller  61  to press a printing medium P toward the heating roller  61 . A fusing case  63  encloses the heating roller  61  and the press roller  62  and may define an outer appearance of the fusing unit  60 . The heating roller  61  and the press roller  62  may be rotatably installed within the fusing case  63 . 
     In exemplary embodiments, the fusing unit  60  may further include a pressure member  64 , to maintain a surface roughness of the heating roller  61  at a predetermined level or less. In the present exemplary embodiment, the pressure member  64  is made of an elastically deformable material, one side of which is elastically supported on the heating roller  61  while coming into surface contact with an outer peripheral surface A of the heating roller  61  in order to apply a face pressure to at least a partial region of the outer peripheral surface A of the heating roller  61 . 
     The outer peripheral surface A of the heating roller  61  can be formed of a perfluoroalkoxy copolymer layer, and to prevent damage to the perfluoroalkoxy copolymer layer of the outer peripheral surface A of the heating roller  61 , the pressure member  64  is adapted to press against the outer peripheral surface A of the heating roller  61  by a pressure of approximately 200 mPa. However, the present general inventive concept is not limited thereto. That is, in exemplary embodiments, a force applied by the pressure member  64  onto the heating roller  61  may be adjusted to correspond to a force required to remove impurities, such as developer, from the heating roller  61 . In exemplary embodiments, providing the press member  64  to be elastically supported on the outer peripheral surface A of the heating roller  61  in order to apply a face pressure to the outer peripheral surface A of the heating roller  61  has an effect of grinding the outer peripheral surface A of the heating roller  61  and of removing impurities or developer which remain on the surface of the heating roller  61 . Accordingly, the outer peripheral surface A of the heating roller  61  may maintain a surface roughness at a predetermined level or less even after being used for a long period of time. 
     In exemplary embodiments, the pressure member  64 , as illustrated in  FIG. 3 , takes the form of a plate, a front end of which extends in a rotating direction D 1  of the heating roller  61 , so that the front end is elastically bent to come into surface contact with a partial region of the outer peripheral surface A of the heating roller  61 . A supporting member  65  can be coupled to a rear end of the pressure member  64  and can be used to support and fixedly couple the rear end of the pressure member  64  to the fusing case  63 . With this installation of the pressure member  64 , for example, it may be possible to prevent a front end edge of the pressure member  64  from scratching or damaging the outer peripheral surface A of the heating roller  61 . Moreover, even if the heating roller  61  is unintentionally rotated in a reverse direction D 2  during an assembly operation of the fusing unit  60 , the pressure member  64  is maintained to continuously come into surface contact with the outer peripheral surface A of the heating roller  61 , while causing no damage to the heating roller  61 . 
     The pressure member  64  lengthily extends in an axial direction of the heating roller  61 , to have a length at least equal to or greater than a width of a printing medium P. This axially extending pressure member  64  may allow the outer peripheral surface A of the heating roller  61  to have a grinding effect over a wider area than a passage area of the printing medium P. That is, in exemplary embodiments, the pressure member  64  may extend along the axial direction of the heating roller  61  to have a length which is equal to or greater than a length of an area through which the printing medium P passes in between the heating roller  61  and the press roller  62 . 
     In exemplary embodiments, the pressure member  64  can be formed of a metal plate to easily transmit heat to the heating roller  61 . However, the present general inventive concept is not limited thereto. That is, in exemplary embodiments, the pressure member  64  can be formed of various other thermally conductive materials. In exemplary embodiments, temperature sensors  66  may be arranged on a surface of the pressure member  64 , as illustrated in  FIG. 4 . In the present exemplary embodiment, the pressure member  64  is formed of a stainless steel plate having a Teflon™ (e.g., polytetrafluoroethylene) coated on an outer surface thereof, and the plurality of temperature sensors  66  can be spaced apart from one another in the axial direction of the heating roller  61  on the surface of the pressure member  64 . Accordingly, the heater  61   a  in the heating roller  61  may be controlled based on a temperature measured by the temperature sensors  66 . 
     Although the present exemplary embodiment describes the pressure member  64  as extending by a length greater than a width of the printing medium P, to thereby realize a grinding effect of the pressure member  64  throughout a length of the heating roller  61 , the pressure member  64  may extend in the axial direction of the heating roller  61  so that the length of the pressure member  64  may be equal to or greater than that of the heating roller  61 . 
     In addition, although the present exemplary embodiment describes the pressure member  64  as being formed of a metal plate to easily transmit heat from the heating roller  61  to the temperature sensor  66 , the pressure member  64  may be made of an elastically deformable and highly polymerized material, such as polyimide, etc., if there is no temperature sensor  66  disposed on the pressure member  64 . 
       FIG. 5  illustrates a fusing unit  70  according to an exemplary embodiment of the present general inventive concept. 
     As illustrated in  FIG. 5 , a pair of pressure members  74  and a pair of supporting members  75  to support the pressure members  74  are circumferentially spaced apart from one another, so that the pair of pressure members  74  come into surface contact with two locations of an outer peripheral surface of a heating roller  71  to apply a face pressure to the heating roller  71 . In exemplary embodiments, pressing against the two locations of the outer peripheral surface of the heating roller  71  by using the pair of pressure members  74  may increase a grinding efficiency with respect to the outer peripheral surface A of the heating roller  71 . However, the present general inventive concept is not limited thereto. That is, in exemplary embodiments, the pressure members  74  may contact the outer peripheral surface A of the heating roller  71  at more than two locations. 
       FIG. 6  illustrates a fusing unit  80  according to an exemplary embodiment of the present general inventive concept.  FIG. 7  is a schematic view of a fusing unit  90  usable with an image forming apparatus according to an exemplary embodiment of the present general inventive concept. 
     The fusing unit  80  includes a heating roller  81 , having a heater  81   a  disposed therein, and a press roller  82  arranged opposite to each other within a fusing case  83 , a pressure member  84  to apply a face pressure to an outer peripheral surface A of the heating roller  81  so as to grind the outer peripheral surface A of the heating roller  81 , and a supporting member  85  to support the pressure member  84  to the fusing case  83 . 
     In exemplary embodiments, to prevent impurities, such as paper dust or developer from being trapped between the heating roller  81  and the pressure member  84 , the fusing unit  80  may further include a drive motor  88  to generate a rotation power, a drive roller  87  to be rotated by the drive motor  88 , and a loop-shaped belt  86 , one side of which is supported on the drive roller  87  and the other side of which is supported on the pressure member  84 . 
     In exemplary embodiments, the pressure member  84  can be formed of an elastically deformable plate and may be bent to have an arc-shaped cross section. This shape has the effect of assisting the belt  86  to easily move along an outer surface of the pressure member  84 . A bent region of the pressure member  84  can be supported on the outer peripheral surface A of the heating roller  81  with the belt  86  interposed therebetween, to thereby apply a face pressure onto the outer peripheral surface A of the heating roller  81 . Also, both distal ends  84   a  of the bent pressure member  84  can be supported respectively on the supporting member  85 , so that the pressure member  84  may be kept bent via the supporting members  85 . 
     In exemplary embodiments, the drive roller  87  can be periodically rotated by the drive motor  88 , such that the belt  86  continuously moves a section of the belt  86  arranged between the heating roller  81  and the pressure member  84 . Accordingly, even if impurities are trapped between the heating roller  81  and the pressure member  84 , the impurities may be rapidly released from between the heating roller  81  and the pressure member  84  via a movement of the belt  86 . 
     Although the exemplary embodiment illustrated in  FIG. 6  describes the pressure member  84  as being formed of an arcuately bent plate, in the exemplary embodiment illustrated in  FIG. 7 , a pressure member  94  may take the form of a rod having a circular cross section, and a belt  96  can be wound on the pressure member  94 . Accordingly, the pressure member  94  may act to apply a face pressure to an outer peripheral surface A of a heating roller  91  via the belt  96  interposed therebetween. 
     Although the exemplary embodiments illustrated in  FIGS. 6 and 7  illustrate the belts  86  and  96  as being interposed between the heating rollers  81  and  91  and the pressure members  84  and  94 , the belts  86  and  96  may serve as additional elements to prevent developer from being trapped between the heating rollers  81  and  91  and the pressure members  84  and  94 . Therefore, in alternative exemplary embodiments, the pressure members  84  and  94  may come into direct contact with the outer peripheral surfaces A of the heating rollers  81  and  91  to thereby apply a face pressure to the heating rollers  81  and  91 , without using the belts  86  and  96 . 
     In addition, although the above described exemplary embodiments describe the pressure members  64 ,  74 , and  84  as being formed of an elastically deformable material, this is devised to allow the pressure members  64 ,  74 ,  84  to more easily apply a face pressure onto the heating roller  61 ,  71 ,  81  by coming into surface contact with the outer peripheral surface A of the heating roller  61 ,  71 ,  81 . Therefore, in exemplary embodiments, the pressure member  64 ,  74 ,  84  may be made of a non-elastic deformable material, similar to the rod-shaped pressure member  94 . However, the present general inventive concept is not limited thereto. That is, in exemplary embodiments, the pressure member  64 ,  74 ,  84  may be formed in various shapes to provide an elastic force onto an outer peripheral surface of the heating roller  61 ,  71 , and  81  to thereby remove impurities, such as developer, from the outer peripheral surface A of the heating roller  61 ,  71 , and  81 . 
       FIG. 8  illustrates a fusing unit  200  according to an exemplary embodiment of the present general inventive concept. 
     The fusing unit  200  includes a heating roller  210 , having a heater  210   a  disposed therein, and a press roller  220  arranged opposite to each other within a fusing case  230 , a pressure member  240  coupled to the fusing case  230  via a support member  250 . In exemplary embodiments, the distal ends  240   a  of the pressure member  240  are coupled to the support member such that a portion of the pressure member  240  applies an elastic force against an outer peripheral surface A of the heating roller  210  to thereby maintain a desired surface roughness of the heating roller  210 . The pressure member  240  may be formed in an arc-shape which contacts the outer peripheral surface A of the heating roller  210 . 
       FIG. 9  illustrates a fusing unit  300  according to an exemplary embodiment of the present general inventive concept. 
     The fusing unit  300  includes substantially similar components of the exemplary embodiment illustrated in  FIG. 8 , except for a pressure member  340  which is formed of an elastic material such that distal ends  340   a  thereof contact two locations of an outer peripheral surface A of the heating roller  210 . That is, the pressure member  340  may be integrally formed from a single piece of material such that the distal ends  340   a  form arcs which contact the outer peripheral surface A of the heating roller  210 . The pressure member  340  is coupled to the fusing case  230  such that the distal ends  340   a  provide a constant force against two portions of the outer peripheral surface A of the heating roller  210  while the heater roller  210  is rotated in a forward or reverse direction. The distal ends  340   a  may be spaced apart from the outer peripheral surface A of the heating roller  210  to prevent causing damage to the heater roller  210 . 
     As apparent from the above description, according to the exemplary embodiments of the present general inventive concept, a pressure member applies a face pressure to an outer surface of a heating roller, to cause grinding of the outer surface of the heating roller. This has the effect of reducing and/or preventing an increase in surface roughness of the heating roller despite being used for a long period of time and consequently, minimizing and/or preventing a deterioration in an image quality of the image forming apparatus. 
     Although some exemplary embodiments of the present general inventive concept have been illustrated and described, it would be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined in the claims and their equivalents.