Patent Publication Number: US-6909870-B2

Title: Fixing apparatus for a printer having a paper separating unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2002-43279, filed on Jul. 23, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fixing apparatus for a printer, and more particularly, to a fixing apparatus for a printer, the fixing apparatus having a paper separating unit that can prevent elements from being worn and which can be manufactured at low cost. 
   2. Description of the Related Art 
     FIG. 1  is a cross-sectional view of a conventional fixing apparatus for a printer having a paper separating unit and a paper ejecting apparatus. Referring to  FIG. 1 , the conventional fixing apparatus includes a heating roller  11 , a pressing roller  13 , a paper separating unit  15 , and a tension spring  17 . The heating roller  11  fixes an image on paper S by heating the paper S on which the image developed by a conventional developing unit (not shown) is formed. The pressing roller  13  helps to fix the image by pressing the paper S that contacts the heating roller  11  and which is inserted in an interface with the heating roller  11 . The paper separating unit  15  contacts the heating roller  11  and separates the paper S. The tension spring  17  applies an elastic force to the paper separating unit  15  and maintains the paper separating unit  15  in a correct position. 
   The image on the paper S passes through the fixing apparatus, is fixed on the paper S, and is then moved to the paper ejecting apparatus via a paper ejecting guide  25 . The paper ejecting apparatus ejects the paper S, which is supplied while first and second ejecting rollers  21  and  23  rotate in contact with each other, to the outside. 
     FIG. 2  is an enlarged view of portion A of FIG.  1  and shows a contact surface between the paper separating unit  15  installed in the conventional fixing apparatus for a printer and the heating roller  11 . Preferably, the conventional paper separating unit  15  should form a sharp end, to contact the heating roller  11  closely and to separate the paper. However, in general, the conventional paper separating unit  15  is formed of plastics having a blunt end, as shown in FIG.  2 . In such a case, while the paper separating unit  15  operates, the surface of the heating roller  11  is damaged by the blunt end of the paper separating unit  15 , causing image quality to deteriorate. 
   Also, since the heating roller  11  of the conventional paper separating unit  15  operates at a temperature of about 180 C, the paper separating unit  15  is formed of a material resistant to heat even at a high temperature In addition, TEFLON® is coated on the surface of the paper separating unit  15 . As a result, the manufacturing cost of the paper separating unit  15  is greatly increased. 
   SUMMARY OF THE INVENTION 
   The present invention provides a fixing apparatus for a printer, the fixing apparatus having a low-cost paper separating unit which can effectively separate paper without damaging the surface of a heating roller. 
   Additional aspects and advantages of the invention 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 invention. 
   According to an aspect of the present invention, a fixing apparatus for a printer includes a heating unit which fixes an image on a paper by heating the paper passing through a developing unit, a pressing unit which contacts the heating unit, presses the paper passing through an interface with the heating unit and helps to fix the image on the paper, and a paper separating unit which includes a separation member. The separation member has a sharp end contacting the heating unit to separate the paper, an arm member having one end to which the separation member is attached and pivots, centering on a hinge shaft at a predetermined angle, and an elastic member which is connected to the other end of the arm member and applies an elastic force so that the arm member is maintained in a correct position. The separation member may be a leaf spring formed of a SUS-family material (SUS is the Japanese Industrial Standard grade of stainless steel) that is strongly resistant to heat, and TEFLON® may be coated on the surface of the separation member. A polyimide film may also be attached to the surface of the separation member. 
   The arm member is formed of a press type material forming a predetermined angle, and the separation member is attached to one end of the arm member. The elastic member is connected to the other end of the arm member, and the hinge shaft extends from the center of the arm member such that the arm member pivots, centering on the hinge shaft at a predetermined angle. 
   The heating unit is a heating roller. The pressing unit may be a pressing roller or a transfer roller. 
   The present invention provides a paper separating unit for a fixing apparatus for a printer that can prevent paper from being rolled in a direction of a heating roller and which is formed using a low-cost material, such that sheets of paper are effectively separated from the heating roller, damage to the heating roller is prevented, and a deterioration of the printing quality is prevented. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  schematically shows a conventional printer; 
       FIG. 2  is an enlarged cross-sectional view of portion A of  FIG. 1 ; 
       FIG. 3A  is a perspective view of a fixing apparatus for a printer, according to an embodiment of the present invention; 
       FIG. 3B  is a cross-sectional view of the fixing apparatus for a printer, according to an embodiment of the present invention; 
       FIG. 4A  is an exploded view of a paper separating unit employed in the fixing apparatus for a printer, according to the embodiment of the present invention; 
       FIG. 4B  is an enlarged cross-sectional view of portion B of  FIG. 4A ; 
       FIG. 5  shows a drum-shaped printer using the fixing apparatus according to an embodiment of the present invention; and 
       FIG. 6  shows a belt-shaped printer using the fixing apparatus according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiments of the present invention, 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 invention by referring to the figures. 
   Hereinafter, the present invention will be described in detail by describing a preferred embodiment of the invention with reference to the accompanying drawings. 
     FIG. 3A  is a perspective view of a fixing apparatus for a printer, according to an embodiment of the present invention. Referring to  FIG. 3A , a separation member  32  in which a sharp end extends to contact a heating roller  31  is coupled with one end of an arm member  34 , and a hinge shaft  36  that extends from the center of the arm member  34  is inserted in both fixing ends, which the hinge shaft  36  pivotably contacts, and a tension spring  37  is connected to the other end of the arm member  34  and applies an elastic force to the arm member  34 . A bar is inserted in a ring-shaped first ejecting roller  41  as part of a paper ejecting apparatus spaced apart from the fixing apparatus by a predetermined gap. The fixing apparatus and the paper ejecting apparatus are covered with an external housing  45 . 
     FIG. 3B  is a cross-sectional view of the fixing apparatus for a printer, according to an embodiment of the present invention. Referring to  FIG. 3B , the fixing apparatus to fix an image on paper S includes a heating roller  31 , a pressing roller  33 , and a paper separating unit  35 . The fixing apparatus fixes an image on the paper S, and then the paper S is ejected through a paper ejecting apparatus. 
   The heating roller  31  and the pressing roller  33  rotate in contact with each other. The heating roller  31  heats the paper S so that toner particles forming an image are completely absorbed to, and fixed on, the paper S. The pressing roller  33  helps to fix the image by heat, together with the heating roller  31 , by applying a pressure to the paper S. However, if the paper S is heated, the paper S can roll in a heating flux direction such that the paper S is rolled in the direction of the heating roller  31 . Thus, a paper separating unit  35  is necessary to separate the paper S rolled on the surface of the heating roller  31  from the heating roller  31 . Here, reference numerals  41  and  43  denote first and second ejecting rollers, respectively. 
     FIG. 4A  is an exploded view of a paper separating unit  35  employed in the fixing apparatus for a printer, according to an embodiment of the present invention. Referring to  FIGS. 3B and 4A , the paper separating unit  35  includes a separation member  32  which contacts the heating roller  31  and separates the paper S from the surface of the heating roller  31 , the arm member  34  formed to pivot at a predetermined angle by the hinge shaft  36 , and the elastic member  37  which applies an elastic force to the arm member  34  and applies a restoring force so that the arm member  34  is maintained in a correct position. 
   Referring to  FIG. 4B , the separation member  32  is formed by coating TEFLON® on a member formed of a press type material, for example, an SUS-family material. The separation member  32  makes the paper S separate easily by forming a sharp and extendable end. Also, the separation member  32  is formed of a high heat-resistant material and thus is not deformed by contact with the heating roller  31 . As shown in  FIG. 4A , a groove  38   b  to be engaged with a protrusion  38   a  is formed in a body part of the separation member  32  so that the separation member  32  is easily coupled with the arm member  34  in which the protrusion  38   a  is formed, attaching the separation member  32  to the arm member  34 . 
     FIG. 4B  is an enlarged cross-sectional view of portion B of  FIG. 4A , presenting an enlarged end of the separation member  32  of FIG.  4 A. As shown in  FIG. 4B , the paper separating unit  35  employed in the fixing apparatus for a printer, according to the embodiment of the present invention, unlike the conventional paper separating unit, forms a sharp and extendable end contacting the heating roller  31 , and thus makes the paper S separate more easily from the heating roller  31 . 
   The arm member  34  includes one end to which the separation member  32  is attached and the other end that extends from the one end at a predetermined angle. The arm member  34  pivots, centering on the hinge shaft  36  at a predetermined angle. The arm member  34  does not directly contact the heating roller  31 , and thus can be formed of general plastics. As such, manufacturing costs can be reduced compared to the conventional paper separating unit. 
   The elastic member  37  is a helicoidal spring, applies an elastic force to the other end of the arm member  34  to which the separation member  32  is not attached, and transfers the elastic force to the separation member  32  through the arm member  34  such that the separation member  32  continuously contacts the surface of the heating roller  31 . 
   The paper separating unit employed in the fixing apparatus for a printer, according to an embodiment of the present invention can prevent damage to elements due to their life spans, thus preventing a decrease in life spans of the elements and deterioration of the image quality. In addition, a high heat-resistant material used to form the paper separating unit is replaced with a press type material, thus reducing costs. 
     FIG. 5  shows a drum-shaped printer using the fixing apparatus according to an embodiment of the present invention. Referring to  FIG. 5 , the drum-shaped printer using the fixing apparatus includes a paper feeding cassette  101  on which paper S is stacked, a paper feeding unit  102  which sequentially supplies the stacked paper S, a charging and developing unit  103  which forms an image on the supplied paper S, a transfer unit  103   e  which transfers the image developed by the charging and developing unit  103  onto the paper S, a fixing unit  104  which fixes the transferred image on the paper S, and an ejecting unit  105  which ejects the fixed paper S to the outside. A paper ejecting tray  106  which receives the ejected paper S may be connected to the ejecting unit  105 . 
   Here, the charging and developing unit  103  includes a photosensitive drum  103   a , a charger  103   b  which increases a surface potential of the photosensitive drum  103   a  to a charge potential, a laser scanner  103   c  which decreases part of the surface potential of the photosensitive drum  103   a  to an exposure potential to form an electrostatic latent image, and a developer  103   d  which supplies toner increased to a development potential to the photosensitive drum  103   a  to develop the electrostatic latent image. The transfer unit  103   e  is placed on the surface of the photosensitive drum  103   a  and transfers the image developed on the photosensitive drum  103   a  onto the paper S. The charging and developing unit  103  further includes a cleaner  103   f , which eliminates toner remaining on the surface of the photosensitive drum  103   a  after a transfer step. 
   The fixing apparatus for a printer shown in  FIGS. 3A and 3B , according to an embodiment of the present invention is used as the fixing unit  104 . The structure and operation of the fixing unit  104  are the same as the above descriptions for  FIGS. 4A and 4B . 
     FIG. 6  shows a belt-shaped printer using the fixing apparatus according to an embodiment of the present invention. Referring to  FIG. 6 , the belt-shaped printer using the fixing apparatus includes a photosensitive belt  200 , a driving roller  208  which rotates and moves the photosensitive belt  200  on a given route, a backup roller  214 , and a tension roller  220 . A charger  202 , which increases a surface potential of the photosensitive belt  200  to a charge potential, is placed on the surface of the photosensitive belt  200 . A laser scanner  206 , which decreases part of the surface potential of the photosensitive belt  200  to an exposure potential to form an electrostatic latent image, is placed under the photosensitive belt  200 . A developer  204 , which increases a toner of a predetermined color mixed with liquid carrier to a development potential, attaches the toner to a region in which the electrostatic latent image is formed, by static electricity and develops an electrostatic latent image, and is placed at one side of the laser scanner  206 . The toner applied by the developer  204  is dried by a drying roller  210  and a heating roller  212  such that a toner image is formed in which only toner remains in the electrostatic latent image on the photosensitive belt  200 . The toner image is transferred onto the paper S by a transfer roller  216  opposite to the backup roller  214 , and the photosensitive belt  200  is placed between the backup roller  214  and the transfer roller  216 . The toner image transferred onto the paper S is heated and pressed by a pressing roller  218  parallel to the transfer roller  216  at a predetermined interval. 
   Here, a paper separating unit  35  is installed between the transfer roller  216  and the pressuring roller  218  and separates the paper S rolled in the direction of the heating roller  218  from the surface of the pressing roller  218 . The paper separating unit  35  of  FIGS. 4A and 4B  is used as the paper separating unit, and the structure and operation of the paper separating unit  35  are the same as described above. 
   A fixing apparatus for a printer according to an embodiment of the present invention employs a paper separating unit which contacts a heating roller and can effectively separate paper, thus preventing deterioration of printing quality and preventing damage to elements. Using the fixing apparatus for a printer according to the present invention, the life spans of the elements are prolonged, and the performance of a printer is improved. 
   As described above, in the fixing apparatus for a printer, according to the present invention, the paper separating unit that prevents damage to elements during a paper separation operation can be manufactured at low cost, prevents deterioration of image quality, provides a high quality image, and prolongs the life spans of elements, thus improving the performance of a printer. 
   Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is define in the claims and their equivalents.