Abstract:
A fusing device of an electrophotographic image forming apparatus. The fusing device includes a fusing roller that is heated to be a predetermined temperature, and a pressing roller that presses a sheet of paper passing between the fusing roller and the pressing roller toward the fusing roller. In addition, the fusing roller includes a cylindrical roller having a predetermined diameter, a heater positioned inside the cylindrical roller to heat the cylindrical roller, a rubber member that is formed on a center portion of an outer circumference on the cylindrical roller, and heat resistance portion that is formed on both end portions of the cylindrical roller.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority of Korean Patent Application No. 2003-96199, filed on Dec. 24, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a fusing device of an electrophotographic image forming apparatus, and, more particularly, to a structure of end portions of a fusing roller.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, in an electrophotographic color image forming apparatus such as a color laser printer, a predetermined electrostatic latent image is formed on a photosensitive body, and the electrostatic latent image is developed with a toner, and the developed resultant is transferred onto a sheet of paper after passing through a predetermined transfer medium. In addition, the resultant that is transferred on the sheet of paper is heated and pressed to be permanently fused thereon.  
         [0006]     Referring to  FIG. 1 , the conventional electrophotographic color image forming apparatus includes a photosensitive drum  10 , a charger  11  that charges the photosensitive drum  10 , a laser scanning unit  12  that is a light scanning unit to form a predetermined electrostatic latent image on the charged photosensitive drum  10  by scanning the light, a developing unit  13  that develops the electrostatic latent image with toners of four colors, that is, yellow (Y), magenta (M), cyan (C), and black (K) colors, a transfer belt  14  that sequentially overlaps the images of four colors formed on the photosensitive drum  10 , a first transfer roller  14   a  that transfers the four color images that is developed on the photosensitive drum  10  onto the transfer belt  14 , a second transfer roller  14   b  that transfers the four color images on the transfer belt  14  onto the sheet of paper, and a fusing device  15  that heats and presses the sheet of paper to permanently fuse the transferred image on the sheet of paper.  
         [0007]     Reference numeral  16  denotes a paper cassette, reference numeral  17  denotes a blade to clean the photosensitive drum, reference numeral  18  denotes an eraser, and reference numeral  19  denotes a conveying path through which the sheet of paper may be discharged.  
         [0008]     The fusing device  15  heats the sheet of paper, on which the toner images are transferred to melt the toner image in a powder state and to fuse the image on the sheet of paper. The fusing device  15  includes a fusing roller that fuses the toner on the sheet of paper, and a pressing roller that pushes the sheet of paper toward the fusing roller.  
         [0009]     The fusing roller is formed as a cylindrical roller made of metal, such as stainless steel, that has a rubber member formed on a circumference thereof. The metal cylindrical roller allows a temperature of the fusing roller to be substantially uniform, and the rubber member softly contacts the sheet of paper that passes between the pressing roller and the fusing roller.  
         [0010]     The fusing roller is a rotating body and has a structure that allows an electrical connection to a heating element to be included therein.  
         [0011]     U.S. Pat. No. 6,628,917 discloses a fusing roller, both sides of which are attached by end caps. The end cap is a resin such as polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), or a nylon that is filled with a filler, such as glass fiber, having a low thermal conductivity at a high temperature.  
         [0012]     When a surface temperature of the fusing roller is high, the temperature of the cylindrical roller is higher than the surface temperature of the fusing roller, and the end cap may melt.  
         [0013]     On the other hand, Japanese Laid-open Patent No. H10-3223 discloses a fusing roller that has bearings installed on both end portions thereof, and a gear is installed on one end portion of the fusing roller. Here, an adiabatic member is used between the fusing roller and the bearing.  
       SUMMARY OF THE INVENTION  
       [0014]     Therefore, the present invention provides a fusing device of an electrophotographic image forming apparatus. The fusing device has an improved end structure so as to prevent a rotating member from being damaged by heat transmission occurring on both ends of the fusing roller.  
         [0015]     According to an aspect of the present invention, the fusing device includes a fusing roller that is heated to a predetermined temperature, and a pressing roller that presses a sheet of paper passing between the fusing roller and the pressing roller toward the fusing roller. The fusing roller includes a cylindrical roller having a predetermined diameter, a heater positioned inside the cylindrical roller to heat the cylindrical roller, a rubber member that is formed on a center portion of an outer circumference on the cylindrical roller, and heat a resistance portion that is formed on both end portions of the cylindrical roller.  
         [0016]     According to other aspects of the present invention, the heat resistance portion may comprise at least one or more holes formed on each of the end portions of the cylindrical roller. The hole may be formed to be long in a perpendicular direction with respect to a rotary shaft direction of the cylindrical roller. The hole may be filled with a resin, including ceramic filler. The heat resistance portion may include at least one or more grooves that are formed on both ends of the cylindrical roller, and the grooves are filled with the resin, including ceramic filler. Lastly, the recess may be formed to be long in a perpendicular direction with respect to a shaft direction of the cylindrical roller.  
         [0017]     Additional and/or other 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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0019]      FIG. 1  is a schematic view illustrating a conventional electrophotographic color image forming apparatus;  
         [0020]      FIG. 2  is a schematic cross-sectional view illustrating a fusing device of an electrophotographic image forming apparatus according to the present invention;  
         [0021]      FIG. 3  is a longitudinal cross-sectional view illustrating the fusing roller shown in  FIG. 2 ;  
         [0022]      FIGS. 4   a  and  4   b  are perspective views illustrating a first end cap of  FIG. 3 ;  
         [0023]      FIGS. 5   a  and  5   b  are perspective views illustrating a second end cap of  FIG. 3 ;  
         [0024]      FIG. 6  is a cross-sectional view illustrating an end portion of the fusing roller, at which an embodiment of heat resistance portion is formed;  
         [0025]      FIG. 7  is a plan view illustrating a circumferential surface of the end portion of the fusing roller shown in  FIG. 6 ;  
         [0026]      FIG. 8  is a cross-sectional view illustrating an end portion of the fusing roller, at which another embodiment of the heat resistance portion is formed; and  
         [0027]      FIG. 9  is a cross-sectional view illustrating an end portion of the fusing roller, at which still another embodiment of the heat resistance portion is formed. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Reference will now be made in detail to the 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 to explain the present invention by referring to the figures.  
         [0029]      FIG. 2  is a schematic cross-sectional view illustrating a fusing device of an electrophotographic image forming apparatus according to the present invention, and  FIG. 3  is a longitudinal cross-sectional view illustrating a fusing roller shown in  FIG. 2 .  
         [0030]     Referring to  FIGS. 2 and 3 , the fusing device  100  includes a fusing roller  110  having a cylindrical roller  113  that rotates in a direction of an arrow A, which corresponds to a discharging direction of a sheet of paper  150  on which a toner image  151  is formed. The fusing device  100  further includes a pressing roller  160  that faces the fusing roller  110  the sheet of paper  150  interposed therebetween. The pressing roller  160  rotates in a direction of an arrow B while pressing the sheet of paper  150  toward the fusing roller  110 .  
         [0031]     As illustrated in  FIG. 3 , the cylindrical roller  113  includes a cylinder portion  113   a  and stepped portions  113   b  and  113   c  on both end portions of the cylinder portion  113   a . A silicon rubber layer  112  having a substantially 1.5 mm thickness is formed on a surface of the cylinder portion  113   a , and a toner release layer  111  that is made of teflon to be about 20˜30 μm thick is formed on the silicon rubber layer  112 . A heat generator  114  is disposed inside the cylindrical roller  113 . Meanwhile, a heat pipe  115 , both end portions of which are sealed so as to maintain a predetermined pressure therein, is disposed inside the heat generator  114 . According to various embodiments of the invention, the thickness of the silicon rubber layer  112  may be varied according to surface material used in the pressing roller  160 .  
         [0032]     Swaging the end portion of the cylinder to form the step inward forms the stepped portion  113   b  that is connected to an end portion of the cylinder portion  113   a . Accordingly, the stepped portion  113   b  and the cylinder portion  113   a  are formed integrally with each other. The stepped portion  113   c  that is connected to the other end portion of the cylinder portion  113   a  is coupled to the cylinder portion  113   a  via a screw combination. That is, a female screw is formed on the end portion of the cylinder portion  113   a , and a male screw corresponding to the female screw is formed on the stepped portion  113   c . In another embodiment of the invention, the screw combination may be reversed. In the above structure, in which one end portion of the cylindrical roller  113  may be opened, the heat pipe  115  and the heat generator  114  having larger diameters than those of the stepped portions  113   b  and  113   c  are put into the cylindrical roller  113 , and a pressure substantially equal to 100˜150 times atmospheric_pressure is pressed into the inner portion of the heat pipe  115  to expand the heat pipe  115 . Then the heat generator  114  may be closely adhered to an outer circumferential surface of the heat pipe  115  and an inner circumferential surface of the fusing roller  113 . Thereafter, the stepped portion  113   c  may be coupled to the corresponding end portion of the cylinder portion  113   a  by a screwing motion. On the other hand, ball bearings  129  are installed on the stepped portions  113   b  and  113   c  to support the fusing roller  110  that includes the stepped portions  113   b  and  113   c.    
         [0033]     The heat generator  114  includes a Ni—Cr resistance coil  114   a  that generates heat via externally supplied electricity, a set of magnesium oxide (MgO) layers  114   b  and  114   c  that surround the resistance coil  114   a , and lead wires  117  that apply electricity to both ends of the resistance coil  114   a  of the heat generator  114 . A Cr—Fe wire may be used as the resistance coil  114   a.    
         [0034]     The heat pipe  115  is a pipe having end portions sealed. A predetermined amount of working fluid  116  is contained in the heat pipe  115 . The working fluid  116  functions as a heat medium that is vaporized by the heat generated by the heat generator  114  to transmit the heat to the cylindrical roller  113 , prevent the temperature variation on the surface of the cylindrical roller  113 , and heat the entire cylindrical roller  113  rapidly.  
         [0035]     The temperature on the surface of the silicon rubber layer  112  that directly contacts the sheet of paper  150 , on which the toner image is transferred, through the toner release layer  111  should be maintained at approximately 175° C. However, the temperature on the inner surface of the silicon rubber layer  112 , which contacts the cylindrical roller  113 , may rise to 230˜240° C. Thus, silicon material that is durable against such high temperatures is used.  
         [0036]     The cylindrical roller  113  is heated by the heat generated by the heat generator  114  or evaporation heat of the working fluid  116  that is contained in the heat pipe  115 , and transmits the heat to the silicon rubber layer  112  to melt the toner  151  of powder state formed on the sheet of paper  150 . The cylindrical roller  113  is made of stainless steel, aluminum (Al), or copper (Cu).  
         [0037]     A first end cap  120  and a second end cap  130  are inserted into the both sides of the fusing roller  110 . The second end cap  130  has a substantially similar structure to that of the first end cap  120 . However a difference between the two features is that, in the second end cap  130  a gear is formed along the outer circumferential surface of the second end cap  130  and rotates by engaging with a gear of a motor.  
         [0038]      FIGS. 4   a  and  4   b  are perspective views of the first end cap  120  shown in  FIG. 3 , and  FIGS. 5   a  and  5   b  are perspective views of the second end cap  130  shown in  FIG. 3 .  
         [0039]     Referring to  FIGS. 4   a  and  5   b , lead holes  122  and  132 , through which the leads (refer to  117  of  FIG. 3 ) that are connected to the both ends of the resistance coil  113   a  pass, are formed on the first end cap  120  and the second end cap  130 . Protrusion keys  124  and  134  are formed on circumferential portions of the end caps  120  and  130 . The protrusion keys  124  and  134  are engaged with key recesses (not shown) formed inside of the stepped portions  113   b  and  113   c . Concave portions  125  and  135 , into which end portions of the heat pipe  115  are partially inserted, are formed at inner center portions of the end caps  120  and  130  that face both of the ends of the heat pipe  115 . Electrode recesses  126  and  136 , into which electrodes  121  are inserted, are formed on outer center portions of the end caps  120  and  130 . That is, the electrode recesses  126  and  136  are found on the opposite side of the concave portions  125  and  135 . The electrodes  121  supply the electricity to the lead  117  that is inserted into the lead holes  122  and  132  and bent at a right angle.  
         [0040]     The end caps  120  and  130  may be fabricated using a resin such as a polyphenylene sulfide (PPS), a polybutylene terephthalate (PBT), and a nylon that is filled with a filler such as glass fibers. The glass fiber filled nylon may be advantageous because this material is less transformed by heat of a high temperature environment.  
         [0041]     On the other hand, the fusing device of the present invention includes a heat resistance portion to thermally protect the end caps  120  and  130  and the bearings  129 .  
         [0042]      FIG. 6  is a cross-sectional view illustrating an end portion of the fusing device, on which an embodiment of the heat resistance portion is formed, and  FIG. 7  is a plan view spreading the circumferential surface of the end portion of the fusing roller shown in  FIG. 6 .  
         [0043]     Referring to  FIGS. 6 and 7 , a plurality of holes (h) are formed on both ends of the fusing roller. The holes h are formed to be long in a perpendicular direction with respect to a direction of a rotary shaft denoted by an arrow R. The holes h reduce the amount of heat transmitted from the center portion of the cylindrical roller to the end caps  120  and  130  and the bearings  129 .  
         [0044]     Heat capacity is represented by following equation 1.  
               Q   cond     =       -   k     ⁢           ⁢   A   ⁢       ⅆ   T       ⅆ   x                 (   1   )             
 
 where Q cond  denotes thermal conductive quantity, T denotes a temperature of the cylindrical roller, k denotes a thermal conductivity of the cylindrical roller material, A is a heat transfer area (end portion of the cylindrical roller), and x denotes a distance of a heat conductive portion. 
 
         [0045]     According to equation 1, a plurality of holes h formed on the end portions of the cylindrical roller  113  reduce the conduction heat from the cylindrical roller  113  to the heat conducted portion, for example, the bearings  129  or the end caps  120  and  130 .  
         [0046]     In  FIG. 6 , since the holes h are formed to be long in a perpendicular direction with respect to the heat conducting direction, the conduction heat may be reduced by increasing by decreasing the heat transfer area, that is, A in equation 1.  
         [0047]      FIG. 8  is a cross-sectional view illustrating an end portion of the fusing roller, at which another embodiment of the heat resistance portion is formed.  
         [0048]     Referring to  FIG. 8 , a plurality of holes h are formed on both end portions of the fusing roller. The holes h are filled with the resin (c) that includes a ceramic filler having low heat conductivity than that of the cylindrical roller  113 , such as an alumina. As discussed above, the PPS, PBT, or the nylon may be used as the resin since the advantages of these materials as used in the previously mentioned embodiments have similar effects here.  
         [0049]     The material filled in the holes h reduces the quantity of heat that is transmitted from the center portion of the cylindrical roller to the end caps  120  and  130  and the bearings  129 .  
         [0050]      FIG. 9  is a cross-sectional view illustrating an end portion of the fusing device, at which still another embodiment of the heat resistance portion is formed.  
         [0051]     Referring to  FIG. 9 , grooves (g) are formed on both end portions of the cylindrical roller, and the grooves are filled with the resin (c) including a material having lower heat conductivity than that of the cylindrical roller  113 , for example, the ceramic filler such as alumina. The material filled in the grooves g reduces the quantity of heat transferred from the center portion of the cylindrical roller  113  to the end caps  120  and  130  and the bearings  129 .  
         [0052]     As is described above, since the fusing roller of the electrophotographic image forming apparatus according to the present invention includes the heat resistance portion on both ends of the fusing roller to reduce quantity of the heat transmitted from the fusing roller to the bearings and end caps, transformation of the bearing or the end cap due to the heat can be prevented.  
         [0053]     Although a few 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 these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.