Patent Publication Number: US-2005129434-A1

Title: Fusing roller apparatus of electro-photographic image forming apparatus, and a process of manufactuing a fusing roller apparatus

Description:
BACKGROUND OF THE INVENTION  
      This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2003-91176, filed on Dec. 15, 2003, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.  
      1. Field of the Invention  
      The present invention relates to an electro-photographic image forming apparatus, and more particularly, the present invention relates to a fusing roller apparatus, and a process of manufacturing thereof, of an electro-photographic image forming apparatus for applying heat and pressure to a toner image to fuse and fix the toner image to printing paper.  
      2. Description of the Related Art  
      In general, electro-photographic image forming apparatuses include a fusing roller apparatus that applies heat and pressure to a toner image transferred to a printing medium so as to fuse and fix the toner image to the printing medium.  
       FIG. 1  is a lateral schematic cross-sectional view of a fusing roller apparatus of a conventional electro-photographic image forming apparatus using a halogen lamp as a heat source, and  FIG. 2  is a longitudinal cross-sectional view for showing the relationship between the fusing roller apparatus and a pressure roller of the conventional electro-photographic image forming apparatus of  FIG. 1 .  
      Referring to  FIG. 1 , a fusing roller apparatus  10  includes a fusing roller  10  of pipe type and a heat generator  12  which is installed in the inner center of the fusing roller  11  and made of a halogen lamp. A coated layer  11   a  is formed of Teflon on the surface of the fusing roller  11 . The heat generator  12  generates radiant heat inside the fusing roller  11 , and the fusing roller  11  is heated by the radiant heat transmitted from the heat generator  12 .  
      Referring to  FIG. 2 , a pressure roller  13  is located below the fusing roller apparatus  10 , and printing paper  14  is interposed between the fusing roller apparatus  10  and the pressure roller  13 . The pressure roller  13  is elastically supported by a spring assembly  13   a  to press the printing paper  14  passing between the fusing roller apparatus  10  and the pressure roller  13  against the fusing roller apparatus  10  by a predetermined force.  
      As the printing paper  14  carries a toner image  14   a  in a powder form between the fusing roller apparatus  10  and the pressure roller  13 , the printing paper  14  is hot-pressed by the predetermined force. In other words, the toner image  14   a  is fused and fixed to the printing paper  14  by the heat and force from the fusing roller apparatus  10  and the pressure roller  13 .  
      A conventional fusing roller apparatus using a halogen lamp as a heat source unnecessarily consumes a large amount of power. Thus, in a standby mode where the operation of a printer is suspended, the conventional fusing roller apparatus must be powered down to lower a temperature. In particular, the conventional fusing roller apparatus requires considerably long warm-up time until it reaches a target fusing temperature after power is turned on for a printing operation.  
      The time from when power is applied to when the conventional fusing roller apparatus reaches the target fusing temperature is called First-Print-Out-Time (FPOT). The conventional fusing roller apparatus requires a FPOT from tens of seconds to tens of minutes.  
      In the conventional fusing roller apparatus, a fusing roller is heated by radiant heat from the heat source, which results in a slow heat transfer speed. In particular, compensation for temperature variations due to a drop in the temperature of the fusing roller caused by contact with printing paper is delayed, so that it is difficult to uniformly control the distribution of temperature along the axial length of the fusing roller.  
      Also, even in the standby mode where the operation of the printer is suspended, power must be periodically applied to the heat source to keep the temperature of the fusing roller constant, thereby causing unnecessary power consumption. Moreover, it takes a considerable amount of time to switch the fusing roller from its standby mode to an operation mode for image output, so that the resultant image cannot be rapidly printed.  
     SUMMARY OF THE INVENTION  
      The present invention provides a fusing roller apparatus of an electro-photographic image forming apparatus which consumes a small amount of current and power, increases a temperature of a fusing roller to a target fusing temperature within a short period of time, and has a good insulation characteristic.  
      According to an aspect of the present invention, there is provided a fusing roller apparatus, and a process of manufacturing thereof, of an electro-photographic image forming apparatus, the fusing roller apparatus including: a cylindrical internal pipe; a fusing unit which is installed to enclose the internal pipe; a heat generator which is installed between the fusing unit and the internal pipe to generate heat; and an insulating layer which includes a first insulating layer that is formed between the heat generator and the fusing unit and a second insulating layer that is formed between the heat generator and the internal pipe to be thicker than the first insulating layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is a lateral schematic cross-sectional view of a fusing roller apparatus of a conventional electro-photographic image forming apparatus using a halogen lamp as a heat source;  
       FIG. 2  is a longitudinal cross-sectional view for showing the relationship between the fusing roller apparatus and a pressure roller of the conventional electro-photographic image forming apparatus of  FIG. 1 ;  
       FIG. 3  is a longitudinal schematic cross-sectional view of a fusing roller apparatus of an electro-photographic image forming apparatus, according to an embodiment of the present invention;  
       FIG. 4  is a lateral schematic cross-sectional view of the fusing roller apparatus of the electro-photographic image forming apparatus of  FIG. 3 ; and  
       FIG. 5  is a magnified view of portion “C” of  FIG. 4 .  
      Throughout the drawings it should be understood that like reference numbers are used to depict like features and structures. 
    
    
     DETAILED DESCRIPTION OF THE EXAMPLARY EMBODIMENTS  
      Referring to  FIGS. 3 and 4 , a fusing roller apparatus  200  of an electro-photographic image forming apparatus, according to an embodiment of the present invention, applies heat and pressure to a toner image  251  to fuse and fix the toner image  251  to printing paper  250 . The fusing roller apparatus  200  includes a fusing roller  210  which is installed to rotate in a direction indicated by arrow “A” so as to apply heat to the toner image  251  and a pressure roller  220  which faces the fusing roller  210  to press the toner image  251  against the fusing roller  210 . Here, the printing paper  250  is transferred between the fusing roller  210  and the pressure roller  220 .  
      The fusing roller  210  includes a cylindrical fusing unit  212 , an internal pipe  214 , a heat generator  213 , and an insulating layer  216 . A protection layer  211 , which is coated with Teflon, is formed on the surface of the fusing unit  212 . The internal pipe  214  is installed inside the fusing unit  212  and has two ends that are opened. The heat generator  213  is installed between the fusing unit  212  and the internal pipe  214  to helically enclose the internal pipe  214  and is supplied with a current from an external power supply to generate heat. The insulating layer  216  encloses the heat generator  213  to insulate the fusing unit  212  from the internal pipe  214  so that during application of the current to the heat generator  213 , a leakage current does not flow and insulation breakdown does not occur.  
      The fusing unit  212  and the internal pipe  214  are heated by the heat transmitted from the heat generator  213  so as to fuse and fix the toner image  251  to the printing paper  250 . The fusing unit  212  and the internal pipe  214  may be formed of stainless steel, aluminum (Al), copper (Cu), or the like.  
      It is preferable that the heat generator  213  is formed of a resistive heating coil which is supplied with the current from the external power supply to generate heat and includes a lead  213  a which extends from both ends thereof so as to be supplied with the current from the external power supply.  
      The insulating layer  216  includes a first insulating layer  216   a  which is interposed between the fusing unit  212  and the heat generator  213  and a second insulating layer  216   b  which is interposed between the heat generator  213  and the internal pipe  214 .  
      It is preferable that the insulating layer  216  is formed of a magnesium oxide (MgO) sheet or a glass sheet. The heat generated by the heat generator  213  is transmitted to the fusing unit  212  through the first insulating layer  216   a  and to the internal pipe  214  through the second insulating layer  216   b.    
      The heat transmitted to the internal pipe  214  is not used to increase a temperature of the fusing unit  212 . Thus, instead of transmitting a smaller amount of heat to the internal pipe  214 , a larger amount of heat must be transmitted to the fusing unit  212  to reduce FPOT.  
      It is preferable that the second insulating layer  216   b  is thicker than the first insulating layer  216   a . Also, it is preferable that the first insulating layer  216   a  is formed of a twofold MgO sheet or a twofold glass sheet and the second insulating layer  216   b  is formed of a threefold MgO sheet or a threefold glass sheet.  
      Since the MgO sheet or the glass sheet has the thickness of less than 0.1 mm, it is preferable that the first insulating layer  216   a  has the thickness of less than 0.2 mm and the second insulating layer  216   b  has the thickness of less than 0.3 mm.  
      An insulating material used for the insulating layer  216  has withstand voltage and insulation breakdown characteristics. The withstand voltage characteristic indicates a property of withstanding predetermined external power. The withstand insulation breakdown chracteristic indicates that a leakage current flows not to be more than 10 mA at a maximum withstand voltage for a minute, and thus insulation breakdown does not occur.  
                       TABLE 1                       Number of       Withstand       Times   Manufacturing Specifications   Voltage (kV)                                            1   MgO (0.1t × 40 mm × 40 mm)   3.57       2   MgO (0.1t × 40 mm × 40 mm)   3.41       3   MgO (0.1t × 40 mm × 40 mm)   3.38       4   MgO (0.1t × 40 mm × 40 mm)   3.67       5   MgO (0.1t × 40 mm × 40 mm)   3.75       6   MgO (0.1t × 40 mm × 40 mm)   3.83       7   MgO (0.1t × 40 mm × 40 mm)   3.73       8   MgO (0.1t × 40 mm × 40 mm)   3.32       9   MgO (0.1t × 40 mm × 40 mm)   3.63       10   MgO (0.1t × 40 mm × 40 mm)   3.56                  
 
      Table 1 shows the results of a withstand voltage test which was performed in conditions that a voltage was applied to an MgO sheet having the thickness of 0.1 t. Since the MgO sheet withstood a minimum voltage of 3.32 kV and a maximum voltage of 3.83 kV, a rated withstand voltage was determined to be more than 3 kV. Thus, the MgO sheet was viewed as satisfying the withstand voltage characteristic.  
      Thereafter, the rated withstand voltage of 3 kV was applied to the MgO sheet to check whether a leakage current was generated for a minute. The leakage current of 5 mA was generated for a minute and insulation breakdown did not occur. As a result, the MgO sheet satisfied the withstand insulation breakdown characteristic.  
      An end cap  217  and a power transmission end cap  218  are installed at both ends of the fusing roller  210 , respectively. The power transmission end cap  218  has a similar structure to the end cap  217 . However, the power transmission end cap  218  includes a power transmission portion  218  a, such as gear, which is connected to a power transmission device (not shown) installed in a frame  400 , which supports the fusing roller  210 , so as to rotate the fusing roller  210 .  
      An air vent  219  is formed in the end cap  217  and allows air to flow from the outside into an inner space  230  of the fusing roller  210  after the end cap  217  is installed at the fusing roller  210  so as to maintain a pressure of the inner space  230  of the fusing roller  210  to an atmospheric pressure.  
      Although the internal pipe  214  is heated by the heat transmitted from the heat generator  213 , the inner space  230  is kept at the atmospheric pressure due to the flow of air from the outside into the inner space  230  via the air vent  219 . The air vent  219  may also be formed in the power transmission end cap  218  or may be formed in both the end cap  217  and the power transmission end cap  218 .  
      Electrodes  220  are installed at the end cap  217  and the power transmission end cap  218 , respectively, and electrically connected to the lead  213   a . The current supplied by the external power supply is transmitted to the heat generator  213  through a power supply  300 , the electrodes  220 , and the lead  213   a.    
      A thermostat  240  and a thermistor  270  are installed above the fusing roller  210 . The thermostat  240  prevents the fusing unit  212  from being overheated by cutting off power when the surface temperatures of the fusing unit  212  and the protection layer  211  sharply increase. The thermistor  270  senses the surface temperatures of the fusing unit  212  and the protection layer  211 .  
      A process of manufacturing the fusing roller  210  will now be explained.  
      The second insulating layer  216   b  is formed to enclose the outer surface of the internal pipe  214 . Next, the heat generator  213  is helically installed to enclose the second insulating layer  216   b . Thereafter, the first insulating layer  216   a  is formed to enclose the heat generator  213 .  
      The internal pipe  214  on which the heat generator  213 , the first insulating layer  216   a , and the second insulating layer  216   b  have been prepared is inserted into the fusing unit  212 , the outer surface of which is coated with Teflon.  
      Both ends of the internal pipe  214  are hermetically sealed by an expanding apparatus, and then a predetermined pressure is applied to the inner space  230  to expand the internal pipe  214 . Here, it is preferable that the predetermined pressure is more than an air pressure of 140 mb.  
      The internal pipe  214  is expanded, the fusing unit  212  remains circular, and the heat generator  213  and the insulating layer  216  are plastically deformed. As a result, the heat generator  213 , the internal pipe  214 , the first insulating layer  216   a , and the second insulating layer  216   b  adhere closely to the inner surface of the fusing unit  212 .  
      In other words, as shown in  FIG. 5 , since the heat generator  213  is formed of a resistive heating coil, a space between adjacent portions of the resistive heating coil is fully filled with the first and second insulating layers  216   a  and  216   b  when the internal pipe  214  is expanded.  
      However, when the predetermined pressure is less than the air pressure of 140 mb, the first and second insulating layers  216   a  and  216   b  do not fully fill the space between the adjacent portions of the resistive heating coil when the internal pipe  214  is expanded. An air gap is formed in the space between the adjacent portions of the resistive heating coil. The incomplete adhesion among the fusing unit  212 , the heat generator  213 , and the internal pipe  214  may result in forming an air gap. The air gap deteriorates heat transfer efficiency from the heat generator  213  to the fusing unit  212 , which causes an increase in FPOT.  
      As described above, a fusing roller apparatus of an electro-photographic image forming apparatus according to the present invention can use an insulator having high withstand voltage and insulation breakdown characteristics to minimum the thickness of an insulating layer. Also, the fusing roller apparatus can allow a larger amount of heat to be transmitted to a fusing unit, which results in reducing FPOT.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing ftom the spirit and scope of the present invention as defined by the following claims.