Abstract:
Fusing equipment of an image forming apparatus, includes: a fusing roller fixing a toner image on a printer paper and comprising a supporting layer formed at an inner portion of the fusing roller, a separating layer formed at an outermost portion of the fusing roller, an a heating layer formed between the supporting layer and the separating layer to supply heat; a thermistor detecting a temperature of the fusing roller to control the heating layer; and a pressing roller pressing the printing paper against an end of the fusing roller during a rotational movement of the fusing roller while being in contact with the fusing roller.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2002-37459, filed Jun. 29, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an image forming apparatus, and more particularly, to fusing equipment of an electro-photographic image forming apparatus for fixing an image transferred thereto onto a paper. 
   2. Description of the Related Art 
   Generally, an electro-photographic image forming apparatus has a photosensitive drum that receives digital image signals from a laser scanning unit (LSU) and forms an electrostatic latent image accordingly, a developing unit that develops the electrostatic latent image of the photosensitive drum with a developing agent (hereinafter called ‘toner’), and a transfer unit that transfers the developed image formed on the photosensitive drum onto a recording paper. 
   The transfer unit includes fusing equipment. The fusing equipment fixes the toner onto a printing medium with heat and pressure. 
     FIG. 1  shows conventional fusing equipment for use in an image forming apparatus. As shown in  FIG. 1 , the conventional fusing equipment includes a fusing roller  80  formed on an upper portion of the fusing equipment, a pressing roller  96  formed on a lower portion of the fusing equipment, and a thermistor  82  that detects a surface temperature of the fusing roller  80 . 
   The fusing roller  80  includes a heating lamp  86  formed in a center portion of the fusing roller  80 , an air layer  88  surrounding the heating lamp  86 , a supporting layer  90  supporting the fusing roller  80 , a resilient layer  92  formed of resilient material and surrounding the supporting layer  90 , and a separating layer  94  surrounding the resilient layer  92 . A halogen lamp is usually used as the heating lamp  86 . 
   The pressing roller  96  rotates while being in contact with the separating layer  94  with an intervention of printing paper  99  therebetween. The pressing roller  96  is forced upward against the fusing roller  80  by a compression spring  98 . 
   The thermistor  82  is in contact with the surface of the fusing roller  80 , and detects the temperature of the rotating fusing roller  80 . The fusing roller  80  fixes toner  95  on the printing paper  99  when the printing paper passes between the fusing roller  80  and the pressing roller  96 . 
   In the conventional fusing equipment, radiation heat generated from the heating lamp  86  is transmitted to the supporting layer  90  via the air layer  88  and then transmitted through the resilient layer  92  to the separating layer  94 , thereby transmitting the radiation heat to the printing paper  99 . 
   At room temperature, a sufficient amount of heat is not quickly transmitted to the surface of the fusing roller  80  to melt the toner  95 . Although there are differences in a melting point (temperature) of respective toner types of the toner  95  and a structure of the fusing equipment, it generally takes a longer period of time to warm up the fusing roller  80 . When power is just turned on or when the printer is in a sleep state, it takes from about 30 seconds to about 1 minute for a mono laser beam printer (LBP), or from about 3 minutes to about 5 minutes for a color laser beam printer (CLBP) to be in a standby state, i.e., to be warmed-up for printing. 
   The printer enters into the sleep state to save energy consumption when there is no printing command for a long time. In the sleep state, the power to a heat source of the fusing roller  80  is cut off, thereby maintaining a fusing roller temperature at the room temperature. Then the printer enters into a standby state to be supplied with the printing paper. In the standby state, the fusing roller temperature is maintained at a lowest level that can be increased to a printing temperature allowing the printing at a maximum speed. 
   As mentioned above, it takes a lengthy time for the conventional fusing equipment to be warmed-up because it usually employs the halogen lamp as the heat source and is constructed in such a manner that the heating lamp  86  is heated inside of the supporting layer  90  of the fusing roller  80  to heat up the fusing roller  80  through the air layer  88 . 
   Further, even though the supporting layer  90  is heated by the heat source, it takes a considerable time that the heat reaches the separating layer  94  disposed at the outer most side of the fusing roller  80  because the resilient layer  92 , which surrounds the supporting layer  90 , is made of materials of a low heat conductivity, such as a rubber. 
   Meanwhile, because the thermistor  82  is formed on an outside of the fusing roller  82  and is in contact with the surface of the separating layer  94 , the thermistor  82  can be attached with foreign substances, such as dirt and dust. As a result, especially when it is used for a long time, the thermistor  82  would detect the surface temperature of the fusing roller inaccurately. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide fusing equipment of an image forming apparatus which is warmed up within a short period of time as a fusing roller of the fusing equipment is heated directly by a heat source. 
   Another aspect of the present invention is to provide a fusing roller of an image forming apparatus, capable of supplying sufficient heat to a surface of the fusing roller even in a printing operation at high speed. 
   Yet another aspect of the present invention is to provide a fusing roller of an image forming apparatus which has an improved heating efficiency. 
   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. 
   The above and/or other aspects of the presenting invention are accomplished by providing fusing equipment of an image forming apparatus including a fusing roller and a pressing unit. The fusing roller comprises a supporting layer formed in an inner portion of the fusing roller, a separating layer formed on an outermost portion of the fusing roller, and a heating layer formed between the supporting layer and the separating layer to supply heat. The fusing equipment comprises a thermistor detecting a temperature of the fusing roller. The pressing unit presses a printing paper toward a lower end of the fusing roller during a rotational movement of the fusing roller while being in contact with the fusing roller. 
   The pressing unit can have the same construction as the fusing roller, whereby a pressing roller can serve a function of heating as well as pressing the printing paper. 
   The thermistor can be mounted in an inside of the fusing roller. 
   The supporting layer may be formed of a pipe which is made of a metallic material, such as aluminum or iron. 
   The heating layer includes a hot wire wound around an outer circumference of the supporting layer, an insulating member formed between the supporting layer and the hot wire, and an insulation resilient layer filled (disposed) in a first gap between windings of the hot wire created after the winding of the hot wire, and also filled (disposed) in a second gap between the hot wire and the separating layer. The insulation resilient layer has resiliency and insularity. 
   The hot wire is made of a material with a predetermined electric resistance, such as a tungsten or nichrom wire, and the insulation resilient layer is made of a material having a property of a silicone or a rubber that has an electric insularity, heat resistance and resiliency. Further, the insulation resilient layer can be formed of a material with high heat resistance, such as ceramics or mica. 
   The separating layer is coated with a material with a non-sticky property, such as polytetrafluoroethylene (TEFLON®, DUPONT), or is enclosed by a polytetrafluoroethylene (TEFLON®, DUPONT) tube. 
   According to another aspect of the present invention, fusing equipment of an image forming apparatus includes a fusing roller that has a supporting layer formed at an inner portion, a heating layer formed at an inside of the supporting layer to supply heat, a separating layer formed at an outermost portion, and a resilient layer formed between the supporting layer and the separating layer; a thermistor detecting a temperature of the fusing roller; and a pressing unit pressing a printing paper against a lower end of the fusing roller during a rotational movement of the fusing roller while being in contact with the fusing roller. 
   The heating layer includes a hot wire winding around an inner circumferential surface of the supporting layer and an insulating member having a heat resistance and charged (disposed) between windings of the hot wire and between the hot wire and the supporting layer. 
   The supporting layer may comprise a pipe made of a metallic material, such as aluminum or iron, and the hot wire is made of a material with a predetermined electric resistance, such as a tungsten wire or a nichrom wire. 
   The resilient layer is made of a material having a property of either a silicone or a rubber, and the separating layer is coated with a material of a non-sticky property, such as polytetrafluoroethylene (TEFLON®, DUPONT), or is enclosed by a polytetrafluoroethylene (TEFLON®, DUPONT) tube. 
   According to another aspect of the present invention, instead of a conventional indirect heating method by which a heating source, such as a halogen lamp, radiates heat through the air, a direct heating method is used. Accordingly, the supporting layer and the separating layer both disposed in an inside of the fusing roller can be intervened by the heating layer, or the heating layer can be formed to be in direct contact with an inner surface of the supporting layer to directly heat a surface of the fusing roller. As the image forming apparatus can reach a print fusing temperature within a short period of time, a warm-up time is shortened, and a given image is printed out rapidly. Further, a sufficient amount of heat can be supplied to the fusing roller even in a printing operation at high speed, and a heating efficiency of the fusing roller is improved. 
   Further, by forming the thermistor in the inside of the fusing roller, the thermistor can be kept free from foreign substances, such as dust, and as a result, inaccurate temperature detection of the thermistor can be prevented. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and 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  is a cross-sectional view showing conventional fusing equipment of an image forming apparatus; 
       FIG. 2  is a cross-sectional view showing a direct heating type of fusing equipment in an image forming apparatus according to an embodiment of the present invention; 
       FIG. 3  is a longitudinal cross-sectional view showing an internal structure of the fusing equipment of  FIG. 2 ; 
       FIG. 4  is a cross-sectional view showing fusing equipment according to another embodiment of the present invention; 
       FIG. 5  is a cross-sectional view showing fusing equipment according to another embodiment of the present invention; and 
       FIG. 6  is a cross-sectional view showing fusing equipment according to another embodiment of the present invention. 
   

   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 in order to explain the present invention by referring to the figures. 
   Hereinafter, the embodiments of the present invention will be described in greater detail with reference to the accompanying drawings. 
     FIGS. 2 and 3  are cross-sectional views showing fusing equipment according to an embodiment of the present invention. As shown in  FIGS. 2 and 3 , the fusing equipment includes a fusing roller  10  formed at an upper portion of the fusing equipment, a pressing roller  22  formed at a lower portion of the fusing equipment, and a thermistor  21  that defects a surface temperature of the fusing roller  10 . The pressing roller  22  is urged upward against the fusing roller  10  by a compression spring  24 . The fusing roller  10  fixes toner  28  on printing paper  26  when the printing paper passes between the fusing roller  10  and the pressing roller  22 . 
   The fusing roller  10  has a center portion  11 , a supporting layer  12  surrounding the center portion  11 , a separating layer  20  defining an outer-most surface of the fusing roller  10 , and a heating layer  13  formed between the supporting layer  12  and the separating layer  20 . The supporting layer  12  supports the fusing roller  10 . 
   The heating layer  13  includes a hot wire  16  wound around an outer circumference of the supporting layer  12 , an insulating material  14  formed between the supporting layer  12  and the hot wire  16 , and an insulating resilient layer  18  disposed in a first gap between windings of the hot wire created after the winding of the hot wire, and also disposed in a second gap between the hot wire  16  and the separating layer  20 . The first gap and the second gap are filled with the insulating resilient layer  18 . 
   Taking a heat efficiency and a lifespan of the hot wire  16  into account, the hot wire  16  is formed of materials with a predetermined electric resistance, i.e., a tungsten wire, a nichrom wire, etc. For a better resiliency of the fusing roller  10 , the insulating resilient layer  18  is made of silicone or materials having a rubber property with a high electric insulation, a heat resistance, and a resiliency. If there is no requirement for the resiliency, the insulating resilient layer  18  is made of materials with a high heat and electric insulation, such as ceramics, mica, etc. 
   The separating layer  20  is coated with polytetrafluoroethylene (TEFLON®, DUPONT) that has an excellent non-sticky property, or is enclosed by a polytetrafluoroethylene (TEFLON®, DUPONT) tube. The supporting layer  12  comprises a pipe of a metallic material, such as aluminum (Al) or iron (Fe), to provide a mechanical strength to the supporting layer  12 . The supporting layer  12  stores the heat generated from the heating layer  13  therein and transmits the stored heat to the separating layer  20  together with the heat from the heating layer  13 . 
   By forming the heating layer  13  between the supporting layer  12  and the separating layer  13 , the heating layer  13  directly heats the outer-most layer of the fusing roller  10 , i.e., the separating layer  20 . As a result, a warm-up time of the image forming apparatus is shortened, and a sufficient amount of the heat is transmitted to the surface of the fusing roller  10 , thereby increasing the heating efficiency of the fusing equipment. 
     FIG. 4  is a cross-sectional view showing fusing equipment according to another embodiment of the present invention. As shown in  FIG. 4 , a basic structure of the fusing equipment is similar to that of the fusing equipment shown in  FIGS. 2 and 3 . Accordingly, the like elements will be given the same reference numerals throughout, and description thereof will be omitted. According to this embodiment of the present invention, the fusing equipment is provided with a thermistor  21   a  which is inserted in the heating layer  13  to detect the surface temperature of the fusing roller  10 . 
   During rotating together with the fusing roller  10 , the thermistor  21   a  is disposed in the insulation resilient layer  18  of the heating layer  13  and contacts with the separating layer  20  to thereby detect the surface temperature of the separating layer  20 . 
   By constructing the fusing equipment as described above, the thermistor  21   a  can remain free from foreign substances, such as dust, for a long period of time. 
     FIG. 5  is a cross-sectional view showing fusing equipment according to another embodiment of the present invention. As shown in  FIG. 5 , the fusing equipment is provided with the pressing roller  23  and the fusing roller  10 , both of which are constructed in the same way. Further, the thermistor  21   a  is inserted in the heating layer  20 . The other basic structures are the same as the fusing equipment shown in  FIGS. 2 through 4 . 
   By constructing the fusing roller  10  and the pressing roller  23  in the same structure, a heat transmission can be made through a direct pressure from upper and lower rollers, such as the fusing roller  10  and the pressing roller  23 , to the printing paper. As shown in  FIG. 5 , the fusing equipment in a sleep state can reach the print fusing temperature within a shortest time and also supply a sufficient amount of heat even during a printing operation at a high speed. 
     FIG. 6  is a cross-sectional view showing fusing equipment according to another embodiment of the present invention. The fusing equipment, like as in the first, second and third embodiments, includes a fusing roller  30  having a center portion  40 , a thermistor  42  and a pressing roller  44 . 
   As shown in  FIG. 6 , the fusing roller  30  includes a supporting layer  34 , a hot wire  32  wound around an inner surface (circumference) of the supporting layer  34 , an insulation material  31  disposed in a first gap formed between windings of the hot wire  32  created after the winding of the hot wire  32 , and also disposed in a second gap formed between the hot wire  32  and the inner circumference of the supporting layer  34 . Further, a resilient layer  36  is formed between the supporting layer  34  and the separating layer  38  to provide a resiliency to the fusing roller  30 . The thermistor  42  is in contact with a surface of the separating layer  38  from an outside of the fusing roller  30 . The pressing roller  44  is urged upward against the fusing roller  30  by a compression spring  46 . 
   The supporting layer  34  comprises a pipe made of a metallic material, such as aluminum (Al) or iron (Fe). The hot wire  32  is formed of materials with a proper electric resistance, such as a tungsten or nichrom wire. The separating layer  38  is coated with polytetrafluoroethylene (TEFLON®, DUPONT) or is enclosed by a polytetrafluoroethylene (TEFLON®, DUPONT) tube. 
   Although the preferred embodiments of the present invention have been described, it will be understood by those skilled in the art that the present invention should not be limited to the described preferred embodiments, but various changes and modifications can be made within the spirit and scope of the present invention as defined by the appended claims and their equivalents.