Patent Publication Number: US-6665504-B2

Title: Fusing device of electrophotographic image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2001-60143, filed Sep. 27, 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 relates to a fusing device of an electrophotographic image forming apparatus, and more particularly, to a fusing device of an electrophotographic image forming apparatus having a fusing roller and end caps securing an electric connection between a heater supplying heat to the fusing roller and a power supply device coupled to the heater. 
     2. Description of the Related Art 
     FIG. 1 is a schematic perspective view of a conventional electrophotographic image forming apparatus. Referring to FIG. 1, the conventional electrophotographic image forming apparatus includes a paper ejecting unit  1 , an operating unit  2 , a control board cover  3 , an upper cover opening button  4 , a paper display window  5 , a multi-purpose feeding window  6 , a paper cassette  7 , an option cassette  8 , and an auxiliary stand  9 . 
     FIG. 2 is a schematic cross-sectional view of a fusing device  10  of a conventional electrophotographic image forming apparatus employing a halogen lamp as a heat source. 
     Referring to FIG. 2, the conventional fusing device  10  includes a cylindrical fusing roller  11  and a heater  12 , e.g., the halogen lamp, installed in an interior center portion of the fusing roller  11 . 
     A coating layer  11   a,  such as Teflon, is coated on a surface of the fusing roller  11 . The heater  12  generates heat from an interior portion of the fusing roller  11 , and the fusing roller  11  is heated by a radiant heat emitted from the heater  12 . 
     FIG. 3 is a longitudinal cross-sectional view illustrating a relationship between the fusing roller and a pressure roller of the conventional electrophotographic image forming apparatus employing the halogen lamp as the heat source as shown in FIG.  2 . 
     Referring to FIG. 3, a pressure roller  13  is disposed to face a sheet of paper  14  at a lower portion of the fusing device  10 . The pressure roller  13  is elastically supported by a spring  13   a  to press the paper  14  passing between the fusing roller  11  and the pressure roller  13  with a predetermined pressure. A powdered toner image  14   a  is formed on the paper  14  and is pressed with a predetermined pressure and heated by heat when the paper  14  passes between the fusing roller  11  and the pressure roller  13 . In other words, the toner image  14   a  is fused and fixed on the paper  14  by the heat of the fusing roller  11  and pressure of the pressure roller  13 . 
     A thermistor  15  measuring a surface temperature of the fusing roller  11  and a thermostat  16  cutting off a power supply of the heater from an external power source when the surface temperature of the fusing roller  11  exceeds a predetermined set value, are provided at one side of the fusing roller  11 . The thermistor  15  measures the surface temperature of the fusing roller  11  and transmits an electric signal corresponding to the measured temperature to a controller (not shown) of a printer (not shown). The controller controls a quantity of electricity supplied to the halogen lamp  12  according to the measured temperature to maintain the surface temperature of the fusing roller  11  within a given range. When the surface temperature of the fusing roller  11  exceeds the predetermined set value because the thermistor  15  and the controller fails in controlling the surface temperature of the fusing roller  11 , a contact (not shown) of the thermostat  16  becomes open to cut off the power supply of the halogen lamp  12  from the external power source. 
     The conventional fusing device  10  using the halogen lamp  12  as the heat source unnecessarily consumes a large amount of electric power. Particularly, when power is turned on, the conventional fusing device  10  requires quite a long warming-up time. The warming-up time may range from several tens of seconds to several minutes. In addition, in the conventional fusing device  10 , since the fusing roller  11  is heated by radiation emitted from the heat source  12 , heat transmission is slow, and compensation for a temperature deviation caused by a decrease in temperature occurring due to a contact with the paper  14  is slow. As a result, it is difficult to maintain the surface temperature of the fusing roller  11  constant. Moreover, since the electric power must be periodically supplied to the heat source  12  in order to maintain the surface temperature of the fusing roller  11  constant in a standby mode in which an operation of the printer is in pause, unnecessary electric power is consumed. A considerable time is required to convert the standby mode into an operation mode for an image output, thereby making it difficult to achieve a fast image output. 
     FIG. 4 is a cross-sectional view of another conventional fusing device  200  employed in the electrophotographic image forming apparatus. 
     Referring to FIG. 4, a heating plate  22  is provided at the inner bottom portion of a flexible, cylindrical film tube  21 . A pressure roller  23  is disposed to face the heating plate  22 , and the paper  14  is disposed therebetween. 
     The film tube  21  is rotated by a separate rotating device. Locally heating a portion of the heating tube  21  disposed between the heating plate  22  and the pressure roller  23  consumes a low power, but this method is difficult to be applied to fast printing. 
     In order to solve the above problem, fusing devices adopting a heat pipe capable of instantaneously heating the fusing devices by a high heat conductivity and having a low power consumption characteristic are disclosed in Japanese Patent publication Nos. Hei 6-348176, Hei 11-282294 and 2000-25976. 
     In the fusing devices adopting the heat pipe, a heat source is arranged at one portion of a fusing roller, the portion deviating from a fusion area. If the heat source is arranged in such a manner, an overall size of the fusing device may increase. Thus, it is necessary to solve another problem of a structural complexity. 
     Fusing devices having a heat source incorporated into a fusing roller as disclosed in Japanese Patent publication Nos. Showa 60-55368, Hei 4-335691, Hei 4-360185, Hei 8-171301, Hei 8-262905, Hei 8-305195 and Hei 9-90811, do not encounter an increased structural complexity. However, since these fusing devices have a plurality of heat pipes locally disposed in the fusing roller, a manufacturing process becomes very complex. Also, since the heat pipes are locally disposed in the fusing roller, there is a temperature difference between portions among adjacent heat pipes and portions contacting the heat pipes. 
     According to a method in which a heat-generating resistive coil is inserted into the heat pipe, power supply portions disposed at both ends of the heat-generating resistive coil are electrically and thermally weak. 
     In particular, since insulating caps at both ends of the fusing roller are complex in view of shape and structure, an insulation of the insulating caps ensuring durability thereof is difficult to achieve. In addition, due to limitations of a heat-generating resistive element used in the fusing device in view of a voltage withstanding characteristic and a voltage application range, special materials should be used, causing a high manufacture cost. 
     SUMMARY OF THE INVENTION 
     To solve the above and other problems, it is an object of the present invention to provide a fusing device of an electrophotographic image forming apparatus with improved end caps establishing a stable electrical connection between a power supply and a heater. 
     Additional objects and advantageous 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. 
     To achieve the object of the present invention, there is provided a fusing device of an electrophotographic image forming apparatus. The fusing device includes a tubular internal pipe sealed at its ends to maintain a predetermined internal pressure to accommodate a predetermined amount of a working fluid in its inner space, a heater installed to wrap the internal pipe to generate heat, a power supply unit electrically connected to the heater to supply an external power to the heater, a cylindrical roller installed to wrap the heater, and end caps installed at both ends of the cylindrical roller, wherein each end cap includes a large-diameter portion in which an electrode electrically connected to the power supply unit is to be installed, and a small-diameter portion fittingly fixed to the end of the cylindrical roller by a locking unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become more 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 perspective view illustrating an outer appearance of a conventional electrophotographic image forming apparatus; 
     FIG. 2 is a cross-sectional view of a fusing device having a halogen lamp as a heat source in the conventional electrophotographic image forming apparatus of FIG. 1; 
     FIG. 3 is a cross-sectional view illustrating a relationship between the fusing device and a pressure roller of the conventional electrophotographic image forming apparatus shown in FIG. 2; 
     FIG. 4 is another cross-sectional view of the conventional fusing device employed in the electrophotographic image forming apparatus; 
     FIG. 5 is a cross-sectional view of a fusing device according to an embodiment of the present invention; 
     FIG. 6 is a cross-sectional view of a fusing roller of the fusing device shown in FIG. 5; 
     FIG. 7A is an exploded perspective view illustrating an end cap and a cylindrical roller in the fusing device of FIG. 5; 
     FIG. 7B is a perspective view illustrating the end cap shown in FIG. 7A; 
     FIG. 7C is a perspective view illustrating a power transmission end cap of the fusing device of FIG. 5; 
     FIG. 8A is an exploded perspective view illustrating an end cap and a cylindrical roller according to another embodiment of the present invention; 
     FIG. 8B is a perspective view illustrating the end cap shown in FIG. 8A; 
     FIG. 9 is an exploded perspective view illustrating the end cap and the cylindrical roller according to another embodiment of the present invention; 
     FIG. 10 is an exploded perspective view illustrating the end cap and the cylindrical roller according to another embodiment of the present invention; 
     FIG. 11 is an exploded perspective view illustrating the end cap and the cylindrical roller according to another embodiment of the present invention; 
     FIG. 12 is an exploded perspective view illustrating the end cap and the cylindrical roller according to another embodiment of the present invention; and 
     FIG. 13 is an exploded perspective view illustrating the end cap and the cylindrical roller 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 in order to explain the present invention by referring to the figures. 
     FIG. 5 is a cross-sectional view of a fusing (fixing) device  200  according to an embodiment of the present invention, and FIG. 6 is a cross-sectional view of a fusing roller  210  of the fusing device  200  shown in FIG.  5 . 
     Referring to FIGS. 5 and 6, a fusing device  200  includes a fusing roller  210  which rotates in a direction in which a sheet of print paper  250  having a toner image  251  thereon is ejected, i.e., in a direction indicated by an arrow A, and a pressure roller  220  which is installed to face the fusing roller  210  through the print paper  250  therebetween and rotates in a direction indicated by an arrow B to be in contact with the fusing roller  210 . 
     The fusing roller  210  includes a cylindrical roller  212 , a protective layer  211  coated on the cylindrical roller  212  with Teflon, a heater  213  installed inside the cylindrical roller  212  to generate heat when receiving electricity from a power supply unit  300 , and an internal pipe  214  which is installed inside the heater  213  and is sealed at its ends to maintain a predetermined internal pressure. 
     An insulating layer  216   a  is formed between an outer surface of the internal pipe  214  and the heater  213 , and another insulating layer  216   b  is formed between an inner surface of the cylindrical roller  212  and the heater  213 . The heater  213  is installed to wrap the inner pipe  214 . In this embodiment of the present invention, the heater  213  is a resistive heat-generating coil. 
     A predetermined fraction of a volume of the inner pipe  214  is filled with a working fluid  215 . Also, a power supply unit  300 , which is connected to an external power supply supplying the electricity to the heater  213 , is installed in a frame  400  disposed adjacent to both ends of the fusing roller  210 . 
     A thermistor  230  is mounted on a top of the fusing roller  210  to be in contact with the protective layer  211  to measure a surface temperature of the fusing roller  210 . A thermostat  240  is also installed around the fusing roller  210  to cut off the power (electricity) supply from the power supply unit  300  when the surface temperature of the fusing roller  210  suddenly rises. 
     An end cap  217  and a power transmission end cap  218  are installed at both ends of the fusing roller  210 . 
     FIG. 7A is an exploded perspective view illustrating the end cap  217  and the cylindrical roller  212 , FIG. 7B is a perspective view illustrating the end cap  217  shown in FIG. 7A, and FIG. 7C is a perspective view illustrating a power transmission end cap of the fusing device  200  of FIG.  5 . 
     Referring to FIGS. 7A and 7B, the end cap  217  includes a large-diameter portion  217   a  and a small-diameter portion  217   b.    
     An electrode  310  is electrically connected to the power supply unit  300  to supply the electricity to the heater  213  and inserted into the large-diameter portion  217   a  to contact a lead  213   a  of the heater  213  when the end cap  217  is coupled to the end cap  217  as shown in FIG.  6 . 
     The electrode  310  is connected to the end cap  217  using a fastening unit. In this embodiment, the electrode  310  is connected to the end cap  217  using a mechanical fastening unit such as a bolt or screw. 
     The small-diameter portion  217   b  is connected to the cylindrical roller  212 , and a hole  217   c  is formed at one side of an interior thereof so that the lead  213   a  of the heater  213  is inserted into the hole  217   c  to be connected to the electrode  310 . A diameter t1 of the small-diameter portion  217   b  is equal to or slightly greater than an internal diameter t2 of the cylindrical roller  212  to be forcibly fitted into the cylindrical roller  212 . 
     In a state in which the small-diameter portion  217   b  is not properly fitted into the cylindrical roller  212 , if the fusing roller  210  is repeatedly rotated for a long time, a fitted portion of the cylindrical roller  212  and the small-diameter portion  217   b  becomes loose. Then, the end cap  217  moves relative to the fusing roller  210  so that the electrode  310  and the lead  213   a  are disconnected from each other. Thus, it is necessary to perfectly fix the small-diameter portion  217   b  onto the fusing roller  210 . 
     To this end, a locking unit is provided on an outer surface of the small-diameter portion  217   b.  The locking unit is configured such that a plurality of convex portions  260  are symmetrically formed on the outer surface of the small-diameter portion  217   b,  and a plurality of concave portions  270  corresponding to the convex portions  260  are formed on an inner surface of the cylindrical roller  212 . 
     Thus, if the small-diameter portion  217   b  is fitted into the cylindrical roller  212 , the convex portions  260  are engaged with corresponding ones of the concave portions  270 . As the end cap  217  is forcibly fitted into the fusing roller  210 , a relative movement between the cylindrical roller  212  and the end cap  217  is suppressed (prevented) by a tight engagement between the convex portions  260  and the concave portions  270 , thereby avoiding a disconnection between the electrode  310  and the lead  213   a  of the heater  213 . 
     Referring to FIG. 7C, the power transmission end cap  218  is the same as the end cap  217  in view of configuration. However, a gear  219  is formed on an outer surface of the large-diameter portion  218   a,  and the gear  219  is rotated by a gear of a driving unit (not shown). Thus, the fusing roller  210  is rotated together with the electrode  310 . 
     FIG. 8A is an exploded perspective view illustrating the end cap  217  and the cylindrical roller  212  according to another embodiment of the present invention, and FIG. 8B is a perspective view illustrating the end cap  217  shown in FIG.  8 A. 
     Referring to FIGS. 8A and 8B, the end cap  217  is the same as that shown in FIGS. 7A through 7C, except that a plurality of protrusions  261  are further provided on the outer surface of the small-diameter portion  217   b,  and a plurality of recesses  271  are further provided on the inner surface of the cylindrical roller  212 . 
     Since the protrusions  261  are tapered, if the small-diameter portion  217   b  is fitted into the cylindrical roller  212 , the protrusions  261  are engaged with the recesses  271 , thereby fixing the end cap  217  to the cylindrical roller  212  without the relative movement. 
     FIG. 9 is an exploded perspective view illustrating the end cap  217  and the cylindrical roller  212  according to another embodiment of the present invention. 
     Referring to FIG. 9, as the locking unit, a male screw portion  262  parallel to an axis T of the cylindrical roller  212  is formed on the outer surface of the small-diameter portion  217   b,  and a female screw portion  272  corresponding to the male screw portion  262  and parallel to the axis T of the cylindrical roller  212  is formed on the inner surface of the cylindrical roller  212 . 
     FIG. 10 is an exploded perspective view illustrating the end cap and a cylindrical roller according to another embodiment of the present invention. 
     Referring to FIG. 10, the end cap  217  is the same as that shown in FIG. 9 in view of configuration, except that as the locking unit, a plurality of protrusions  263  are further provided on the outer surface of the small-diameter portion  217   b,  and a plurality of recesses  273  corresponding to the protrusions  263  are further provided on the inner surface of the cylindrical roller  212 . 
     FIG. 11 is an exploded perspective view illustrating the end cap  217  and the cylindrical roller  212  according to another embodiment of the present invention. 
     Referring to FIG. 11, as the locking unit, a plurality of tapered protrusions  264  are formed on the outer surface of the small-diameter portion  217   b,  and a plurality of recesses  274  corresponding to the protrusions  264  are formed on the inner surface of the cylindrical roller  212 . 
     Since the protrusions  264  are tapered, when the end cap  217  is connected to the cylindrical roller  212 , the small-diameter portion  217   b  is smoothly inserted into the cylindrical roller  212 , and when a perfect insertion is established, the protrusions  264  are engaged with the recesses  274 , thereby securely fixing the end cap  217  to the cylindrical roller  212  and simultaneously providing a torque to the cylindrical roller  212  during a rotation of the fusing roller  210 . 
     FIG. 12 is an exploded perspective view illustrating the end cap  217  and the cylindrical roller  212  according to another embodiment of the present invention. 
     Referring to FIG. 12, as the locking unit, a plurality of convex portions  265  are formed on the outer surface of the small-diameter portion  217   b  so as to slant at a predetermined angle with respect to the axis T of the cylindrical roller  212 , and a plurality of concave portions  275  corresponding to the convex portions  265  are formed on the inner surface of the cylindrical roller  212 . 
     The convex portions  265  may be formed so as to be slanted rightward or leftward with respect to the axis T of the cylindrical roller  212 . The above-described configuration provides a connection force for connecting the end cap  217  to the cylindrical roller  212  and provides torque to the cylindrical roller  212  during the rotation of the fusing roller  210 . A shape of the convex portions  265  may be a square or a rectangular or may have a predetermined curvature. 
     FIG. 13 is an exploded perspective view illustrating the end cap  217  and the cylindrical roller  212  according to another embodiment of the present invention. 
     Referring to FIG. 13, as the locking unit, a male screw  266  is formed on the outer surface of the small-diameter portion  217   b,  and a female screw  276  corresponding to the male screw  266  is formed on the inner surface of the cylindrical roller  212 . 
     Thus, the end cap  217  is connected to the cylindrical roller  212  by rotatably inserting the mal screw  266  into the female screw  276  according to a screw direction. The screw direction can be selected as rightward or leftward in consideration of a rotation direction of the fusing roller  210 . 
     As described above, the fusing device of the electrophotographic image forming apparatus according to the present invention has the end caps at both ends of the fusing roller securely supplying the electricity from the power supply unit to the heater supplying heat to the fusing roller, thereby providing a maximized durability and operating safety to the fusing roller. 
     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 sprit of the invention, the scope of which is defined in the claims and their equivalents.