Abstract:
A fusing system includes: a fusing unit which comprises a fusing belt which rotates around outer surfaces of at least two rollers which are distanced from each other, and a pressing roller which presses a printing medium together with the fusing belts and fuses an image which is transferred to the printing medium; a heat source which receives power to generate heat, and is mounted inside at least one of the two rollers; a driving source which drives at least one of the two rollers; a sensing unit which senses a surface temperature of the fusing belt; and a control unit which controls the heat source and the driving source so that the fusing belt can be driven when the temperature of the fusing unit increases if a printing order is applied.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims all benefits accruing under 35 U.S.C. §119 from Korean Patent Application No. 2007-89160, filed on Sep. 3, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an image forming apparatus, and more particularly, to a fusing system and a control method thereof driving a fusing unit and preheating the fusing unit to a predetermined temperature in an image data processing time to improve a fusing process. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, an electro-photographic image forming apparatus, such as, a laser printer, a facsimile machine, a photo-copier and a multi-functional product, forms an electrostatic latent image on an photoreceptor charged to have a predetermined electric potential by means of exposing, develops with a predetermined toner, and transmits and fuses a toner image to a printable medium to print an image. A fusing unit is provided on a printing path of the image forming apparatus, to fuse a transferred toner image to the printable medium by means of heating and pressing. In addition, a fusing system is provided to control the fusing unit depending on a control signal applied from a control unit so as to perform a fusing process. 
         [0006]      FIG. 1  is a schematic view illustrating a fusing system of a typical image forming apparatus. As shown in  FIG. 1 , the fusing system includes a fusing unit  10 , a sensing unit  20  and a control unit  31 , and a power source  35 . 
         [0007]    The fusing unit  10  includes a fusing roller  13  containing a heater  11  therein, and a pressing roller  17  disposed to face the fusing roller  13  and elastically pressed toward the fusing roller  13  by means of an elastic member  15 . 
         [0008]    The fusing roller  13  includes a core  13   a  formed of metal, and an elastic layer  13   b  provided to a surface of the core  13   a.  Accordingly, the core  13   a  is heated by a radiant energy of the heater  11 , and the elastic layer  13   b  is heated by thermal conduction. If the printable medium  1  carrying a non fused toner image  3  is transported to the fusing unit  10  passing through a fusing nip N formed between the fusing roller  13  and the pressing roller  17  which rotate, the toner image  3  is heated and pressed to be fused on the printable medium  1 , thereby completing the fusing process. 
         [0009]    The sensing unit  20  includes a thermistor  21  for sensing a surface temperature of the fusing roller  13 , a thermostat  23  for blocking the power source  35  applied to the heater  11  if the surface temperature of the fusing roller  13  exceeds a predetermined critical temperature, and a power switching unit  25  arranged to turn ON/Off for supplying of the power source  35  to the heat  11  depending on a signal from the control unit  31 . The thermistor  21  senses the surface temperature of the fusing roller  13 , and transmits the sensed result to the control unit  31 . The control unit  31  compares the sensed temperature with a predetermined critical temperature to control the power supplying to the heater  11  through the power switching unit  25 , so that the surface temperature of the fusing roller  13  can maintain a fusing temperature. 
         [0010]      FIG. 2  is a flowchart illustrating a temperature control method of the fusing system shown in  FIG. 1 . As shown in  FIG. 1  and  FIG. 2 , in the fusing system, if power is applied to the image forming apparatus, the control unit  31  heats the fusing roller  13  so that the surface temperature of the fusing roller  13  can increases up to a printing standby temperature, that is, preheats the fusing roller  13  at block Si. Then, the surface temperature of the fusing roller  13  maintains the printing standby temperature to stand by for a printing order until the printing operation is performed at block S 3 . Here, the printing operation indicates supplying of the printable medium, developing, transferring and fusing processes which are performed after the image forming apparatus receives the printing order from a host computer, and printing data is completely down loaded. 
         [0011]    Then, whether the printing operation is performed or not is determined at block S 5 . If the printing operation is not performed, the printing standby state is maintained until the printing operation is performed at block S 5 . On the other hand, if the printing operation is performed, the fusing roller  13  is heated so that the surface temperature of the fusing roller  13  can become the fusing temperature of approximately 180° C. to 190° C. which is higher than the printing standby temperature at block S 7 . Here, if the printing standby temperature is determined to be close to the fusing temperature, a temperature increasing time can be reduced during the fusing process. However, during the printing standby state, the printing medium is not supplied and the fusing unit  10  is not driven. As a result, the fusing roller  13  and the pressing roller  17  are apt to be deformed by heat and a fire danger due to overheating increases if the printing standby temperature is raised. Accordingly, there is a limit in raising the printing standby temperature to be more than approximately 140° C. 
         [0012]    Then, the printable medium  1  formed with the non fused toner image  3  passes between the fusing roller  13  and the pressing roller  17  to perform the fusing process at block S 9 . 
         [0013]    In the fusing system shown in  FIG. 1  and  FIG. 2 , the elastic layer  13   b  is formed of material having a low thermal conduction to prevent a surface temperature of the elastic layer  13   b  from largely varying although the heater  11  is repeatedly turned ON/OFF during fusing. In this case, a lot of time is required so that the surface temperature of the elastic layer  13   b  increases from the printing standby temperature to the fusing temperature by means of the heat supplied from the heater  11 . Accordingly, time to print a first page of the printable medium increases. 
         [0014]    In addition to the fusing system shown in  FIG. 1 , there is another fusing unit using a fusing belt configuration. Such a fusing unit includes a heating roller distanced from a fusing roller and containing a heater therein, and a fusing belt rotating around outer surfaces of the fusing roller and the heating roller. Here, a part of the fusing belt contacting to the heating roller is partially heated. Also, the heated part is expanded to the total surface of the fusing belt by means of rotation of the fusing belt in fusing so that the fusing nip can maintain the fusing temperature. 
         [0015]    In a preheating process of the belt type fusing unit, the heater heats the heating roller under the state that the fusing belt is stopped. Accordingly, a part of the fusing belt contacting with the heating roller or positioned adjacently thereto is capable of maintaining the preheating temperature by means of the thermal conduction, but the other parts thereof have a temperature lower than the preheating temperature. 
         [0016]    Accordingly, in an initial printing after a substantial time elapses in the printing standby state, the partially heated part of the fusing belt applies a predetermined amount of heat to the printable medium to maintain a fusing ability. However, the other parts having the low temperature have an insufficient amount of heat, thereby causing an inferior fusing process. 
       SUMMARY OF THE INVENTION 
       [0017]    Several aspects and example embodiments of the present invention provide a fusing system and a control method thereof driving and preheating a fusing unit before a printing operation is performed after a printing order to maintain a preliminary fusing temperature which is higher than a printing standby temperature and lower than a fusing temperature, thereby reducing a temperature increasing time up to the fusing temperature, and avoiding an inferior fusing when printing a first page of a printable medium. 
         [0018]    Additional aspects and/or 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 present invention. 
         [0019]    In accordance with an example embodiment of the present invention, a fusing system comprise: a fusing unit which comprises a fusing belt which rotates around outer surfaces of at least two rollers which are distanced from each other, and a pressing roller which presses a printing medium together with the fusing belts and fuses an image which is transferred to the printing medium; a heat source which receives power to generate heat, and is mounted inside at least one of the two rollers; a driving source which drives at least one of the two rollers; a sensing unit which senses a surface temperature of the fusing belt; and a control unit which controls the heat source and the driving source so that the fusing belt can be driven when the temperature of the fusing unit increases if a printing order is applied. 
         [0020]    According to an aspect of the present invention, the control unit may control the heat source and the driving source based on the temperature of the fusing unit which is sensed by the sensing unit, and a printing proceeding state. 
         [0021]    According to another aspect of the present invention, the control unit may control the temperature of the fusing unit to maintain a preliminary fusing temperature T 2  which is higher than a printing standby temperature T 1 , and lower than a fusing temperature T 3  during an image data processing time before a printing operation is started after the printing order is applied. 
         [0022]    According to an aspect of the present invention, the printing standby temperature T 1  may be the temperature of the fusing unit by means of preheating in a printing standby state, and the fusing temperature T 3  is the temperature of the fusing unit during the printing operation. 
         [0023]    According to an aspect of the present invention, the control unit respectively may turn ON/OFF the heat source and the driving source so that the heat source and the driving source can be respectively driven by a predetermined time unit during the image data processing time. 
         [0024]    In accordance with another example embodiment of the present invention, a fusing system comprises: a fusing unit which forms a fusing nip by means of a pressing force, and heats and presses a printing medium which passes through the fusing nip to fuse an image which is transferred to the printing medium; a heat source which receives power to generate heat, and supplies the heat to the fusing unit; a driving source which drives the fusing unit; a sensing unit which senses the temperature of the fusing unit; and a control unit which controls the heat source and the driving source based on the temperature of the fusing unit which is sensed by the sensing unit, and a printing proceeding state, wherein the control unit controls the temperature of the fusing unit so as to maintain a preliminary fusing temperature T 2  which is higher than a printing standby temperature T 1 , and lower than a fusing temperature T 3  during an image data processing time before a printing operation is started after a printing order is applied. 
         [0025]    According to an aspect of the present invention, the printing standby temperature T 1  may be the temperature of the fusing unit by means of preheating in a printing standby state, and the fusing temperature T 3  is the temperature of the fusing unit during the printing operation. 
         [0026]    According to an aspect of the present invention, the control unit may turn ON/OFF the heat source so that the heat source can be driven by a predetermined time unit during the image data processing time. 
         [0027]    According to another aspect of the present invention, the control unit may turn ON/OFF the driving source so that the driving source can be driven by a predetermined time unit during the image data processing time. 
         [0028]    According to an aspect of the present invention, the fusing unit may comprise: a fusing roller which is driven by means of the driving source, a heating roller which is distanced from the fusing roller, and contains the heat source therein, a fusing belt which rotates around outer surfaces of the fusing roller and the heating roller, and a pressing roller which is elastically biased toward the fusing roller to press the printing medium together with the fusing roller and the fusing belt. 
         [0029]    According to an aspect of the present invention, the fusing unit may comprise: a fusing roller which is driven by means of the driving source, and contains the heat source therein, and a pressing roller which is elastically biased toward the fusing roller to press the printing medium together with the fusing roller. 
         [0030]    In accordance with another example embodiment of the present invention, a control method of a fusing system which comprises a fusing unit which comprises a fusing belt which rotates around outer surfaces of at least two rollers which are distanced from each other, and a pressing roller which presses a printing medium together with the fusing belts and fuses an image which is transferred to the printing medium, the control method of the fusing system comprising: preheating the fusing unit so that the temperature of the fusing unit can maintain a printing standby temperature, and standing by for printing until a printing order is applied; controlling a heat source and a driving source so that the fusing belt can be driven when the temperature of the fusing unit increases if the printing order is applied; and controlling the heat source so that the temperature of the fusing unit can maintain a fusing temperature after a printing operation is started. 
         [0031]    According to an aspect of the present invention, the controlling the heat source and the driving source may comprise controlling the heat source so that the temperature of the fusing unit can maintain a preliminary fusing temperature T 2  which is higher than a printing standby temperature T 1 , and lower than a fusing temperature T 3  during an image data processing time before the printing operation is started after the printing order is applied. 
         [0032]    According to another aspect of the present invention, the controlling the heat source and the driving source may comprise respectively turning ON/OFF the heat source and the driving source so that the heat source and the driving source can be driven by a predetermined time unit during the image data processing time. 
         [0033]    In accordance with yet another example embodiment of the present invention, a control method of a fusing system comprises: preheating a fusing unit which fuses an image which is transferred to a printing medium so that the temperature of the fusing unit can maintain a printing standby temperature T 1 , and standing by for printing until a printing order is applied; controlling a heat source which supplies heat to the fusing unit so that the temperature of the fusing unit can maintain a preliminary fusing temperature T 2  which is higher than the printing standby temperature T 1 , and lower than a fusing temperature T 3  during an image data processing time before a printing operation is started after the printing order is applied; and controlling the heat source so that the temperature of the fusing unit can maintain a fusing temperature T 3  after the printing operation is started. 
         [0034]    According to an aspect of the present invention, the controlling the heat source during the image data processing time may comprise turning ON/OFF the heat source so that the heat source can be driven by a predetermined time unit. 
         [0035]    According to an aspect of the present invention, the control method of the fusing system may further comprise controlling a driving source which drives the fusing unit so that the fusing unit can be driven during the image data processing time. 
         [0036]    In addition to the example embodiments and aspects as described above, further aspects and embodiments will be apparent by reference to the drawings and by study of the following descriptions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    A better understanding of the present invention will become apparent from the following detailed description of example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and that the invention is not limited thereto. The spirit and scope of the present invention are limited only by the terms of the appended claims. The following represents brief descriptions of the drawings, wherein: 
           [0038]      FIG. 1  is a schematic view illustrating a fusing system of a typical image forming apparatus; 
           [0039]      FIG. 2  is a flowchart illustrating a temperature control method of the fusing system shown in  FIG. 1 ; 
           [0040]      FIG. 3  is a block diagram illustrating an image forming system employing a fusing system according to an example embodiment of the present invention; 
           [0041]      FIG. 4  is a schematic view illustrating an image forming apparatus in  FIG. 3 ; 
           [0042]      FIG. 5  is a perspective view illustrating a main portion of a fusing system according to a example embodiment of the present invention; 
           [0043]      FIG. 6  is a schematic view illustrating the fusing system according to an example embodiment of the present invention; 
           [0044]      FIG. 7  is a graph illustrating an example of a turning on and off control for a heat source and a driving source depending on a printing process; 
           [0045]      FIG. 8  is a schematic view illustrating a fusing system according to another example embodiment of the present invention; 
           [0046]      FIG. 9  is a flowchart illustrating a control method of a fusing system according to an example embodiment of the present invention; and 
           [0047]      FIG. 10  is a graph illustrating temperature variations of fusing systems according to a comparative example and an example embodiment of the present invention depending on a printing page number variation of the fusing systems. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0048]    Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0049]      FIG. 3  is a block diagram of an image forming system employing a fusing system according to an example embodiment of the present invention, and  FIG. 4  is a schematic view of an image forming apparatus shown in  FIG. 3 . 
         [0050]    As shown in  FIG. 3  and  FIG. 4 , the image forming system includes a host  40 , and an image forming apparatus  100  connected to the host  40 . The host  40  and the image forming apparatus  100  are connected through a bus  50 , such as a serial bus, a parallel bus, or the like. The host  40  sends a printing order to the image forming apparatus  100 , and processes image data for an image forming operation. For this, the host  40  includes an image data processing unit  41  to convert a printing target file into image data which is capable of being printed on a printable medium. Here, for an available emulation, there are a graphic device interface (GDI), a printer control language (PCL) and a post script (PS). When the printing order is applied, time for processing the image data is influenced by the amount of data and the type of the emulation. 
         [0051]    The image forming apparatus  100  includes a control unit  110  for receiving the printing order and the image data from the host  40  and for controlling following elements, a printable medium supplying unit  120 , a developing unit  130  developing a toner image, a transferring unit  140  transferring the toner image formed by the developing unit  130  to a printable medium, a fusing unit  150  fusing the transferred toner image, and a printable medium discharging unit  160 . 
         [0052]    The developing unit  130  includes at least one photosensitive medium  131 , a light scanning unit  133  for scanning a light beam to the photosensitive medium  131  to form an electrostatic latent image, and a development unit  135  for developing the toner image from the electrostatic latent image formed on the photosensitive medium  131 . Here, the photosensitive medium  131 , the light scanning unit  133  and the development unit  135  are provided by each color along a transporting path of the printable medium, and are configured as a tandem type. 
         [0053]    The transferring unit  140  is disposed to face a plurality of photosensitive media  131  to interpose the printable medium M transported through the transporting path therebetween, and transfers the toner image formed on the photosensitive medium  131  to the supplied printable medium M. For this, the transferring unit  140  includes a transferring belt  141  disposed to face the plurality of photosensitive media  131 . 
         [0054]    The fusing unit  150  configures the fusing system according to an example embodiment of the present invention, forms a fusing nip by means of a pressing force, and heats and presses the printable medium passing through the fusing nip to fuse (fix) an image transferred to the printable medium. 
         [0055]    Hereinafter, “printing operation” means a total process forming a visible image to a printable medium based on processed image data, that is, supplying of the printable medium, developing, transferring, fusing and discharging processes. Also, “starting of the printable medium operation” means a point of time in which the printable medium M loaded in a cassette  121  provided to the printable medium supplying unit  120  is picked up by a picking up roller  123 . 
         [0056]      FIG. 5  is a perspective view illustrating a main portion of a fusing system according to an example embodiment of the present invention, and  FIG. 6  is a schematic view illustrating the fusing system according to the example embodiment of the present invention. 
         [0057]    As shown in  FIG. 5  and  FIG. 6 , the fusing system includes a fusing unit  210 , a heat source  221  for supplying heat to the fusing unit  210 , a driving source  225  for driving the fusing unit  210 , a sensing unit  230 , a control unit  110 , and a power source  245 . Here, the control unit  110 , as shown in  FIG. 6 , controls all the components of the image forming apparatus, and is provided as one element of the fusing system according to the present exemplary embodiment of the present invention. 
         [0058]    The fusing unit  210  includes at least one pair of rollers, a fusing belt  215  rotating against an outer surface of the rollers, and a pressing roller  219 . In the example embodiment of the present invention, the pair of rollers includes a fusing roller  211 , and a heating roller  213  distanced from the fusing roller  211  and containing the heat source  221  therein. 
         [0059]    The fusing roller  211  is driven by the driving source  225  to rotate. Here, the fusing belt  215  is driven by means of tension and friction against the fusing roller  211 . Also, the pressing roller  219  is elastically biased toward the fusing roller  211  by means of an elastic member  217  to press the printable medium M together with the fusing roller  211  and the fusing belt  215 . 
         [0060]    Accordingly, a fusing nip N 2  is formed between the fusing roller  211  and the pressing roller  219 , and the fusing belt  215  is rotated within the fusing nip N 2  by means of a friction force and a pressing force. Here, as shown in  FIG. 6 , the pressing roller  219  is driven by means of the friction force against the fusing belt  215 . In the example embodiment of the present invention, the fusing roller  211  is driven by means of the driving source  225 . Alternatively, the heating roller  213  may be driven by means of the driving source  225 . 
         [0061]    The heat source  221  is provided as a halogen lamp, etc. and emits the heat by means of a voltage applied from the power source  245 . A surface of the heating roller  213  is heated by radiation and convection of the heat emitted from the heat source  221 . 
         [0062]    In the example embodiment of the present invention, the heat source  221  is mounted inside the heating roller  213 . Alternatively, the heat source  221  may be mounted inside the fusing roller  211 . 
         [0063]    Here, a portion of the fusing belt  215  contacting to the heating roller  213  is partially heated. Also, in fusing, the heated portion is expanded to the total surface of the fusing belt  215  by means of rotation of the fusing belt  215  so that a fusing temperature can be maintained at a fusing position. 
         [0064]    The sensing unit  230  senses the temperature of the fusing unit  210 , and includes a thermistor  231 , a thermostat  235  and a power switching unit  237 . 
         [0065]    In the example embodiment shown in  FIG. 5  and  FIG. 6 , the thermistor  231  senses a surface temperature of the fusing belt  215  at an area of the fusing belt  215 , and transmits the sensed result to the control unit  110 . The thermistor  231  may include a first thermistor  231   a  positioned to a central portion in a widthwise direction of the fusing belt  215 , and a second thermistor  231   b  positioned to an edge portion thereof. Accordingly, a temperature variation of the central portion and edge portion of the fusing belt  215  can be sensed. 
         [0066]    If the surface temperature of the fusing belt  215  exceeds a predetermined critical temperature, the thermostat  235  blocks the power source  245  applied to the heat source  221  to prevent a fire due to an abnormal control. Also, the power switching unit  237  turns ON/OFF for supplying of the power source  245  to the heat source  221  depending on a control signal from the control unit  110 . 
         [0067]    If the printing order is applied, the control unit  110  controls the heat source  221  and the driving source  225  so that the fusing belt  215  can be driven when the temperature of the fusing unit  210  increases. For this, the control unit  110  compares the temperature sensed by the thermistor  231  with a predetermined critical temperature to control a power supply to the heat source  221  through the power switching unit  237 , and controls the driving source  225  based on a printing proceeding state. Accordingly, the surface temperature of the fusing belt  215  can maintain a printing standby temperature T 1 , a preliminary fusing temperature T 2  or a fusing temperature T 3  depending on a predetermined condition. 
         [0068]    More specifically, the control unit  110  controls the heat source  221  so that the temperature of the fusing unit  210  can maintain the preliminary fusing temperature T 2  which is higher than the printing standby temperature T 1 , and lower than the fusing temperature T 3  during an image data processing time until the printing operation is started after the printing order is received from the host  40  shown in  FIG. 3 . Here, the printing standby temperature T 1  is the temperature of the fusing unit  210  by means of preheating in a printing standby state; and the fusing temperature T 3  is the temperature of the fusing unit  210  during the printing operation. For this, the control unit  110  controls the heat source  221  to drive during the image data processing time. 
         [0069]      FIG. 7  is a graph illustrating an example of a turning ON/OFF control for the heat source and the driving source depending on a printing operation. As shown in  FIG. 7 , section  0 ˜t 1  refers to a state in which the power is not applied to the image forming apparatus; section t 1 ˜t 2  refers to a printing standby state; section t 2 ˜t 3  refers to an image data processing state which is before performing the printing operation but after receiving the printing order; and section after t 4  refers to a fusing state. 
         [0070]    At first, in the printing standby state which is before performing the printing order, the fusing unit  210  is not driven (the driving source  225  is turned OFF), and the heat source  221  is controlled to turn ON/OFF so that the fusing unit  210  can maintain the printing standby temperature T 1 . 
         [0071]    Then, in the section t 2 ˜t 3 , the control unit  110  turns ON/OFF the heat source  221  by a predetermined time unit so that the surface temperature of the fusing belt  215  heated by the heat source  221  can maintain the preliminary fusing temperature T 1 . Here, the preliminary fusing temperature T 2  means value having a predetermined range. The control unit  110  applies the power to the heat source  221  if the surface temperature of the fusing belt  215  sensed by the thermistor  231  deviates from a lower limit value of the preliminary fusing temperature T 2 , and blocks the power applied to the heat source  221  if the surface temperature of the fusing belt  215  deviates from an upper limit value of the preliminary fusing temperature T 2 . Accordingly, although the image data processing time varies due to difference of the type of the emulator and the amount of printing data, the preliminary fusing temperature T 2  having a predetermined range can be maintained. 
         [0072]    Also, the control unit  110  turns ON/OFF the driving source  225  so that the driving source  225  can be driven during the image data processing time. Here, as shown in  FIG. 7 , the turning ON/OFF control of the driving source  225  may be delayed by a predetermined time with respect to a turning ON/OFF control period of the heat source  221 . This is for considering time which is needed to heat the surface of the fusing belt  215  by means of the heat source  221 , and to drive the fusing belt  215  after the surface of the fusing belt  215  is heated to a certain degree. Also, it is unnecessary to synchronize the turning ON/OFF control of the driving source  225  with the turning ON/OFF control of the heat source  221 . The turning ON/OFF control of the driving source  225  may be independently controlled. 
         [0073]    Accordingly, in maintaining the preliminary fusing temperature T 2 , the fusing belt  215  can be prevented from being partially heated, and the total area of the fusing belt  215  can have uniform temperature distribution. Accordingly, if a first part of the fusing belt  215  is preheated to maintain the printing standby temperature T 1 , a second part of the fusing belt  215  stopping for a long time without contacting with the heating roller  213 , especially, a part thereof positioned to the fusing nip N 2  can be supplied with the heat so that the total area of the fusing belt  215  can maintain the preliminary fusing temperature T 2 . 
         [0074]    Finally, if the printing operation is started, the heat source  221  and the driving source  225  are controlled to turn ON/OFF so that the surface temperature of the fusing belt  215  can the fusing temperature T 3 . As shown in  FIG. 7 , the heat source  221  and the driving source  225  continuously maintain the turned ON state in the fusing process. Alternatively, the heat source  221  and the driving source  225  may be turned ON/OFF by a predetermined time unit. 
         [0075]    The fusing system as described above can reduce an temperature increasing time from the preliminary fusing temperature to the fusing temperature if the printing operation is started, and increase the fusing temperature in printing a first page for the printable medium, thereby avoiding an inferior fusing process. 
         [0076]      FIG. 8  is a schematic view illustrating a fusing system according to another example embodiment of the present invention. As shown in  FIG. 8 , the fusing system includes a fusing unit  310 , a heat source  321  for supplying heat to the fusing unit  310 , a driving source  325  for driving the fusing unit  310 , a sensing unit  330 , a control unit  110 , and a power source  345 . Here, the control unit  110  controls all the components of the image forming apparatus, and is provided as one element of the fusing system according to the example embodiment of the present invention. 
         [0077]    The fusing unit  310  includes a fusing roller  311  containing the heat source  221  therein, and a pressing roller  315  elastically biased toward the fusing roller  311 . 
         [0078]    The fusing roller  311  is driven by the driving source  325  to rotate. Also, the pressing roller  315  is elastically biased toward the fusing roller  311  by means of an elastic member  317  to press a printable medium M together with the fusing roller  311 . 
         [0079]    Accordingly, a fusing nip N 3  is formed between the fusing roller  311  and the pressing roller  315 , and as shown in  FIG. 8 , the pressing roller  315  is driven by means of a friction force applied against the fusing roller  311 . 
         [0080]    The sensing unit  330  senses the temperature of the fusing unit  310 , and includes a thermistor  331 , a thermostat  335  and a power switching unit  337 . Here, the sensing unit  330  may have the same configuration as the sensing unit  230  according to an example embodiment of the present invention, shown in  FIG. 6 . 
         [0081]    The control unit  110  compares the temperature sensed by the thermistor  331  with a predetermined critical temperature to control a power supplying to the heat source  321  through the power switching unit  337 , and controls the driving source  325  based on a printing proceeding state. Accordingly, a surface temperature of the fusing roller  311  can maintain a printing standby temperature T 1 , a preliminary fusing temperature T 2  or a fusing temperature T 3  depending on a predetermined condition. Here, the configuration for controlling the surface temperature of the fusing roller  311  to be T 1 , T 2  and T 3 , and driving the fusing unit  310  may be the same as the temperature control and driving control configurations of the fusing unit  210 , shown in  FIG. 6 . 
         [0082]    The fusing systems according to both example embodiments of the present invention as described in connection to  FIG. 6  and  FIG. 8 , can heat the total fusing unit to have the preliminary fusing temperature which is higher than the printing standby temperature and lower than the fusing temperature before performing the printing operation to reduce the temperature increasing time from the preliminary fusing temperature to the fusing temperature if the printing operation is started. In addition, the fusing systems according to both example embodiments of the present invention can increase the fusing temperature in printing a first page for the printable medium, thereby avoiding an inferior fusing process. 
         [0083]      FIG. 9  is a flowchart illustrating a control method of a fusing system according to an example embodiment of the present invention. 
         [0084]    As shown in  FIG. 6  and  FIG. 9 , the control method of the fusing system according to an example embodiment of the present invention includes applying power to an image forming apparatus at block S 10 , standing by for printing at operation S 20 , controlling a fusing unit  210  during an image data processing time before starting a printing operation after applying a printing order at operation S 40 , and controlling the fusing unit  210  to maintain a fusing temperature after starting the printing operation. 
         [0085]    If a power is applied to an image forming apparatus  100  shown in  FIG. 4  at block S 10 , the fusing unit  210  is preheated for reducing a temperature increasing time up to a fusing temperature for printing, and a printing standby state is maintained at operation S 20 . That is, in the present operation, a surface temperature of a fusing belt  215  is sensed by means of a thermistor  231 , and a power is applied to a heat source  221  so that the fusing unit  210  can be preheated to maintain a printing standby temperature Ti at block S 21 . Then, the printing standby state is maintained until the printing order is received from a host  40  at block S 23 . 
         [0086]    Then, whether the printing order is received from the host  40  or not is determined at block S 30  before a preliminary fusing operation or a fusing operation is performed if the printing order is received at operation S 40 . 
         [0087]    The preliminary fusing operation is performed during a time before starting the printing operation after receiving the printing order, that is, during processing the printing data, and the fusing operation is performed after starting the printing operation. For this, the preliminary fusing operation includes determining whether the printing data processing is completed or not after the printing order at block S 41 . 
         [0088]    The preliminary fusing operation controls the heat source  221  and a driving source  225  so that the fusing belt  215  can be driven when the temperature of the fusing unit  210  increases if the printing order is applied. The preliminary fusing operation includes an operation of preheating the fusing unit  210  to maintain the preliminary fusing temperature T 2  at block S 43 , and an operation of preliminarily driving the fusing unit  210  at block S 45 . 
         [0089]    At block S 41 , the fusing unit  210  is supplied with heat so that the fusing unit  210  can maintain the preliminary fusing temperature T 2  which is higher than the printing standby temperature T 1 , and lower than the fusing temperature T 3 . Here, in maintaining the preliminary fusing temperature T 2  at block S 43 , the heat source  221  may be controlled to turn ON/OFF to be driven by a predetermined time unit. 
         [0090]    In the preliminary driving operation of the fusing unit  210  at block S 45 , the driving source  225  is controlled to drive the fusing unit  210  during the image data processing time. Accordingly, in maintaining the preliminary fusing temperature T 2 , the fusing belt  215  can be prevented from being partially heated, and the total area of the fusing belt  215  can have uniform temperature distribution. 
         [0091]    The preliminary driving operation of the fusing unit  210  at block S 45  may be the essentially same as the above described by referring to  FIG. 7 . 
         [0092]    The fusing operation includes an operation of controlling the heat source  221  so that temperature of the fusing unit  210  can maintain the fusing temperature T 3  at block S 51 . Accordingly, the fusing unit  210  is heated by means of the heat emitted from the heat source  221 . Then, a printable medium M is supplied from a printable medium supplying unit  120 , and a toner image transferred to the printable medium M through developing and transferring processes is pressed and heated to perform fusing at block S 53 . 
         [0093]    Hereinafter, a temperature variation of fusing systems according to a comparative example and the example embodiment of the present invention depending on a printing page number variation will be described as follows. 
         [0094]    As shown in  FIG. 10 , the comparative example, which is represented as the solid circles, is a graph illustrating a temperature variation in case of a temperature increase from the printing standby temperature T 1  to the fusing temperature T 3  without preliminary heating and driving. The example embodiment of the present invention, which is represented as the solid triangles, includes the configuration of the fusing system, shown in  FIG. 6 , and is a graph illustrating a temperature variation in the case that the fusing unit  210  is preheated for 30 seconds in a preliminary fusing operation, and then, the temperature increases up to the fusing temperature T 3  after delaying for 15 seconds. The preheating for 30 seconds applies heat of 175° C. to the fusing belt  215  while driving the fusing belt  215  through the driving source  225 . 
         [0095]    As shown in  FIG. 10 , related to the fusing temperature during printing a first page of the printable medium, the fusing temperature according to the example embodiment of the present invention is approximately 152° C., and is higher by approximately 9° C. than the fusing temperature according to the comparative example which is approximately 143° C. Also, the exemplary embodiment totally has a higher temperature distribution in a continuous printing. Accordingly, since the temperature can be maintained to be higher than the printing standby temperature, the temperature can stably vary when increasing up to the fusing temperature. 
         [0096]    As described above, the present invention provides a fusing system and a control method thereof preliminarily driving a fusing unit during an image data processing time before a printing operation is started after a printing order so that the fusing unit can maintain a preliminary fusing temperature which is higher than a printing standby temperature. Accordingly, a temperature increasing time up to a fusing temperature can be reduced in performing the printing operation which has continuous processes of supplying a printable medium, developing, transferring and fusing, thereby reducing time for a first page printing. Also, the fusing temperature in starting printing can be increased, thereby avoiding an inferior fusing process when printing a first page of a printable medium. 
         [0097]    While there have been illustrated and described what are considered to be example embodiments of the present invention, it will be understood by those skilled in the art and as technology develops that various changes and modifications, may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. Many modifications, permutations, additions and sub-combinations may be made to adapt the teachings of the present invention to a particular situation without departing from the scope thereof. Accordingly, it is intended, therefore, that the present invention not be limited to the various example embodiments disclosed, but that the present invention includes all embodiments falling within the scope of the appended claims.