Patent Publication Number: US-6907204-B2

Title: Method of controlling power of a fixing device of electro-photographic image forming apparatus in print standby mode

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2002-35414, filed Jun. 24, 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 method of controlling the power of a fixing device of an electro-photographic image forming apparatus, and more particularly, to a method of controlling the power of a fixing device employing a heat pipe in a print standby mode, by which instantaneous heating and low power consumption are possible. 
   2. Description of the Related Art 
   Electro-photographic image forming apparatuses include a fixing device to fix a toner image on a sheet by temporarily fusing toner image powder on the sheet on which the toner image has been transferred. The fixing device includes a fusing roller to fix the toner on the sheet and a pressure roller to press the sheet against the fusing roller. 
     FIG. 1  is a schematic longitudinal cross-section of a conventional fusing roller in which a halogen lamp serves as a heat source.  FIG. 2  is a schematic latitudinal cross-section of a fixing device adopting the fusing roller of FIG.  1 . 
   Referring to  FIG. 1 , a fusing roller  10  includes a cylindrical roller  11  and a halogen lamp  12  installed at the center of the inside of the cylindrical roller  11 . A coated layer  11   a  (for example, coated with TEFLON) is formed on the circumference of the cylindrical roller  11 . The halogen lamp  12  generates heat within the cylindrical roller  11 , and accordingly the cylindrical roller  11  is heated by radiant heat from the halogen lamp  12 . 
   Referring to  FIG. 2 , a pressure roller  13  is located beneath the fusing roller  10  while having a sheet  14  between the pressure roller  13  and the fusing roller  10 . The pressure roller  13  is elastically supported by a spring  13   a  and presses the sheet  14  between the fusing roller  10  and the pressure roller  13  against the fusing roller  10  with a predetermined pressure. Toner image powder  14   a  formed on the sheet  14  is fixed on the sheet  14  by the predetermined pressure and heat while passing between the fusing roller  10  and the pressure roller  13 . 
   At one side of the fusing roller  10  are installed a thermistor  15  to measure a surface temperature of the fusing roller  10 , and a thermostat  16  to block power supplied to the halogen lamp  12  if the surface temperature of the fusing roller  10  exceeds a predetermined temperature. The thermistor  15  measures the surface temperature of the fusing roller  10  and transmits an electrical signal of the measured surface temperature to a controller (not shown) of a printer (not shown). The controller controls the amount of power supplied to the halogen lamp  12  depending on the measured surface temperature in order to maintain the surface temperature of the fusing roller  10  within a predetermined temperature range. If the temperature of the fusing roller  10  exceeds a temperature limit due to malfunctions of the thermistor  15  and the controller, the thermostat  16  blocks power flowing to the halogen lamp  12  by opening a contact (not shown). 
   The fusing roller  10  employing the halogen lamp  12  as a heat source consumes a great amount of power and has a low temperature increase rate. In particular, when the power of an image forming apparatus is turned on, a significantly long warm up is needed. 
     FIG. 3  is a graph showing a temperature profile with respect to a timing of alternating current (AC) power supplied to the halogen lamp  12  of the conventional fusing roller  10 . Referring to  FIG. 3 , t 1  denotes a time to operate an image forming apparatus, and t 2  denotes a time when the temperature of the fusing roller  10  of the image forming apparatus reaches a target fusing temperature (185° C.). The interval between t 1  and t 2  denotes the warm-up period of the fusing roller  10 . During the interval between t 1  and t 2 , an AC voltage is continuously supplied to the halogen lamp  12 , a temperature increase rate of the fusing roller  10  is 4-5° C./sec, and the warm-up period is about 35-40 seconds. 
   The interval between t 2  and t 3  denotes a print mode interval, and t 3  denotes a time when the image forming apparatus enters into a print standby mode. During the interval between t 2  and t 3 , the supply of power (i.e., the turning on and off of power) to the halogen lamp  12  is controlled in order to maintain the temperature of the fusing roller  10  at a predetermined temperature. For ease of illustration, frequent AC power on-off control is indicated by AC power ‘on’ in FIG.  3 . 
   At t 3 , power is not supplied to the halogen lamp  12 , and thus the temperature of the fusing roller  10  decreases. Given that the temperature rising rate of the conventional fusing roller  10  is 4-5° C./sec, and the time to change from the print standby mode to the print mode is less than 10 seconds, the temperature of the fusing roller  10  must be maintained at about 140° C. Hence, if the temperature of the fusing roller  10  is cooled from 185° C. to about 140° C., power is supplied to the halogen lamp  12 , at t 4 . The supply of power (i.e., whether to supply power or not) to the halogen lamp  12  is controlled to maintain the temperature of the fusing roller  10  at the predetermined temperature. For ease of illustration, frequent AC power on-off control is indicated by AC power ‘on’ in FIG.  3 . 
   In the case when the halogen lamp  12  is used as the heat source of the fusing roller  10 , since a temperature of the fusing roller  10  rises at 4-5° C./sec, the surface temperature of the fusing roller  10  must be maintained at a relatively high temperature, about 140° C., in order to adjust a first print out time (FPOT) during a change from the print standby mode to the print mode in 10 seconds. Thus, a great amount of power is consumed in the print standby mode. Generally, in the case of a halogen lamp of 400 to 500 Watt/hour, power of about 250 Watt/hour is consumed in the print mode, and power of about 70 Watt/hour is consumed in the print standby mode. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide a method of controlling power supplied to a fixing device in a print standby mode to obtain a short FPOT upon a change from the print standby mode to a print mode and reduce the amount of power consumed in the print standby mode. 
   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 foregoing and/or other aspects are achieved by providing a method of controlling power of a fixing device of an electro-photographic image forming apparatus in a print standby mode. The electro-photographic image forming apparatus includes the fixing device having a heat pipe which contains a working fluid, to fix toner onto a sheet; a power supply to supply power to a heater installed in the fixing device; a fusing temperature measurer to measure the temperature of the fixing device; and a controller to compare the temperature measured by the fusing temperature measurer with a predetermined temperature and to control power from the power supply to the heater. In the method, it is determined whether the electro-photographic image forming apparatus is in a print standby mode. If it is determined that the electro-photographic image forming apparatus is in the print standby mode, the temperature of the fixing device is adjusted within the range from a first predetermined temperature, which is a high temperature, to a second predetermined temperature, which is a low temperature. The temperature of the fixing device increases from the second predetermined temperature to an operation temperature within 10 seconds, and the second predetermined temperature is 100° C. or less. 
   The second predetermined temperature may be 85° C. or less, and the amount of power consumed by the fusing roller during the standby mode may be 20 Watt/hour or less. 
   In the print standby mode determination operation, if a first predetermined period of time lapses after a print operation in a print mode, or if the print standby mode is within a second predetermined period of time, it is determined that the electro-photographic image forming apparatus is in the print standby mode. 
   Alternatively, if a predetermined signal is received from an external input unit, it is determined that the electro-photographic image forming apparatus is in the print standby mode. 
   The temperature of the fixing device may be adjusted by measuring the temperature of the fixing device, comparing the measured temperature with the second predetermined temperature, blocking power from going to the heater if the measured temperature is greater than the second predetermined temperature, and supplying power to the heater if the measured temperature is smaller than the second predetermined temperature. 
   In the power supplying operation, power is supplied to the heater until the measured temperature of the fixing device increases to the first predetermined temperature. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or 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 schematic longitudinal cross-section of a conventional fusing roller in which a halogen lamp serves as a heat source; 
       FIG. 2  is a schematic latitudinal cross-section of a fixing device adopting the fusing roller of  FIG. 1 ; 
       FIG. 3  is a graph showing a temperature profile of the conventional fusing roller of  FIG. 1 and a  timing of AC power supplied to the halogen lamp; 
       FIG. 4  is a schematic longitudinal cross-section of a fixing device of an electro-photographic image forming apparatus to which a power controlling method according to an embodiment of the present invention is applied; 
       FIG. 5  is a block diagram of a power controlling apparatus for performing a power controlling method for a fixing device according to an embodiment of the present invention; 
       FIG. 6  is a graph showing a temperature profile of the fusing roller of  FIG. 4 and a  timing of AC power supplied to the heater of  FIG. 5 ; and 
       FIG. 7  is a flowchart illustrating a power controlling method for the fixing device of  FIG. 4 , according to the embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the present preferred embodiment of the present invention, an example of which is illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
   Referring to  FIG. 4 , a fixing device  100  includes a fusing roller  110  and a pressure roller  130 . The fusing roller  110  rotates in a direction ‘A’ to discharge a sheet  150  having a toner image  151  thereon. The pressure roller  130  is installed on the bottom surface of the sheet  150  whose upper surface contacts the fusing roller  110 , and rotates in direction ‘B’ while pressing the sheet  150  against the fusing roller  110 . 
   To be more specific, the fusing roller  110  includes a cylindrical roller  112 , a heater  113 , and a heat pipe  114 . A toner protective layer  111  coated with TEFLON is formed on the cylindrical roller  112 . The heater  113  is spirally installed on an inner surface of the cylindrical roller  112  to receive electricity from an external power source and generate heat. The heat pipe  114  is installed on an inner surface of the heater  113  and has both ends sealed. The heat pipe  114  contains a working fluid  115  with a predetermined volume. 
   A thermistor  118  is installed above the toner protective layer  111  and measures the surface temperature of the fusing roller  110 . A thermostat  119  is installed over the fusing roller  110  and blocks power from going to the heater  113  to prevent overheating if the surface temperature of the fusing roller  110  sharply increases. The heater  113  may be a resistive heating coil which spirally wraps around the heat pipe  114 . 
   The heat pipe  114  is made airtight by closing both ends, and contains a predetermined amount of the working fluid  115 . The working fluid  115  is vaporized by heat received from the heater  113  and transmits the heat of vaporization to the cylindrical roller  112  so that the entire cylindrical roller  112  is evenly heated within a short period of time without a temperature deviation of the surface of the cylindrical roller  112 . The working fluid  115  occupies 5-50%, i.e., 5-15%, of the volume of the heat pipe  114 . A volume percentage of the working fluid  115  that is less than 5% may result in dry out. 
   The material of the working fluid  115  can be selectively used depending on the material of the heat pipe  114 . In other words, if the heat pipe  114  is made of stainless steel, the working fluid  115  can be any one of well-known working fluids except for water, for example, FC-40(3M). 
   If the heat pipe  114  is made of copper (Cu), the working fluid  115  can be any one of well-known working fluids including water, i.e., distilled water. The use of water lowers manufacturing costs and does not cause environmental pollution. 
   The cylindrical roller  112  is heated by heat received from the heater  113  or by the heat of vaporization from the working fluid  115  contained in the heat pipe  114  in order to fuse the toner image  151  formed on the sheet  150  and fix the same onto the sheet  150 . The cylindrical roller  112  is made of stainless steel, aluminium (Al), or copper (Cu). 
     FIG. 5  is a block diagram of a power controlling apparatus to perform a power controlling method for a fixing device according to the embodiment of the present invention. Referring to  FIG. 5 , a fusing temperature measurer  162  measures the surface temperature of the fusing roller  110  at intervals of a predetermined period, e.g., 100 ms. 
   An analog value corresponding to a temperature measured by the fusing temperature measurer  162  is converted into a digital value by an analog-to-digital converter (ADC)  164 , and the digital value is transmitted to a controller  166 . 
   The controller  166  performs calculations necessary to control the electro-photographic forming apparatus. That is, the controller  166  compares the measured temperature with a predetermined temperature and outputs a signal to control a heater  170  to an AC power supply  168 . The AC power supply  168  supplies or blocks AC power to the heater  170  based on the control signal of the controller  166 , that is, an on-off signal. 
   The fusing temperature measurer  162  and the heater  170  correspond to the thermistor  118  and the heater  113  of  FIG. 4 , respectively, and accordingly, will not be described in greater detail. 
     FIG. 6  is a graph showing a temperature profile of the fusing roller  110  of  FIG. 4 and a  timing of the AC power supplied to the heater  170  of  FIG. 5 , with respect to time. 
   In the graph of  FIG. 6 , t 1  denotes a time to operate the electro-photographic image forming apparatus, and t 2  denotes a time when the temperature of the fusing roller  110  of the electro-photographic image forming apparatus reaches a target fusing temperature, i.e., 185° C. The interval between t 1  and t 2  denotes a warm-up period of the fixing device  100 . During the interval between t 1  and t 2 , an AC voltage is continuously supplied to the heater  170 . A temperature increase rate of the fusing roller  110  is 8-15° C./sec, and the warming-up period is about 10-20 seconds. 
   The interval between t 2  and t 3  denotes a print mode interval, and t 3  denotes a time when the electro-photographic image forming apparatus enters into a print standby mode. During the interval between t 2  and t 3 , the supply of power (i.e., whether to supply power or not) to the heater  170  is controlled in order to maintain the temperature of the fusing roller  110  at a predetermined temperature. For ease of illustration, in  FIG. 6 , frequent AC power on-off control is indicated by AC power ‘on’. 
   At t 3 , power is blocked from going to the heater  170 , and thus the temperature of the fusing roller  110  decreases. Here, the temperature cooling rate of the fusing roller  110  varies from 5 to 10° C./min depending on the type of the working fluid  115 , the usage amount of the working fluid  115 , the material of the heat pipe  114 , or the like. After t 4 , when the temperature of the fusing roller  110  measured by the fusing temperature measurer  162  reaches a certain temperature, e.g., 80° C., the controller  166  increases the temperature of the fusing roller  110  to 140° C. In other words, during the interval between t 4  and t 5 , AC power is supplied to the heater  170 . If the temperature increasing speed of the fusing roller  110  is 10° C./sec, the AC power can be supplied to the heater  170  for about 6 seconds. Thereafter, at t 5 , if a power supply to the heater  170  is cut off, the fusing roller  110  is again cooled. Here, if the cooling rate of the fusing roller  110  is 6° C./min, the cooling time is about 10 minutes. In the print standby mode, cooling and increasing the temperature of the fusing roller  110  are repeated, and the power consumed by the fusing roller  110  is about 17 Watt/hour. 
     FIG. 7  is a flowchart illustrating a method of controlling power supplied to the fixing device  100  in a print standby mode, according to the embodiment of the present invention. Referring to  FIGS. 4 through 7 , in S 10 , the fusing temperature measurer  162  measures the temperature of the fusing roller  110  at intervals of a predetermined period, e.g., 100 ms and transmits an analog signal associated with the measured temperature to the ADC  164 , and the ADC  164  converts the received analog signal into a digital signal and outputs the digital signal to the controller  166 . 
   In S 12 , the controller  166  determines whether the electro-photographic image forming apparatus is in a print standby mode. The controller  166  determines that the electro-photographic image forming apparatus is in the print standby mode if no new print operations exist until a first predetermined period of time lapses after the previous print operation has been completed. Alternatively, a user may input a print standby mode to the controller  166  using an external input unit. If no new print operations exist in the print standby mode within a second predetermined period of time, the print standby mode is changed to an energy saving mode. Accordingly, the supply of power to the heater  170  is blocked until a print operation is commanded. 
   In S 14 , if it is determined in S 12  that the electro-photographic image forming apparatus is in a print standby mode, the controller  166  compares the temperature of the fusing roller  110  with a predetermined temperature, e.g., 80° C. 
   On the other hand, if it is determined in S 12  that the electro-photographic image forming apparatus is not in a print standby mode, the method goes back to S 10 . 
   If it is determined in S 14  that the temperature of the fusing roller  110  is greater than the predetermined temperature, the controller  166  blocks power from going to the heater  170 , in S 20 . 
   On the other hand, if it is determined in S 14  that the temperature of the fusing roller  110  is equal to or less than the predetermined temperature, power is supplied to the heater  170 , in S 16 . 
   In S 18 , it is determined whether the time required to supply power to the heater  170  exceeds a predetermined period of time, e.g., 6 seconds. 
   If it is determined in S 18  that power is supplied during the predetermined period of time, the method goes to S 20 , and accordingly power is blocked from being supplied to the heater  170 . On the other hand, if it is determined in S 18  that the predetermined period of time has not passed, a power supply to the heater  170  is continued. 
   As described above, in a method of controlling power supplied to a fusing roller in a print standby mode, an FPOT upon a change from a print standby mode to a print mode is maintained at about 10 seconds or less, and simultaneously power consumption in the print standby mode is reduced about 75% due to a short period of power provision to the fusing roller and a long cooling period of the fusing roller. 
   Although an embodiment of the present invention has been shown and described, it will be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.