Abstract:
A control method to control a lamp, which is used as a heat generator, including detecting a temperature of lamp, comparing the detected temperature of the lamp with a predetermined reference temperature, turning off a power supply to the lamp when the detected temperature of the lamp exceeds the predetermined reference temperature, and when the lamp stays in a turned-off state for more than a first time amount, supplying a half wavelength pulse to the lamp at intervals according to a second time amount. According to the lamp control method, reducing the inrush of current to the lamp is possible without requiring additional hardware. When applied to electronic apparatuses, the lamp control method reduces maximum value of the inrush of current in the stand-by mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of Korean Patent Application No. 2003-65819, filed on Sep. 23, 2003, 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 a lamp control method, and, in particular to a lamp control method to minimize an inrush of current and a method of controlling an image forming apparatus to reduce an inrush of current by using the lamp control method.  
         [0004]     2. Description of the Related Art  
         [0005]     In general, light emission devices using a resistance of filament, such as incandescent lamps or halogen lamps, are widely used to heat treat or in common illumination, and, as for laser printers, such light emission devices are applied as fixing rollers to fix toner powder onto a paper.  
         [0006]     Incandescent lamps usually take a form of a glass bulb, into which an inert gas such as argon (Ar) or neon (Ne) is introduced and in which a large tungsten filament is provided. Conversely, halogen lamps generally take a form of a glass bulb, into which a halogen gas is introduced so as to obtain a high brightness property. Typically, halogen lamps have a color temperature characteristic that is close to that of sunlight. Within a halogen lamp, a halogen gas may adhere to a tungsten filament to form a halogen compound. However, the halogen compound formed in such a way has a characteristic such that the halogen compound is decomposed when the internal temperature of the halogen lamp is high. Therefore, a black spot phenomenon, which causes a part of a lamp to be blackened, may occur. Nevertheless, most halogen elements that decompose from the halogen compound tend to adhere to the filament so as to lengthen the life of the filament. In addition, the surfaces of halogen lamps are typically capable of being heated to several hundred degrees centigrade depending on manufacturing processes thereof. Therefore, they are largely employed as heating elements. Accordingly, halogen lamps are often applied as fixing rollers to fix toner powder onto a paper, such as in a laser printer. Hereinbelow, the case in which a halogen lamp is applied as a heating element is described.  
         [0007]      FIG. 1  conceptually illustrates a method of controlling a halogen lamp that is incorporated within a conventional fixing roller.  
         [0008]     As shown in the drawing, a conventional halogen lamp  11  is driven by an AC power source  10 . A triac  15  is connected between the AC power source  10  and the halogen lamp  11 . The triac  15  is turned on/off by DC voltage applied from a switching section  13  so as to turn the interconnection between the halogen lamp  11  and the AC power source  10  on/off. A sensor  14  measures the temperature of the halogen lamp  11  and applies the measured temperature to the switching section  13 . The switching section  13  performs on/off control of the triac  15  and is driven by DC current supplied from a rectifier  12 .  
         [0009]     Typically, the switching section  13  controls the triac  15  in such a manner that when a temperature detected by the sensor exceeds a preset temperature the switching section  13  turns off the triac  15  and when the detected temperature is lower than the preset temperature the switching section  13  turns on the triac  15 .  
         [0010]      FIG. 2  is a graph showing a driving characteristic of the halogen lamp  11  shown in  FIG. 1 . The graph shows the driving characteristic in relation to inflowing current (I) versus time (t) axes. As shown in the drawing, the halogen lamp  11  consumes the most current at the time when power is applied to the halogen lamp  11 , i.e., at the time when the halogen lamp  11  is started. Concurrently, after a length of time has passed, a large amount of current is no longer required to drive the halogen lamp  11 . This is due to the fact that when the filament (not shown) included within the halogen lamp has a lower temperature, e.g., when no power is applied, the filament (not shown) has a lower resistance value. Here, a large amount of electric current will pass through the filament. Conversely, when power is applied to the filament to preheat the filament, the filament has a higher resistance value. Here, a small amount of electric current will pass through the filament. The point “A” in the drawing indicates a peak electric value passing through the halogen lamp  11  as the AC power source  10  is inputted, when the halogen lamp  10  has a lower temperature. Such electric current is defined as “inrush current,” wherein if a halogen lamp consumes a larger amount of electric power, the inrush current will be increased. In this regard, a problem arises in that as a halogen lamp, which consumes a large amount of electric power consumption, is driven, electric power supplied to an electronic appliance (not shown) located around the halogen lamp is reduced due to the large amount of inrush of current provided to the halogen lamp. As a result, the electronic appliance may malfunction.  
         [0011]      FIG. 3  shows an example of control pulses applied to the triac  15  from the switching section  13 . When the twenty cycles constitute one period, the shown pulses indicate that only a quarter of applied AC power source  10  is applied to the halogen lamp  11 . As a result, the temperature of the halogen lamp  11  is controlled by the AC power source  10 . The AC power source  10 , in this case may be limited to a quarter of the total AC power that is applied to the halogen lamp  11 . The points at which an AC cycle is turned either from positive (+) to negative (−) or from negative (−) to positive (+) during AC cycles by the AC power source  10  are defined as zero-crossing. However, when the halogen lamp  10  is restarted in the state in which a temperature thereof has been lowered, there is a problem in that a large amount of inrush current flows in the halogen lamp  11 .  
         [0012]      FIG. 4  illustrates another example of control pulses applied to the triac  15  from the switching section  13  shown in  FIG. 1 . The illustrated pulses are those taken by slicing the pulses of the AC power source  11  according to the temperature of the halogen lamp  11 . Among the illustrated pulses, the black areas C comprise a waveform of the AC power source passing through the triac  15  under the control of the switching section  13 . The electric power applied to the halogen lamp  11  increases or decreases through a control such that, as the temperature increases the size of black areas C decreases while the size of white areas B increases. Such a control method is defined as a phase control method. Here, controlling the temperature of the halogen lamp by controlling the electric power practically applied to the halogen lamp  11  is possible. In a phase control method, if the temperature of the halogen lamp  11  is very high, the width of areas C will be reduced. As the width of areas C is reduced, the waveform of electric current, which passes through the halogen lamp  11  and the triac  15 , approaches an impulse or harmonic. As a result however, a noise may be applied to an electronic appliance (not shown) positioned around the halogen lamp.  
       SUMMARY OF THE INVENTION  
       [0013]     Accordingly, an aspect of the present invention provides a lamp control method to reduce the inrush of current to the lamp, which is used as a heating element, without generating a harmonic, and a method of controlling an image forming apparatus to reduce the inrush of current to the image forming apparatus.  
         [0014]     The above aspect of the present invention may be achieved by providing a lamp control method, comprising detecting a temperature of a lamp, comparing the detected temperature of the lamp with a predetermined reference temperature, turning off a power supply to the lamp when the detected temperature of the lamp exceeds the predetermined reference temperature, and when the lamp stays in turned-off state more than a first time amount, supplying a half wavelength pulse to the lamp at intervals according to a second time amount.  
         [0015]     The power supply may be switched in accordance with one of the methods of zero-crossing control and phase control.  
         [0016]     According to another aspect of the present invention, a lamp control method of an image forming apparatus comprises detecting a temperature of a lamp which heats a fixing roller of the image forming apparatus, turning off a power supply to the lamp when the detected temperature of the lamp exceeds a predetermined reference temperature, and when the lamp stays in turned-off state more than a first time amount, supplying a half wavelength pulse to the lamp at intervals according to a second time amount.  
         [0017]     The predetermined reference temperature may be set with respect to a stand-by mode of the image forming apparatus.  
         [0018]     The predetermined reference temperature may be set with respect to a printing mode of the image forming apparatus.  
         [0019]     The power supply may be switched in accordance with one of the methods of zero-crossing control and phase control.  
         [0020]     The lamp comprises a halogen lamp.  
         [0021]     The supplying the half wavelength pulse to the lamp at intervals according to the second time amount may be performed when the image forming apparatus is in a stand-by mode.  
         [0022]     According to another aspect of the present invention, a lamp control method comprises detecting a temperature of a lamp, based on the detected temperature, supplying a switching-controlled power to the lamp to maintain the lamp at a predetermined temperature, and supplying a half wavelength to the lamp when the lamp stays off for more than a first time amount during the switching of the power supply.  
         [0023]     The power supply may be provided to the lamp in accordance with one of the methods of zero-crossing control and phase control.  
         [0024]     The lamp comprises a halogen lamp.  
         [0025]     The supplying the half wavelength pulse is performed when the temperature of the lamp reaches and maintains the predetermined temperature.  
         [0026]     Additional and/or other 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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0028]      FIG. 1  is a view to conceptually illustrate a method of controlling a halogen lamp incorporated within a conventional fixing roller;  
         [0029]      FIG. 2  is a graph showing a driving characteristic of the halogen lamp shown in  FIG. 1 ;  
         [0030]      FIG. 3  is a view showing an example of pulses applied to a triac from a switching section shown in  FIG. 1 ;  
         [0031]      FIG. 4  is a view of another example of pulses applied to the triac from the switching section shown in  FIG. 1 ;  
         [0032]      FIG. 5  is a view showing an embodiment for a fixing roller of an image forming apparatus and a peripheral circuit to control the fixing roller to execute the inventive lamp control method;  
         [0033]      FIG. 6  is a view showing another form of a pulse applied to the fixing section from a switching section;  
         [0034]      FIG. 7  is a flowchart showing a lamp controlling method to reduce an inrush of current according to an embodiment of the present invention;  
         [0035]      FIG. 8  is a flowchart showing a method to control a standby mode of the fixing section of an image forming apparatus by using a lamp control method to reduce an inrush of current according to an embodiment of the present invention; and  
         [0036]      FIG. 9  is a flowchart showing a lamp controlling method to reduce an inrush of current according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0037]     Reference will now be made in detail to the 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 below to explain the present invention by referring to the figures.  
         [0038]      FIG. 5  shows an embodiment of a fixing roller of an image forming apparatus and a peripheral circuit to control the fixing roller to execute the inventive lamp control method.  
         [0039]     The fixing roller and the peripheral circuit to control the fixing roller comprise a switching mode power supply (SMPS)  110 , a read only memory (ROM)  120 , a control section  130 , a switching section  140 , and a fixing section  150 .  
         [0040]     The SMPS  110  rectifies commercial alternating current (AC) to generate various direct voltages as are required by the image forming apparatus. The ROM  120  stores various control programs to drive the image forming apparatus. A control program stored in the ROM  120  controls the temperature of the fixing section  150 . The control section  130  controls the switching section  140  in accordance with the control program stored in the ROM  120 . When the image forming apparatus operates in a stand-by mode, i.e., in a waiting state, a temperature of the fixing section  150  should be maintained at a predetermined temperature. At this time, if electric power is not supplied to the fixing section  150  over a long time, the temperature of the heating element to heat the fixing section  150  occasionally decreases excessively. If the temperature of the heating element decreases excessively, an inrush of current is generated so as to restart the fixing section  150 . The fixing section  150  comprises two rollers  151 ,  152  to heat and compress toner adhered to a paper P, in which one of the two rollers  151 ,  152  (e.g., the roller  151 ) is provided with a lamp  151   a  that is driven by electric power supplied from the SMPS  110 . According to an embodiment of the invention, the lamp  151  is a halogen lamp that has a long life and generates a high temperature. Even if the roller  151  is maintained at a predetermined temperature, a large amount of electric current is required to heat the filament (not shown) of the lamp  151   a  when the lamp  151   a  is restarted if the lamp  151   a  is cooled. Accordingly, a voltage applied to an electronic appliance located around the image forming apparatus may be reduced as described above with reference to  FIG. 2 . The present invention solves this problem by driving the lamp  150  at predetermined intervals.  
         [0041]      FIG. 5  shows a form of pulses applied to the fixing section  150  from the switching section  140 . The interval “A” indicates a control pulse interval to keep the temperature of the lamp  151   a  constant, and the interval “B” indicates the form of pulses, which are applied to the lamp  151   a  when the fixing rollers  151 ,  152  are heated to a predetermined temperature by the lamp  151   a . In the interval “A,” a series of control pulses maintain the temperature of the fixing section and in the interval “B,” a series of pulses prepare the lamp  151   a  to be restarted in the interval during which the lamp  151   a  is turned off. The time interval T between each pair of pulses may have various values depending on heat generating and heat emitting characteristics of the heating element. Here, control of the temperature of the lamp  151   a  may be performed according to various control methods. After the temperature of the lamp  151   a  reaches a proper value, the filament of the heating element may be maintained at a predetermined temperature by applying a half-wavelength pulse to the lamp  151  at predetermined time intervals depending on the heat generating and heat emitting characteristics of the lamp  151   a.  As a result, if the temperature of the lamp  151   a  is controlled, no harmonic will be generated in the image forming apparatus provided with such a lamp  151   a  and reducing an inrush of current will be possible.  
         [0042]      FIG. 6  shows another form of pulses that are applied to the fixing section  150  from the switching section  140 . As illustrated in the interval “C,” pulses adjust the temperature of the lamp  151   a  to a desired temperature, and as illustrated in the interval “D,” half-wavelength pulses are each applied to the lamp  151   a  at predetermined time intervals when the lamp  151   a  is heated to the desired temperature. In the interval “C”, a series of pulses are applied according to a phase control method. The phase control method is a useful method to reduce an inrush of current. If a series of pulses according to the phase control method are applied to the lamp  151   a,  the pulses shown in the interval “D” may reduce an inrush of current but a harmonic noise that is peculiar to the phase control method may be produced.  
         [0043]      FIG. 7  shows a flowchart of an embodiment of the inventive lamp control method to reduce an inrush of current.  
         [0044]     First, electric power is applied to a lamp  151   a  that is employed as a heating element to heat the lamp, and the temperature of the lamp  151   a  is detected ( 200 ). In an embodiment of the invention, the temperature of the lamp is detected using a temperature sensor such as the sensor  153 , which is attached onto or adjacent to the surface of the lamp  151   a . Next, a reference temperature value is set depending on the use of the lamp  151   a  which is then compared with the detected temperature to confirm whether the detected temperature exceeds the reference temperature value ( 210 ). To this end, the sensor  153  and hardware to switch the power supply to the lamp  151   a  in accordance with temperature detected by the sensor  153  may both be required. The above-mentioned hardware may be hardware that is generally provided in a device to drive the lamp  151   a .  FIG. 5  illustrates one example of the image forming apparatus having the above-mentioned structure, in which the temperature detected by the temperature sensor  153  is compared with the reference temperature value stored in the ROM  120  in the control section  130 , and the control section  130  controls the switching section  140  depending on the comparison result. The switching section  140  turns off the lamp  151   a  when the temperature of the lamp  151   a  exceeds the reference value ( 230 ) and maintains the temperature of the lamp  151   a  by switching the power supply to the lamp  151   a  when the temperature of the lamp  151   a  is in the reference value range ( 220 ). Here, the “reference value” is a value within upper and lower limits. The upper and lower limits are preset depending on the use of the lamp  151   a . Next, if electric current to the lamp  151   a  stays in an off-state for a predetermined time period, the control section  130  applies a half-wavelength pulse to the lamp  151   a  at predetermined time intervals ( 250 ). In various embodiments of the invention, the application of the half-wavelength pulses to the lamp  151   a  by the control section occurs if electric current to the lamp  151   a  stays in the off-state for approximately 300 ms-900 ms. Further, the predetermined time intervals during which the half-wavelength pulses are applied to drive the lamp  151   a  may be approximately 500 ms. In this manner, the filament incorporated within the lamp  151   a  will be maintained at a predetermined temperature and an excessive inrush of current will not be generated when the lamp  151   a  is heated.  
         [0045]      FIG. 8  shows another embodiment according to the inventive method of controlling an image forming apparatus, to which the inventive lamp control method for reducing inrush current is applied.  
         [0046]     First, an image forming apparatus (e.g., printer, facsimile, scanner, copier, etc.) is powered-on ( 310 ) so as to heat a fixing section  150  provided in the image forming apparatus ( 320 ). The fixing section  150  comprises a sensor  153  to detect the temperatures of a pair of rollers  151 ,  152  to compress and thermally transfer toner or ink adhered on a paper P. In addition, a halogen lamp  151   a  is incorporated in the roller  151  to heat the roller  151 . The halogen lamp  151   a  comprises a filament and a glass bulb, in which a halogen gas is introduced. Such a halogen lamp projects light with very high brightness and a surface thereof is heated up to several hundred degrees centigrade. When the halogen lamp  151   a  is heated, the heat of the halogen lamp  151   a  is transferred to the roller  151 . Next, the sensor  153  converts the detected temperature of the roller  151  into a digital signal and applies the digital signal to a control section  130 . The control section  130  compares the temperature detected by the sensor  153  with a temperature previously stored in a ROM  120  ( 330 ). For example, as the proper temperature is typically 80° C. to 140° C. when the image forming apparatus is in the stand-by mode, and typically 170▾ to 200▾ in the printing mode, the control section  130  determines whether the detected temperature is within the range of 80° C. to 140° C. when the image forming apparatus is in the stand-by mode, and whether the detected temperature is within the range of 170° C. to 200° C. when the image forming apparatus is in the printing mode. If the temperature detected by the sensor  153  is determined to be out of the proper temperature range (80° C. to 140° C. in stand-by mode, and 170° C. to 200° C. in printing mode), power supply to the lamp  151   a  is turned off ( 350 ).  
         [0047]     Next, the control section  130  switches the electric current supply to the lamp  151   a , so that the temperature of the roller  151  may be maintained within the proper temperature range, for example, within the range of 170° C. to 200° C. when in printing mode ( 340 ). The electric current supply to the halogen lamp  151   a  may be in pulse form, and the pulse may have an appropriate form according to zero-crossing or phase control. When a predetermined time, 300 ms to 900 ms for instance, elapses after the power-off of the halogen lamp  151   a  ( 360 ), the control section  130  regularly applies a half-wavelength pulse to the lamp  151   a  at predetermined time intervals to maintain the driving of the lamp  151   a  ( 370 ). In this manner, the lamp  151   a  is maintained at a predetermined temperature range, which, in an embodiment of the invention, may be approximately 170° C.˜180° C. in printing mode. As a result, an excessive inrush of current is avoided.  
         [0048]     As is described above, according to the present invention, a reduction of an inrush of current to a lamp employed as a heating element is possible without a need to provide separate hardware.  
         [0049]      FIG. 9  is a flowchart of a lamp control method to reduce an inrush of current according to another embodiment of the present invention.  
         [0050]     First, electric current is applied to the lamp  151   a , which is employed as a heating generator, and the temperature of the heated lamp  151   a  is detected ( 420 ). The temperature may be detected by the temperature sensor such as the sensor  153  which is attached onto or adjacent to the surface of the lamp  151   a . Next, based on the detected temperature, electric current, which is switched by the zero-crossing pulse or phase-control slicing pulse, is supplied to the lamp  151   a  so that the lamp  151   a  may reach a predetermined temperature range ( 430 ). The predetermined temperature range may vary depending on the environment of use, from several tens of Celsius degrees to several hundreds of Celsius degrees. When the lamp  151   a  is used in the laser printer as a heat generator, for example, the predetermined temperature may be 80° C.˜140° C. in stand-by mode, and 170° C.˜200° C. in the printing mode.  
         [0051]     Hardware to support the above described method may be general hardware that is usually provided in the lamp driving equipment. That is, in the appliance having a lamp as the heat generator, a sensor to detect the temperature of the lamp and a processor to control the pulse-type electric current, which is applied to the lamp in accordance with the result of the sensor detection, are usually provided. As a result, the lamp control method according to the present invention does not require additional hardware to reduce an inrush of current to the lamp.  
         [0052]     Next, zero-crossing or phase control methods are operated to switch the power supply to the lamp and maintain the lamp at a predetermined temperature when power-off time exceeds a predetermined time such as 500 ms ( 440 ). As such, a half wavelength pulse is applied to the lamp to continue the driving of the lamp. Otherwise the method reverts to operation  430  in which the pulse-type electric current to the lamp is switched so as to maintain the temperature of the lamp at a predetermined degree.  
         [0053]     As a result, minimizing an inrush of current, which is generated in an electronic appliance employing a lamp as a heating element, is possible without a need to use separate hardware. In particular, when a lamp is used as a heating element in the aforementioned control method in an electronic appliance, such as a printer, a facsimile, a composite machine, or the like, a reduction of an inrush of current, which may be generated in the course of maintaining the temperature of a fixing device of the electronic appliance at a predetermined temperature in the stand-by state of the electronic appliance, is possible by programming the appliance in such a manner that half wavelength pulses are applied at predetermined time intervals and for a certain time during which, under the control on the temperature of the fixing device, the predetermined electric current to the lamp is cut off. According to an embodiment of the invention, for the certain time may be 300 ms after the turn-off of the lamp.  
         [0054]     Although a few 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 these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.