JP2011186389A - Image forming apparatus and control method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, etc. capable of suppressing the occurrence of a harmonic current and the occurrence of a beat sound of a coil by reducing the time for performing phase control, while suppressing a flicker. <P>SOLUTION: In the image forming apparatus for heat-fixing a toner image on a paper by using a fixing roller heated by a fixing roller heating means to which a current is supplied to generate heat, when the difference of power values supplied to the fixing roller heating means at a plurality of times in the past is within a predetermined range, a control means controlling the supply of the current to the fixing roller heating means controls the supply of the current in such a manner that the control period of cut-off control is prolonged so as to supply the power value supplied at the last time to the fixing roller heating means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for controlling heating to a fixing roller that heat-fixes a toner image on a sheet.

  In an electrophotographic image forming apparatus, a fixing roller used when fixing a toner image transferred onto a sheet by heat is heated by a heater (hereinafter referred to as “fixing heater”) heated by energization. Fixing heaters that use halogen lamps or the like as a heat source have positive resistance to temperature, so a large amount of power is required for heating by energization, and the temperature is high if the supplied voltage is constant Inrush current tends to be small, but a large inrush current flows when the temperature is low. This large inrush current causes voltage fluctuations in the power supply line to which a device equipped with the fixing device is connected, for example, flickering of an indoor fluorescent lamp (hereinafter referred to as “flicker”).

Therefore, a technique for suppressing the generation of such a large inrush current is already known.
Patent Document 1 discloses a technique relating to an electrophotographic apparatus including a fixing roller having a fixing heater that generates heat by controlling energization from an AC power source, and temperature detecting means for detecting the temperature of the fixing heater that heats the fixing roller. Has been. The configuration is calculated by a calculation means that calculates a resistance value of the fixing heater based on the detected temperature of the fixing heater, and obtains a control voltage value at which a predetermined current flows at the calculated resistance value. And a control means for controlling energization to the fixing heater according to the set control voltage value. When starting energization to the fixing heater, the control means corresponds to the control voltage. During the energization control, soft start-on control is performed to increase the energization phase angle every 1 Hz, and when the energization to the fixing heater is turned off, the control means energizes the energization by decreasing the energization phase angle every 1 Hz. Perform soft stop-off control. With this configuration, harmonic current and power supply voltage fluctuations are suppressed when the fixing heater is turned on and off.

  That is, in Patent Document 1, when the temperature is low, the current supplied to the fixing heater is limited by reducing the supply voltage, and the voltage supplied to the fixing heater is gradually increased by phase control. The inrush current generated at the initial stage when supplying the current to the terminal is suppressed to make it difficult for flicker to occur. The phase control refers to control for gradually increasing the current flowing to the fixing heater when supplying the current to the fixing heater.

  In recent years, a thin fixing roll having a small heat capacity may be used. However, the thin fixing roll having a small heat capacity can quickly reach the target temperature, while the temperature change with respect to the energization time is large. Therefore, temperature overshoot may occur due to environmental changes such as air temperature and humidity, and the temperature difference in the roll axis direction may increase. Therefore, during the heating period of the fixing heater where the surface temperature of the fixing roller reaches the target temperature upper limit value to the target temperature upper limit value, the fixing heater is forcibly energized with a very short control period (generally 1 second or less). Cut-off control is performed to turn on and off (see FIG. 4). As a result, fine power supply is performed, and the temperature overshoot of the fixing roll and the temperature difference in the fixing roller axial direction can be reduced.

  There is also a control method in which this cut-off control is combined with the soft start disclosed in Patent Document 1 described above. In cut-off control that repeatedly turns on and off in a short time, the phase control is repeated for the same period each time the fixing heater is turned on, so the total time during which the phase control is performed becomes longer. Will become bigger. And since an alternating current waveform will be greatly distorted by phase control, it will become easy to generate a harmonic current. The harmonic current generated thereby may cause a malfunction of the peripheral device or the power supply system. Further, since the cut-off control is repeatedly turned on and off in a short time, there has been a problem that a beat sound of the coil is generated in accordance with the turn-on and turn-off timing.

  Therefore, in Patent Document 2, in order to suppress the generation of the harmonic current and the beat sound of the coil, the control device performs the above phase control for the fixing heater, and the above-described very short in the cut-off control. Among the control cycles, a technique is disclosed in which the time for performing the phase control in the first control cycle within the heating period is lengthened and the control is performed differently from the time for performing the phase control in the second and subsequent control cycles within the heating period. ing.

  However, with the control device disclosed in Patent Document 2, the time for performing phase control in the first control cycle in the heating period is lengthened, and the time for performing phase control in the second and subsequent control cycles in the heating period is In the case of differentiating, it has been difficult to sufficiently shorten the total time during which the phase control is performed and to lengthen the control cycle of the cutoff control. In addition, since phase control is performed in the second and subsequent control cycles within the heating period, separately from the risk of generating harmonics and coiling noise during phase control in the first control cycle within the heating period. There is always a risk of the generation of harmonics during the phase control in the second and subsequent control cycles within the heating period, and the generation of coil beat noise. For this reason, there has been a limit in suppressing the generation of harmonic currents and the generation of coiling noise while suppressing flicker.

  An object of the present invention is to provide an image forming apparatus and an image forming apparatus control method capable of suppressing generation of harmonic current and generation of coil beat noise by reducing time for performing phase control while suppressing flicker. It is to provide.

  The invention according to claim 1 is an image forming apparatus that heat-fixes a toner image on a sheet using a fixing roller heated by a fixing roller heating means that generates heat when supplied with an electric current, and the surface temperature of the fixing roller is adjusted. Temperature detecting means for detecting, control means for controlling the supply of current to the fixing roller heating means so that the surface temperature detected by the temperature detecting means is within a predetermined range, and control data by the control means are stored in the storage unit Control data storage means for storing and determination means for determining whether or not the difference between the power values supplied to the fixing roller heating means based on a plurality of past control data stored in the storage unit is within a predetermined range When the determination means determines that the value is within the predetermined range, the control means adjusts the power value supplied to the fixing roller heating means so that the power value supplied most recently is supplied to the fixing roller heating means. An image forming apparatus, characterized in that by extending the control cycle-off control for controlling the supply of current.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when the determination unit determines that the value is within the predetermined range, the control unit further extends the total lighting time of the fixing roller heating unit and sets it longer. It is characterized by doing.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the determination unit determines that the value is within the predetermined range, the control unit further changes the execution time of the phase control. And

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, when the determination unit determines that the value is not within the predetermined range, the control unit is the latest in a plurality of past times. The current supply is controlled without extending the control period of the cutoff control of the first time.

  According to a fifth aspect of the present invention, there is provided a control method for an image forming apparatus in which a toner image is heated and fixed on a sheet by using a fixing roller heated by a fixing roller heating unit that generates heat when supplied with an electric current, the temperature detecting unit Detecting the surface temperature of the fixing roller by the control means, controlling the supply of current to the fixing roller heating means by the control means so that the surface temperature detected by the temperature detecting means falls within a predetermined range, and control data The difference between the power value supplied to the fixing roller heating unit based on a plurality of past control data stored in the storage unit by the determination unit and the control data stored in the storage unit by the determination unit is predetermined. A step of determining whether or not it is within a predetermined range, and when the determination means determines that it is within the predetermined range, the control means A method of controlling an image forming apparatus characterized by controlling the supply of current by extending the control cycle of the cut-off control, as supplied electric power values in time is supplied to the fixing roller heating means.

  According to a sixth aspect of the present invention, in the control method for the image forming apparatus according to the fifth aspect, when the determination means determines that it is within the predetermined range, the control means further extends the total lighting time of the fixing roller heating means. It is characterized by setting it long.

  According to a seventh aspect of the present invention, in the control method for an image forming apparatus according to the fifth or sixth aspect, the control unit further changes the execution time of the phase control when the determination unit determines that it is within the predetermined range. It is characterized by that.

  According to an eighth aspect of the present invention, in the method for controlling an image forming apparatus according to any one of the fifth to seventh aspects, when the determination unit determines that the value is not within the predetermined range, the control unit performs the past multiple times. The supply of current is controlled without extending the control cycle of the most recent cut-off control.

  According to the present invention, it is possible to reduce the time for performing phase control while suppressing flicker, thereby suppressing the generation of harmonic currents and the generation of beat sound of coils.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a hardware configuration related to control of a fixing heater that heats a fixing roller in an embodiment of the present invention. 1 is a functional block diagram of an image forming apparatus in an embodiment of the present invention. It is a figure explaining Duty of fixing heater 202 in an embodiment of the invention. 3 is a flowchart showing a control operation of the image forming apparatus in the embodiment of the present invention.

Embodiments of the present invention will be described below.
FIG. 1 is a diagram illustrating the overall configuration of the image forming apparatus according to the present embodiment.

  As shown in FIG. 1, the image forming apparatus according to the present embodiment has a configuration in which image forming portions (6Bk, 6M, 6C, 6Y) of respective colors are arranged along the transfer belt 5, and so-called It is said to be a tandem type.

  In FIG. 1, the transfer belt 5 rotates counterclockwise, and a plurality of image forming units (electrophotographic process units) 6Bk, 6M, 6C, 6Y are arranged in order from the upstream side in the rotation direction. The plurality of image forming units 6Bk, 6M, 6C, and 6Y have the same internal configuration except for the color of the toner image to be formed. The image forming unit 6Bk forms a black image, the image forming unit 6M forms a magenta image, the image forming unit 6C forms a cyan image, and the image forming unit 6Y forms a yellow image.

  In the following description, the image forming unit 6Bk will be described in detail. However, since the other image forming units 6M, 6C, and 6Y are the same as the image forming unit 6Bk, each configuration of the image forming units 6M, 6C, and 6Y is described. Regarding the elements, only the symbols distinguished by M, C, and Y are displayed in the drawing instead of Bk attached to each component of the image forming unit 6Bk, and the description thereof is omitted.

  The transfer belt 5 is an endless belt wound around a secondary transfer drive roller 7 and a transfer belt tension roller 8 that are rotationally driven. The secondary transfer drive roller 7 is driven to rotate by a drive motor (not shown), and the drive motor, the secondary transfer drive roller 7 and the transfer belt tension roller 8 serve as drive means for moving the transfer belt 5. Function.

  The image forming unit 6Bk includes a photoconductor 9Bk as a photoconductor, a charger 10Bk arranged around the photoconductor 9Bk, an exposure device 11, a developing device 12Bk, a cleaner blade 13Bk, and the like. The exposure device 11 is configured to irradiate laser beams 14Bk, 14M, 14C, and 14Y that are exposure beams corresponding to image colors formed by the image forming units 6Bk, 6M, 6C, and 6Y.

  At the time of image formation, the outer peripheral surface of the photoreceptor 9Bk is uniformly charged in the dark by the charger 10Bk, and then exposed from the exposure device 11 with the laser beam 14Bk corresponding to the black image, thereby forming an electrostatic latent image. The The developing device 12Bk visualizes the electrostatic latent image with black toner, thereby forming a black toner image on the photoreceptor 9Bk.

  This toner image is transferred onto the transfer belt 5 by the action of the primary transfer roller 15Bk at a position (primary transfer position) where the photoconductor 9Bk and the transfer belt 5 are in contact with each other. By this transfer, an image of black toner is formed on the transfer belt 5. After the transfer of the toner image, the photosensitive member 9Bk waits for the next image formation after the unnecessary toner remaining on the outer peripheral surface is wiped off by the cleaning blade 13Bk.

  As described above, the transfer belt 5 to which the black toner image is transferred by the image forming unit 6Bk is conveyed to the next image forming unit 6M by the transfer belt 5. In the image forming unit 6M, a magenta toner image is formed on the photoreceptor 9M by a process similar to the image forming process in the image forming unit 6Bk, and the toner image is superimposed on the black image formed on the transfer belt 5. And is transcribed.

  The transfer belt 5 is further conveyed to the next image forming units 6C and 6Y, and a cyan toner image formed on the photoconductor 9C and a yellow toner image formed on the photoconductor 9Y by the same operation. Are superimposed and transferred onto the transfer belt. Thus, a full-color image is formed on the transfer belt 5. The transfer belt 5 on which the full-color superimposed image is formed is conveyed to the position of the secondary transfer roller 16.

  In the image formation, in the case of printing only with black, the primary transfer rollers 15M, 15C, and 15Y are retracted to positions separated from the photoreceptors 9M, 9C, and 9Y, respectively, and the above-described image forming process is performed only for black. .

  During the paper transport operation during image formation, the paper 4 stored in the paper feed tray 1 is sequentially sent out by rotating the paper feed roller 2 counterclockwise from the top, and at the registration roller 3 position. stand by. The driving of the registration roller 3 is started at a timing at which the toner image and the position of the paper 4 overlap on the toner image conveyed by the transfer belt 5 and the secondary transfer roller 16. At this time, the registration roller 3 is rotated counterclockwise to feed out the paper 4.

  The paper 4 sent out by the registration roller 3 is transferred by a secondary transfer roller 16 to a toner image on the transfer belt 5 and then transferred by a fixing roller 203 (not shown) of the fixing device 17 described later. The toner image is fixed by heat and pressure, and is discharged to the outside of the image forming apparatus by a discharge roller 18 driven to rotate counterclockwise.

  When performing double-sided printing, the paper discharge roller 18 is driven to rotate clockwise before the paper 4 passes through the paper discharge roller 18 to convey the paper 4 to the double-sided conveyance path. The sheet 4 conveyed to the duplex conveyance path is conveyed again to the registration roller 3 via the duplex roller 19. The sheet 4 that has reached the registration roller 3 is again fed from the registration roller 3, and after the toner image is transferred to the opposite side of the sheet surface by the secondary transfer roller 16, a fixing roller described later of the fixing device 17. The toner image transferred at 203 (not shown) is fixed by heat and pressure, and discharged to the outside of the image forming apparatus by a discharge roller 18 driven to rotate counterclockwise.

  FIG. 2 is a diagram illustrating a hardware configuration related to control of a fixing heater that heats the fixing roller in the present embodiment.

  As shown in FIG. 2, an AC power supply is used as a heater power supply 201 having a coil inside the power supply, and power is supplied to a fixing heater 202 using a halogen lamp or the like as a heat source via a switching element 206. The switching element 206 may be a high-speed switching element such as a semiconductor switching element, a transistor, a thyristor, or a triac.

  The temperature of the fixing heater 202 is detected by the temperature detection circuit 205 to which the output of the temperature thermistor 204 provided near the fixing heater 202 is input. The zero-cross circuit 208 is for detecting the zero-cross point of the heater power supply 201, and a control signal is output to the switching element 206 in order to control the phase of the current supplied to the fixing heater 202 by the CPU 207. Generally, when the time from the zero cross point to the heater on is set long, the energization time to the fixing heater 202 is shortened. Conversely, if the time from the zero cross point to the heater ON is set short, the energization time to the fixing heater 202 becomes long and the amount of heat given to the fixing roller 203 becomes large. The fixing heater 202, the fixing roller 203, the temperature thermistor 204, and the temperature detection circuit 205 may constitute the fixing device 17 shown in FIG.

  In addition, when supplying current to the fixing heater 202, cut-off control for forcibly turning on and off the energization is repeatedly performed at a predetermined control period stored in the memory 209, and the surface temperature of the fixing roller 203 is set to the target temperature. When it is detected that the upper limit value is exceeded, the heating control of the fixing heater 202 is terminated. Specifically, the surface temperature of the fixing roller 203 is periodically detected by the temperature thermistor 204 when the job of the image forming apparatus is waiting, and the output from the temperature thermistor 204 is detected by the temperature detection circuit 205, and the fixing roller 203 is detected. Is lower than the target temperature lower limit value stored in the memory 209, the CPU 207 performs heating control by energizing the fixing heater 202, while the surface temperature of the fixing roller 203 is stored in the memory 209. When the target temperature upper limit value is exceeded, the CPU 207 performs control to stop energization of the fixing heater 202, so that the surface temperature of the fixing roller 203 heated by the fixing heater 202 is controlled within a certain temperature range. .

FIG. 3 is a functional block diagram of the image forming apparatus according to the present embodiment.
The image forming apparatus according to the present embodiment includes a fixing roller heating unit 301, a temperature detection unit 302, a heating control number determination unit 303, a power value determination unit 304, a control unit 305, a control data storage unit 306, and a storage unit 307.

  The fixing roller heating unit 301 has a function of heating the fixing roller 203. It may be realized by the fixing heater 202 using a halogen lamp or the like as a heat source.

  The temperature detection unit 302 has a function of detecting the temperature of the fixing heater 202. The temperature thermistor 204 provided near the fixing heater 202 and detecting the surface temperature of the fixing roller 203 and the temperature detection circuit 205 to which the output of the temperature thermistor 204 is input may be realized. The detected temperature information may be passed from the temperature detection circuit 205 to the CPU 207.

  The heating control frequency determination unit 303 has a function of determining the heating control frequency with reference to the storage unit 307 that stores the number of times that the heating control by energization of the fixing heater 202 is performed. It may be realized by the CPU 207. Note that the execution of the heating control means from the start of the heating control by the control unit 305 to the end thereof. When the heating control is completed, it is counted as one and the number of times is incremented by one.

  The power value determination unit 304 calculates and calculates the power value given to the fixing heater in the predetermined control cycle stored in the storage unit 307 for the past predetermined number of times of heating control by energizing the fixing heater 202. It is determined with reference to the storage unit 307 that stores the numerical values related to the past heating control and the certain constant value whether or not the difference between the respective electric power values is not more than a certain certain value (threshold value). It has a function. As for the power value, the temperature detected by the temperature detection unit 301 at a predetermined time and the current value applied to the fixing heater 202 stored in the storage unit 307 by the control data storage unit 306 at each time of the past heating control. The power value given to the fixing heater 202 by one heating control is calculated on the basis of the information on the time when the heating control is performed. It may be realized by the CPU 207. In addition, that the difference of electric power value is below a certain fixed value (threshold value) means that the electric power value used for the heating control for the past predetermined number of times is substantially the same. Furthermore, the fact that the power values used for heating control for a predetermined number of times in the past are approximately the same may mean that there are few fluctuations in the environment such as air temperature and humidity during that time.

  The control unit 305 has a function for controlling the entire image forming apparatus. In the heating control by energizing the fixing heater 202, not only the start / end of the heating control but also the control cycle is changed in a predetermined case, the total lighting time of the fixing heater 202 is lengthened and the phase control is performed. Control to change the time. It may be realized by the CPU 207.

  The control data storage unit 306 associates the temperature detected by the temperature detection unit 301 at a predetermined time in the control cycle for each heating control by the control unit 305 with the current value applied to the fixing heater 202, and In addition, the storage unit 307 has a function of storing the time when overheating is performed for each heating control by the control unit 305. It may be realized by the CPU 207.

  The storage unit 307 has a function of storing various data and threshold values. It may be realized by the memory 209.

FIG. 4 is a diagram for explaining the duty of the fixing heater 202 controlled by the control unit 305 of the image forming apparatus according to the present embodiment.
The fixing heater DUTY (A) in FIG. 4 is a conventional control method, and the fixing heater DUTY (B) shows a control example in the present embodiment.

Referring to FIG. 4, in the control example in the present embodiment, first, as described above, when supplying current to fixing heater 202 as in the conventional control method, control cycle T stored in storage unit 307 is stored. Cut-off control is performed to forcibly turn on and off the power.
The control unit 305 turns on the energization of the fixing heater 202 and shifts (starts) to heating control by energization, and sequentially performs the phase control soft start t1, the full lighting t2, and the phase control soft stop t3 in order. After that, the current supply to the fixing heater 202 is forcibly stopped only for the remaining time of the control cycle T, which is the OFF time of the cutoff control.
When the temperature of the fixing heater 202 detected by the temperature detection unit 302 exceeds the target temperature upper limit value stored in the storage unit 307, the control unit 305 turns off the energization of the fixing heater 202 and performs heating control. finish.

After performing the above heating control N times (N is an arbitrary integer equal to or greater than 2), the power value determination unit 304 performs the past M of the heating control by energizing the fixing heater 202 at the (N + 1) th and subsequent heating control transitions. The batch (M is an arbitrary integer equal to or greater than 2 above N) (here, the N-1th and Nth times) is given to the fixing heater in the control cycle T stored in the storage unit 307. Each power value is calculated, whether or not the difference between the calculated power values is less than a certain value (threshold value), the numerical value related to the past heating control and the power value of the certain constant value are stored. This is determined with reference to the storage unit 307.
When the difference between the calculated (N−1) th power value and the Nth power value is equal to or smaller than a predetermined constant value, the N + 1th calculated power value immediately before the (N + 1) th time is heated to the (N + 1) th heating. The control unit 305 changes and sets the control cycle T to be extended to the control cycle nT so as to be given to the fixing heater 202 at the time of control. carry out. In this case, the phase control soft start t1 and soft stop t3 may be shortened to set the optimum length.

Since the control cycle T can be changed to the control cycle nT, an optimal amount of heat can be given to the fixing roller 203 by giving an appropriate power value to the fixing heater 202 without depending on the fixed control cycle T, and By changing and setting the control cycle T to be extended to the control cycle nT, the total time of the soft start t1 and the soft stop t3 of the phase control can be shortened. In FIG. 4, the control cycle T is extended to the control cycle nT, and in the conventional control method, the soft start t <b> 1 and the soft stop t <b> 3 are generated three times. In the control example in the present embodiment, The soft start t1 and the soft stop t3 of the phase control are performed once, the total time of the soft start t1 and the soft stop t3 of the phase control is shortened, and the time average value of the harmonic current is reduced. Furthermore, in the conventional control method, the phase control is performed three times. However, in the control example in the present embodiment, since the phase control is performed once, the second and subsequent phase control in the control cycle T of the conventional control method is performed. There is no risk of generation of harmonics of time or generation of beat sound of coils.
Thereby, generation | occurrence | production of a harmonic current and generation | occurrence | production of the beat sound of a coil can be suppressed, suppressing a flicker.

Hereinafter, the control operation of the image forming apparatus according to the present embodiment will be described in detail with reference to the flowchart of FIG.
The image forming apparatus is premised on the transition to the standby state from each mode, such as standby transition after completion of warm-up, standby transition after completion of printing, and standby transition after returning from sleep.

  The temperature detection circuit 205 provided in the vicinity of the fixing heater 202 and inputted with the output of the temperature thermistor 204 for detecting the surface temperature of the fixing roller 203 falls below the target lower limit value stored in the memory 209. When the control unit 305 detects this, the control unit 305 starts the heating control by energizing the fixing heater 202. First, the heating control number determination unit 303 determines the number of times the heating control by energizing the fixing heater 202 is performed. It is determined with reference to the stored storage unit 307 whether or not the number of times of heating control is N times (N is an arbitrary integer equal to or greater than 2) (step S1).

  When it is less than N times (step S1 / NO), the control unit 305, for example, as shown in FIG. t2 and phase control soft stop t3 are sequentially performed, and heating control is performed by energizing the fixing heater 202 (step S2). The control data storage unit 306 associates the temperature detected by the temperature detection unit 301 at a predetermined time in the control cycle T for the current heating control by the control unit 305 with the current value applied to the fixing heater 202. In addition, the storage unit 307 stores the time over which the control unit 305 performs overheating for the current heating control.

  On the other hand, when it is N times or more (step S1 / YES), the power value determination unit 304 is the past M times of heating control by energizing the fixing heater 202 (M is an arbitrary integer equal to or greater than 2 above N). Here, the difference between the power values calculated by calculating the power value given to the fixing heater in the predetermined control cycle stored in the storage unit 307 for the N-1th time and the Nth time for two times. Whether or not is less than a certain value (threshold value) is determined with reference to the storage unit 307 storing the numerical values related to the past heating control and the certain value (step S3). As for the power value, the temperature detected by the temperature detection unit 301 and the current value applied to the fixing heater 202 at a predetermined time stored in the storage unit 307 by the control data storage unit 306 in each past heating control. Based on the information regarding the heating time, the power value given to the fixing heater 202 by one heating control is calculated.

  If it exceeds the certain fixed value (threshold value) (step S3 / NO), the process proceeds to step S2. Note that a difference in power value exceeding a certain value (threshold value) means that the power values used for the past M heating controls differ considerably. Furthermore, the fact that the power values used for the past M times of heating control differ considerably may suggest that there may be large environmental fluctuations such as air temperature and humidity during that time. Therefore, the control cycle T or the like is not changed.

  On the other hand, when the value is equal to or less than the above certain value (threshold value) (step S3 / YES), the control unit 305 uses the N + 1 calculated power value immediately before the (N + 1) th time when the N + 1th heating control is performed. In order to give an optimum amount of heat to the fixing roller 203, for example, as shown in FIG. Regarding the control soft stop t3, the control cycle T is changed and set to extend to the control cycle nT, and the heating control is performed after the time of all lighting t2 is extended and set longer (step S4). At this time, the phase control soft start t1 and soft stop t3 may be shortened to set the optimum length. Change data such as the control period, the time of all lighting t2 and the time of phase control are stored in the storage unit 307. In addition, that the difference of electric power value is below a certain fixed value (threshold value) means that the electric power value used for the past M heating control is substantially the same. Furthermore, the fact that the power values used for the past M times of heating control are approximately the same may suggest the possibility that there are few fluctuations in the environment such as air temperature and humidity during that time. Therefore, it is determined that there is little risk of temperature overshoot due to environmental fluctuations such as air temperature and humidity, or a temperature difference in the roll axis direction becoming large, and the control cycle T is extended to the control cycle nT. It can be changed and set so that the time of full lighting t2 can be extended and set longer.

  Further, a temperature thermistor 204 that detects the surface temperature of the fixing roller 203 provided in the vicinity of the fixing heater 202 by repeatedly performing cut-off control forcibly turning on and off the energization with the control cycle nT stored in the storage unit 307. When the temperature detection circuit 205 that receives the output of the output detects that the surface temperature of the fixing roller 203 has exceeded the target temperature upper limit value stored in the memory 209, the control unit 305 stops energizing the fixing heater 202. Then, the heating control is finished (step S5). Thereby, the surface temperature of the fixing roller 203 heated by the fixing heater 202 is controlled within a certain temperature range (within the range between the target temperature upper limit value and the target temperature lower limit value). The control data storage unit 306 associates the temperature and current value detected by the temperature detection unit 301 applied to the fixing heater 202 at a predetermined time in the control cycle nT for the current heating control by the control unit 305. In addition, the storage unit 307 stores the time over which the control unit 305 performs overheating for the current heating control.

  Each embodiment described above is a preferred embodiment of the present invention, and various modifications can be made without departing from the gist of the present invention. For example, a process for realizing the function of the image forming apparatus may be performed by causing the image forming apparatus to read and execute a program for realizing the function of the image forming apparatus. Further, the program is transmitted to another computer system by a transmission wave via a computer-readable recording medium such as a CD-ROM or a magneto-optical disk, or via a transmission medium such as the Internet or a telephone line. Also good.

DESCRIPTION OF SYMBOLS 1 Paper feed tray 2 Paper feed roller 3 Registration roller 4 Paper 5 Transfer belt 6Bk, 6M, 6C, 6Y Image formation part 7 Secondary transfer drive roller 8 Transfer belt tension roller 9Bk, 9M, 9C, 9Y Photoconductor 10Bk, 10M, 10C, 10Y charger 11 Exposing device 12Bk, 12M, 12C, 12Y Developer 13Bk, 13M, 13C, 13Y Cleaner blade 14Bk, 14M, 14C, 14Y Laser light 15Bk, 15M, 15C, 15Y Primary transfer roller 16 Secondary transfer roller DESCRIPTION OF SYMBOLS 17 Fixing device 18 Paper discharge roller 201 Heater power supply 202 Fixing heater 203 Fixing roller 204 Temperature thermistor 205 Temperature detection circuit 206 Switching element 207 CPU
208 Zero cross circuit

JP-A-10-091037 JP 2006-351400 A

Claims (8)

An image forming apparatus that heats and fixes a toner image on a sheet using a fixing roller heated by a fixing roller heating unit that generates heat when supplied with an electric current,
Temperature detecting means for detecting the surface temperature of the fixing roller;
Control means for controlling the supply of current to the fixing roller heating means so that the surface temperature detected by the temperature detection means falls within a predetermined range;
Control data storage means for storing control data by the control means in a storage unit;
Determining means for determining whether or not a difference in power value supplied to the fixing roller heating means based on a plurality of past control data stored in the storage unit is within a predetermined range;
When the determination unit determines that the value is within the predetermined range, the control unit cuts the power value supplied to the fixing roller heating unit in the most recent time among the plurality of past times. An image forming apparatus, wherein a current supply is controlled by extending a control period of off control.   The image forming apparatus according to claim 1, wherein when the determination unit determines that the value is within the predetermined range, the control unit further extends the total lighting time of the fixing roller heating unit to set a longer time.   3. The image forming apparatus according to claim 1, wherein when the determination unit determines that the phase is within the predetermined range, the control unit further changes a phase control execution time. 4.   When it is determined by the determination means that it is not within the predetermined range, the control means controls the supply of current without extending the control cycle of the most recent cut-off control among the plurality of past times. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A control method for an image forming apparatus that heat-fixes a toner image on a sheet using a fixing roller heated by a fixing roller heating unit that generates heat when supplied with an electric current,
Detecting the surface temperature of the fixing roller by a temperature detecting means;
Controlling the supply of current to the fixing roller heating means by the control means so that the surface temperature detected by the temperature detection means falls within a predetermined range;
Storing control data by the control means in a storage unit by a control data storage means;
Determining whether or not the difference between the power values supplied to the fixing roller heating unit based on a plurality of past control data stored in the storage unit by the determination unit is within a predetermined range. ,
When the determination unit determines that the value is within the predetermined range, the control unit cuts the power value supplied to the fixing roller heating unit in the most recent time among the plurality of past times. A control method for an image forming apparatus, wherein the supply of current is controlled by extending a control cycle of off control.   The image forming apparatus according to claim 5, wherein when the determination unit determines that the value is within the predetermined range, the control unit further extends the total lighting time of the fixing roller heating unit to set a longer time. Control method.   7. The method of controlling an image forming apparatus according to claim 5, wherein when the determination unit determines that the phase is within the predetermined range, the control unit further changes a phase control execution time.   When it is determined by the determination means that it is not within the predetermined range, the control means controls the supply of current without extending the control cycle of the most recent cut-off control among the plurality of past times. The method for controlling an image forming apparatus according to claim 5, wherein the image forming apparatus is a control method.

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