JPH1173057A - Image forming device, image forming method and storage medium storing image forming procedure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the fluctuation of current consumption of the whole of a device so as to lower the influence to a power supply equipment provided out of a device by including plural heaters in a fixing unit, switching each heater with current switching elements a high frequency, performing the PWM control to the current flowing in a heater so as to control the calorific value of the all heaters at a desirable value, and controlling the ON-timing of the PWM control signal for controlling each heater per each heater. SOLUTION: Temperature of heaters is detected by a sensor 5, and time for turning a switching element on is changed in response to the detected temperature so as to control the current to be flowed to the heaters. Two heaters are connected in parallel with each other, and connected to a switching element for controlling the current to be electrified to each heater (A), (B). A CPU 105a outputs the heater control signal (A), (B) as a signal for controlling the switching elements (A), (B).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus, an image forming method, and a storage medium storing an image forming procedure.

More specifically, the present invention stores an image forming apparatus, an image forming method, and an image forming procedure which appropriately control power supply to a fixing heater when forming an image using an electrophotographic process. It relates to a storage medium that has been used.

[0003]

2. Description of the Related Art FIG. 15 is a sectional view showing an example of this type of image forming apparatus, for example, a laser beam printer. In FIG. 1, reference numeral 100 denotes a controller unit, which converts an electric signal, which is code data, input from a host computer (not shown) into
In step 3, the image is developed into a dot image, stored in the memory inside the video controller, and returned to the engine unit 202 as a video signal.

[0004] Each element of the engine unit 202 is controlled by an engine controller 205, and the controller unit 10
Exchanging video signals with the engine controller 2
05. A video signal input to a video interface unit (not shown) of the engine controller 205 is sent to the laser driver 106, where ON / OFF of the semiconductor laser 107 is controlled. A laser beam 110 emitted from the semiconductor laser 107 is deflected by a polygon mirror 108 to form a photosensitive drum 112.
, And is projected on the photosensitive drum 112 via the mirror 109. The photosensitive drum 112 rotates in the direction of the arrow and is primarily charged by the primary charger 111, and then receives an exposure corresponding to ON / OFF of the laser beam to form an electrostatic latent image on the surface of the photosensitive drum. Then, after colored toner particles (hereinafter, referred to as toner) are applied by the developing device 113 and a visible image is obtained, the recording is taken out one by one from the paper feeding cassette 120 by the transfer charging device 114 by the paper feeding roller 121. The above visual image is transferred to a medium.
The transfer residual toner is wiped off from the surface of the photosensitive drum 112 by the cleaning device 115, and the photosensitive drum 112 prepares for the next image forming process.

On the other hand, the recording medium on which the unfixed toner image is placed is inserted into the fixing device 116, and after a permanent fixed image is obtained, the recording medium is discharged out of the apparatus as a final print in the direction of the arrow in the figure. The arrows in the figure indicate the feeding trajectory of the recording medium taken out of the sheet cassette 120 and conveyed. The fixing device 116 has a heater (fixing heater) 219 in the hollow fixing roller 117. When a current is supplied to the heater 219, the fixing roller 117 is overheated, and a sensor (not shown) for detecting the surface temperature of the fixing roller 117 is provided. The output is input to a temperature controller (not shown), and the heater 219 is turned on / off to maintain a predetermined surface temperature. The pressure roller 118 is an urging means (not shown)
Is pressed by the fixing roller 117, and the unfixed toner on the recording medium is removed by the fixing roller 117 and the pressing roller 1.
The recording medium is heated and pressurized together with the recording medium in the nip formed by 18 to be permanently fixed.

[0006] The engine controller 205 includes a fixing device 1
The temperature of the fixing device 116 is determined by the temperature sensor 5 (FIG. 16) attached in contact with the 16 fixing rollers 117,
The fixing heater 219 is controlled using the fuser control unit 300 shown in FIG. 16 to control the temperature of the fixing device 116.

In FIG. 16, a fuser control unit 300
In addition, a temperature sensor 5 and a CPU (engine controller) 205 are also shown.

[0008]

However, in the above-described conventional example, the fluctuation of the current consumed by the image forming apparatus in controlling the heater is large, and the power supply equipment outside the apparatus is affected by the fluctuation of the voltage. There was a problem.

Accordingly, an object of the present invention is to provide
A plurality of heaters are included in the fixing device, each heater is switched using a current switching element, and the amount of heat generated by all the heaters is controlled to a desired value by controlling the current flowing through the heaters by PWM. An image forming apparatus, an image forming method, and an image forming method in which the ON timing of a PWM control signal to be controlled is controlled for each heater, thereby reducing the fluctuation of current consumed by the entire apparatus and reducing the influence on power supply equipment outside the apparatus. An object of the present invention is to provide a storage medium storing an image forming procedure.

[0010]

In order to solve the above-mentioned problems, according to the present invention, a plurality of heaters are controlled in heater control of a fixing device, and each heater is switched at a high frequency using a current switching element. In addition, the amount of heat generated by each heater is controlled to a desired value by performing PWM control on the current flowing through the heater, and the ON timing of a PWM control signal for controlling the heater is controlled for each heater.

That is, according to the present invention, in an image forming apparatus provided with a heater as a fixing unit for fixing a coloring material on a recording material, a plurality of heating elements used as the heater, and a detecting means for detecting a temperature of the heating element. Means, and control means for individually performing PWM driving of a current flowing through each of the heating elements in response to a detection output of the detection means.

According to another aspect of the present invention, there is provided an image forming apparatus including a plurality of heaters as fixing means for fixing a developing material to a recording medium, wherein a plurality of heaters for controlling a current flowing through the heaters connected in parallel are provided for each heater. Is provided.

In these inventions, it is possible to control so that the currents flowing through the heaters do not overlap.
When the number of the heaters is two, it is possible to control by shifting the phase of the signal for controlling each heater by a half cycle. Further, when the number of the heaters is three, the phase of the signal for controlling each heater is set to three.
It is possible to control by shifting by one-half cycle. When the number of the heaters is two, it is possible to perform control so that the ON timing of the control signal in the first heater and the OFF timing of the control signal in the second heater are simultaneously performed. Further, when the number of the heaters is two, the start of the ON timing of the control signal in the first heater and the start of the OFF timing of the control signal in the second heater are set to the same timing, and The end of the OFF timing of the control signal in the second heater and the OFF of the control signal in the second heater.
It is possible to control so that the timing ends at the same timing. Further, it is possible to control the heating value of each of the heaters to be equal.
Further, when raising the temperature of the fixing unit from room temperature to a temperature at which the fixing can be performed, the currents flowing through the plurality of heaters are controlled so as to overlap each other. When performing the fixing control of the medium, it is possible to perform control so that the currents of the plurality of heaters do not overlap.

In the image forming method according to the present invention, when a developer is fixed on a recording medium using a fixing device having a plurality of heaters, the current flowing through the heater having the plurality of heaters is individually controlled. PWM control.

Further, when a developer is fixed on a recording medium by using a fixing device having a plurality of heaters, currents flowing through the heaters having the plurality of heaters are individually subjected to PWM.
It is also possible to configure a storage medium in which the control procedure is stored in the form of a program.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 2 is a block diagram showing an electrical configuration of a laser beam printer to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a power switch, which is used to turn on / off the power of the image forming apparatus. Reference numeral 2 denotes a noise filter which reduces noise generated by the image forming apparatus so that the noise does not propagate to the AC line. Reference numeral 3 denotes a fuser control unit, which is used to detect the temperature of a fixing heater 119 serving as a heat source for performing heat fixing by the temperature sensor 5 and perform ON / OFF control so that the engine controller 105 keeps the temperature constant. .

4 is a low voltage power supply unit, 5 is a temperature sensor, 6 is a fan, 7 is a fan motor driver, 8 is a light receiving element, 9 is a BD circuit, 10 is a high voltage power supply, 11 is a scanner motor, and 12 is a scanner motor. Scanner motor driver, 13 is a main motor, 14 is a main motor driver, 15 is a paper size sensor, 16 is a paper presence sensor, 17 is a door sensor, 18 is a paper feed sensor, 19 is a paper ejection sensor, 20 is a cartridge sensor, and 21 is A video I / F circuit; 100, a video controller unit; 101, a host I / F circuit;
3 is a video controller, 103a is a CPU, 103b
Is RAM, 103c is ROM, 103d is buffer, 1
03f is a nonvolatile storage medium, 104 is an operation panel, 10
5 is an engine controller, 105a is a CPU, 105
b is a RAM, 105c is a ROM (control procedures are stored), 106 is a laser driver, 107 is a laser diode, 111 is a primary charger, 112 is a photosensitive drum, 11
3 is a developing device, 114 is a transfer charger, 116 is a fixing device, 1
19 is a fixing heater.

FIG. 1 is a circuit block diagram of a fuser control unit to which the present invention is applied. Here, the temperature of the heater is detected by the temperature sensor 5, and the current flowing through the heater is controlled by changing the ON time of the switching element according to the temperature. Two heaters are connected in parallel and each heater (A)
And (B) are connected to a switching element for controlling a current supplied thereto. Therefore, the CPU 105a outputs heater control signals (A) and (B) as signals for controlling the switching elements (A) and (B).

FIG. 3 is a diagram showing the relationship between the power supply voltage and the current waveform of the heater. The amount of power to the heater is calculated based on the temperature information detected by the temperature sensor 5 by the program in the CPU. The program outputs heater control signals (A) and (B) based on the calculated energization amount. The switching element of the fuser control unit controls so that a current that flows through the heater flows when the heater control signal is at the “high” level. The heater control signal (A) controls the switching element (A) to control the current supplied to the heater (A), and the heater control signal (B) controls the switching element (B) to supply the current to the heater (B). To control the current. The current supplied to both heaters has a waveform obtained by adding the current supplied to the heater (A) and the current supplied to the heater (B), as shown in FIG.

FIG. 4 is a diagram showing the relationship between the heater control signal and the voltage and current applied to the heater in a short time and showing the relationship more easily. FIG. 5 shows the relationship between the heater control signals (A) and (A).
It is the figure which showed the relationship of (B). In FIG. 5, the heater control signal (A) and the heater control signal (B) are controlled so as not to be turned on at the same time. That is, during the TA-OFF period of the heater control signal (A), the heater control signal (B)
Is turned on, and the heater control signal (A) is controlled to be turned on during the TB-OFF period of the heater control signal (B). Therefore, as shown in FIG. 4, the ripples of the individual currents of the heaters (A) and (B) are large, but the ripples of the current of the heater (A) + (B) obtained by combining the two currents are small. Therefore, the current supplied from the commercial power supply to the image forming apparatus has a current waveform that flows through both heaters.

By setting the switching frequency of the heater control signal to a sufficiently high frequency and adjusting the impedance of the inductor and the heater, the current waveform becomes close to a sine wave as shown in FIG. Further, since the frequency can be increased, the capacitance of the inductor can be set low.

(Embodiment 2) In the first embodiment, the heater control signal (A) and the heater control signal (B) are controlled so as not to overlap. However, as shown in FIG. ) And (B) are set to a half cycle (TA / 2).
The current waveform at this time is as shown in FIG. As shown in FIG. 8, the current waveform at the time when the heater control signals (A) and (B) overlap each other is shown in FIG.
The current flowing through + B has a waveform that is switched at twice the switching frequency of the heaters (A) and (B).

(Embodiment 3) FIG. 10 is a diagram showing the timing of a heater control signal according to a third embodiment. In the figure, the timing (tA-ON) at which the heater control signal (A) is turned on is determined by the heater control signal (B).
Control is performed so as to be performed simultaneously with the FF timing (tB-OFF). The timing for turning off the heater control signal (A) (tA-OFF) and the timing for turning on the heater control signal (B) (tB-ON) are as follows. Is determined by the ON time and the OFF time. Since the switching frequency is controlled to be constant, the cycle T is constant.

FIG. 11 is a diagram showing a waveform of a heater control signal when the power supply to the heater is increased.

The third embodiment has timers for the heater control signals (A) and (B) and another timer for controlling the phase difference between the heater control signals (A) and (B). The timer of the heater control signal (A) is tA-ON, t
The timing of A-OFF, T is set, and the heater control signal (A) is controlled. Similarly, the heater control signal (B) is controlled by the timer of the heater control signal (B). Then, after turning on the heater control signal (A), the heater control signal (B)
Is controlled by a timer for controlling the phase difference. This phase difference is obtained by converting the signal from the period (T) to O
N minus the period, ie, (T)-(tA-
From ON to tA-OFF).

(Embodiment 4) FIG. 12 is a timing chart of a heater control signal according to a fourth embodiment. In the figure, the heater control signal (A) turns on the heater in the Ton period and turns off the heater in the Toff period. Similarly, the heater control signal (B) turns on the heater in the Ton period,
The heater is turned off during the Toff period. Turn ON / O heater
Ton and Toff at the timing of performing FF are set by detecting the temperature of the heater and calculating the heat generation amount from the detected temperature.
The control signal is controlled by a timer based on the calculated value.

The heaters (A) and (B) are controlled so as not to be turned on / off at the same timing, and control signals are set as follows in order to omit the calculation of the timing. To turn on the heater control signal (A) for the Ton period, the timer (A) for generating the heater control signal (A) is set to Ton.
Set the time. At the same time, the heater control signal (B) is set to T
The time of Toff is set in the timer (B) for generating the heater control signal (B) to turn off the off period. As shown in the figure, at time t1, the heater control signal (A) is turned on and the heater control signal (B) is turned off. Next, at time t2, when the timer (A) for the ON time of the heater control signal (A) stops, the signal is turned off. The time of Toff is set in the timer (A) of the heater control signal (A).

Next, at time t3, when the timer (B) for the OFF time of the heater control signal (B) stops, the signal is turned on. The time of Ton is set in the timer (B) of the heater control signal (B).

Next, at time t4, the period T = Ton + Tof
Since f, the timer (A) in which the OFF time of the heater control signal (A) is set stops, and the timer (B) in which the ON time of the heater control signal (B) is set stops. The ON time is set in the timer (A) again and the OFF time is set in the timer (B) in the same manner as at the time t1. The heater control signal (A) is turned on, and the heater control signal (B) is turned off. This control is further repeated.

FIG. 13 is an example showing a case where t3 occurs before timing t2 in the above description, and the control method is the same as that described above.

In the fourth embodiment described above, the timings from t1 to t4 are calculated in advance, and control is performed by setting one timer after another.

In the third embodiment, three timers are required, but the control is simplified. On the other hand, in the fourth embodiment, only one timer is required, but the control is more complicated than in the third embodiment.

(Embodiment 5) FIG. 14 is a timing chart of a heater control signal according to a fifth embodiment. When controlling the amount of heat generated by combining a plurality of heaters, a difference in the amount of heat generated by the heater occurs due to a difference in resistance between the heaters. When a heater having only a resistor is considered, the voltage V, the heater resistance R1, R
Assuming that W is the power consumption when the resistors are connected in parallel and controlled as shown in FIG.

[0035]

W = V × V / (R1 × R1 / (R1 + R2)) (1), and the heat value of each heater is

[0036]

W1 = V × V / R1, W2 = V × V / R2 (2) Since the heaters are connected in parallel, the power supply voltage is the same for both heaters. The resistance of the heater is R1
= R2, so the calorific value is different.

[0037]

W 1 ３W 2 (where R 1 ≠ R 2) (3) Therefore, there is a difference in the amount of heat generated by the heater.

In order to absorb the difference in the amount of heat generated when a plurality of heaters are controlled simultaneously, the ON period of the heater control signal for turning on the heater is controlled by the heater control signals (A) and (A) as shown in FIG. Adjust the temperature in B) to keep the calorific value constant. In the same figure, the resistance of the heater (B) is larger than the resistance of the heater (A), so that the example of the heating value of the heater (B) is small. Therefore, the ON time TB-ON of the heater control signal (B) is made longer than the ON time TA-ON of the heater control signal (A) for controlling the heater (A), so that the heater (B)
Is adjusted so that the calorific value increases.

Means for detecting each heat generation amount are as follows: (a) When the resistance of the heater is measured at the time of shipment from the factory and stored in a non-volatile storage medium and the control is performed, the program of the CPU reads the information and sets the ON time. How to calculate.

(B) When the apparatus is started or when printing is started, power is supplied to each of the heaters at a constant ON duty, and the temperature change time is measured by the temperature detecting means to detect a deviation in the heat value of each heater. Method.

(C) A method in which a plurality of temperature detecting means are provided so that the temperature of each heater can be measured, the temperature of each heater is detected, and the ON duty of the heater control signal is adjusted so that the temperature becomes constant.

And so on.

(Embodiment 6) The heater control signal of Embodiment 5 is controlled as in Embodiment 1, but may be controlled in Embodiments 2, 3, and 4.

(Embodiment 7) Embodiments 1, 2, 3,
In 4, 5, and 6, control examples for two heaters are shown, but the present invention can be similarly applied when controlling three or more heaters.

(Eighth Embodiment) In the second embodiment,
When the heater current is less than 50%, the heater control signal (A) and the heater control signal (B) do not overlap each other, and the heater current does not overlap. Therefore,
Current fluctuation is small. In a state where the heater current is less than 50%, the resistance value of the heater is set so that the fixing control of the recording medium can be performed, and the temperature of the fixing device of the control requiring more heat generation is warmed from room temperature to a temperature at which fixing can be performed. The control is performed in a state where the heater current exceeds 50%.

(Embodiment 9) In Embodiment 8, the state where the heater control signal (A) and the heater control signal (B) do not overlap until the heater current is less than 50% has been described for simplicity. When the fixing control of the medium is performed, each heater control signal is controlled so as not to be simultaneously turned on at the same timing, and the rise from the room temperature to the temperature at which fixing can be performed may be simultaneously controlled in the ON state. It does not have to be fixed.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Needless to say, the present invention can be applied to a case where the present invention is achieved by supplying a program to a system or an apparatus. In this case, by reading a storage medium storing a program represented by software for achieving the present invention into the system or the apparatus, the system or the apparatus can enjoy the effects of the present invention. Becomes

[0048]

As described above, according to the present invention,
When controlling the heater of the fixing unit, a plurality of heaters are controlled, each heater is switched at a high frequency by using a current switching element, and the amount of heat generated by the entire heater is controlled to a desired value by performing PWM control on a current flowing through each heater. By controlling the ON timing of the PWM control signal for controlling each heater for each heater in addition to the control, the fluctuation of the current consumed by the entire apparatus can be reduced, and the influence on the power supply equipment outside the apparatus can be reduced.

Further, as described in the second embodiment, the switching frequency of the current of the entire heater can be doubled by shifting the phase of each heater control signal by a half cycle, so that the input of the heater can be doubled. The current ripple can be reduced, and the capacitance of the input inductor can be reduced.

Further, as shown in the fifth embodiment, by controlling the amount of heat generated by each heater to be constant, the temperature gradient in the fixing nip can be reduced, so that the image quality can be improved.

Further, as shown in the eighth and ninth embodiments, during the fixing control of the recording medium, the heater gradient is set so that the currents of the heaters do not overlap, so that the fluctuation of the current during the printing operation is reduced. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electric circuit of a heater control unit in an image forming apparatus to which the present invention is applied.

FIG. 2 is a block diagram showing an electric circuit of the laser beam printer to which the present invention is applied.

FIG. 3 is a diagram illustrating an input voltage waveform, a current waveform of each heater, and a heater current control according to the first embodiment of the present invention.
FIG. 4 is a timing chart showing a relationship between control signals of respective heaters and a current waveform obtained by combining all of the control signals.

FIG. 4 is a timing chart showing a relationship between a heater control signal of the heater current control and a voltage and a current of the heater according to the first embodiment of the present invention in more detail than FIG.

FIG. 5 is a timing chart showing a relationship between heater control signals (A) and (B) according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between heater control signals (A) and (B) according to the second embodiment of the present invention, and is a timing chart when the heater current is less than 50%.

FIG. 7 is a diagram illustrating a relationship between a heater control signal and a voltage and a current of a heater according to the second embodiment of the present invention, and is a timing chart when the current of the heater is less than 50%.

FIG. 8 is a diagram illustrating a relationship between heater control signals (A) and (B) according to the second embodiment of the present invention, and is a timing diagram when a heater current is 50% or more.

FIG. 9 is a diagram illustrating a relationship between a heater control signal and a voltage and a current of the heater according to the second embodiment of the present invention, and is a timing chart when the current of the heater is 50% or more.

FIG. 10 is a diagram illustrating a relationship between heater control signals (A) and (B) according to a third embodiment of the present invention, and is a timing chart when a heater current is less than 50%.

FIG. 11 is a diagram illustrating a relationship between heater control signals (A) and (B) according to a third embodiment of the present invention, and is a timing diagram when a heater current is 50% or more.

FIG. 12 is a diagram showing a relationship between heater control signals (A) and (B) according to a fourth embodiment of the present invention, and is a timing chart when the heater current is less than 50%.

FIG. 13 is a timing chart in a case where t3 occurs before t2 according to the fourth embodiment of the present invention.

FIG. 14 is a diagram illustrating a relationship between heater control signals (A) and (B) according to a fifth embodiment of the present invention, and is a timing chart when a heater current is 50% or more.

FIG. 15 is a side sectional view showing a configuration of a conventionally known image forming apparatus.

FIG. 16 is a block diagram illustrating an electric circuit of a heater and a heater control unit of a conventionally known image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 power switch 2 noise filter 3 fuser control unit 4 low voltage power supply unit 5 temperature sensor 6 fan 7 fan motor driver 8 light receiving element 9 BD circuit 10 high voltage power supply 11 scanner motor 12 scanner motor driver 13 main motor 14 main motor driver 15 paper Size sensor 16 Paper presence sensor 17 Door sensor 18 Feed sensor 19 Discharge sensor 20 Cartridge sensor 21 Video I / F circuit 100 Video controller unit 101 Host I / F circuit 103 Video controller 103a CPU 103b RAM 103c ROM 103d Buffer 103f Non-volatile storage Medium 104 Operation panel 105 Engine controller 105a CPU 105b RAM 105c ROM 106 Laser driver 107 Laser diode 108 a polygon mirror 109 mirror 110 the laser light 111 the primary charger 112 photosensitive drum 113 developing device 114 transfer charger 115 cleaning device 116 fuser 117 fixing roller 118 pressure roller 119 fixing heater 120 paper feed cassette 121 paper feed roller

Claims (11)

[Claims] An image forming apparatus including a heater as a fixing unit for fixing a coloring material on a recording material; a plurality of heating elements used as the heater; a detection unit detecting a temperature of the heating element; An image forming apparatus comprising: a control unit that individually performs PWM driving of a current flowing through each of the heating elements in response to a detection output of the detection unit. 2. An image forming apparatus comprising a plurality of heaters as fixing means for fixing a developing material to a recording medium, wherein a plurality of current control means for controlling a current flowing through the heaters connected in parallel for each heater. An image forming apparatus comprising: 3. The image forming apparatus according to claim 1, wherein the currents supplied to the heaters are controlled so as not to overlap. 4. The image forming apparatus according to claim 1, wherein when the number of the heaters is two, the phase of a signal for controlling each heater is shifted by a half cycle. 5. The image according to claim 1, wherein when the number of heaters is three, the phase of a signal for controlling each heater is controlled by shifting by one-third cycle. Forming equipment. 6. The method according to claim 1, wherein when the number of heaters is two, the ON timing of the control signal in the first heater and the OFF timing of the control signal in the second heater are performed simultaneously. An image forming apparatus comprising: 7. The method according to claim 1, wherein when the number of heaters is two, the start of the ON timing of the control signal in the first heater and the start of the OFF timing of the control signal in the second heater. And controlling the end of the OFF timing of the control signal in the first heater and the end of the OFF timing of the control signal in the second heater to the same timing. Forming equipment. 8. The image forming apparatus according to claim 1, wherein the heaters are controlled such that respective heat values of the heaters are equal. 9. The fixing device according to claim 1, wherein when the temperature of the fixing unit is raised from room temperature to a temperature at which fixing can be performed, currents flowing through the plurality of heaters are controlled so as to overlap each other. An image forming apparatus, wherein when the fixing of the recording material or the recording medium is performed after reaching, the currents of the plurality of heaters are controlled so as not to overlap. 10. A method of fixing a developer on a recording medium using a fixing device having a plurality of heaters, wherein currents flowing through the plurality of heaters are individually PWM-controlled. Image forming method. 11. A program for individually performing PWM control of a current flowing through a heater having a plurality of heaters when a developer is fixed on a recording medium using a fixing device having a plurality of heaters. A storage medium storing an image forming procedure, wherein the image forming procedure is stored in the storage unit.