JP2016024435A - Image forming apparatus and fixation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the variation of a bias voltage and preventing the deterioration in quality of a formed image, such as image unevenness.SOLUTION: In an image forming apparatus, a heater is provided in a fixation roller, and the temperature of the heater is detected by, for example, a thermistor provided in the vicinity of the heater. The image forming apparatus removes from a signal representing a detected temperature of the heater a DC component of the signal to extract an AC component. Then, the image forming apparatus generates an AC voltage having an opposite phase to that of the extracted AC component, and generates a bias voltage on the basis of a voltage obtained by adding the generated AC voltage having the opposite phase to a prescribed target voltage. Further, the image forming apparatus applies a voltage based on the generated bias voltage to charge the fixation roller and other components of the image forming apparatus.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus and a fixing method thereof, and more particularly, to an image forming apparatus such as a copying machine and a printer, and a fixing method thereof.

  2. Description of the Related Art Conventionally, an image forming apparatus according to an electrophotographic system includes a fixing unit that thermally fixes a formed image transferred to a recording medium such as a recording sheet. In the fixing unit, a recording medium on which a toner image is transferred is sandwiched between a fixing roller having a heating resistor (fixing heater) on the inside and a pressure roller in contact with the fixing roller. The toner image is fixed by heating while applying pressure. Further, such a fixing device employs a technique for suppressing the tail offset of the toner in the nip portion by applying a voltage having the same polarity as the toner to the fixing roller. Such a technique is known as an on-demand fixing method.

  In addition, the image forming apparatus according to the electrophotographic system includes a high voltage power supply unit for supplying a high voltage to the fixing unit. A conventional high-voltage power supply unit of an image forming apparatus is one for a device using a plurality of high voltages such as a primary charger, a transfer unit, and a developing unit in order to simplify the circuit configuration and realize cost reduction. High voltage is supplied from two transformers.

JP-A-6-332299

  However, in the above conventional example, there are the following problems when applying a technique for outputting a plurality of high voltages from one transformer to a fixing unit of an image forming apparatus adopting an on-demand fixing method. That is, since the heater and the fixing film are provided in pressure contact, a stray capacitance is formed in relation to the gap length between the heater and the fixing film surface, and the AC voltage of the commercial power supply passes through the fixing portion, the stray capacitance, and the fixing film. It will sneak into the primary charger from the bias. As a result, the AC voltage of the commercial power supply is superimposed on the charging bias, causing image unevenness and the like.

  The present invention has been made in view of the above-described conventional example, and provides an image forming apparatus and a fixing method thereof capable of suppressing high-definition image formation by suppressing fluctuation in charging bias voltage, preventing occurrence of image unevenness, and the like. It is an object.

  In order to achieve the above object, the image forming apparatus of the present invention has the following configuration.

  That is, an image forming unit that forms an image on a recording medium, and an image forming apparatus that thermally fixes an image formed on the recording medium by the image forming unit, which is heated by applying an AC voltage from an AC power source. A first roller provided with a heater and a second roller that rotates in pairs with the first roller, and the recording medium is sandwiched between the first roller and the second roller. A fixing unit for fixing the image by heating and conveying the recording medium while rotating the first roller and the second roller; and a temperature of the heater. Detection means for detecting, filter means for removing a DC component of the signal from the signal representing the temperature of the heater detected by the detection means, and extracting an AC component; and AC component extracted by the filter means A bias voltage based on a first generation unit that generates an AC voltage having an opposite phase to the target voltage, and a voltage obtained by adding the AC voltage having the opposite phase generated by the first generation unit to a predetermined target voltage. A second generation unit for generating the first charging unit and a charging unit that applies a voltage based on the bias voltage generated by the second generation unit to charge the first roller and the other components of the image forming apparatus. Means.

  Another aspect of the present invention is an image forming unit that forms an image on a recording medium, and a fixing method of an image forming apparatus that thermally fixes an image formed on the recording medium by the image forming unit. The image forming apparatus includes a first roller provided with a heater that is heated by applying an AC voltage from an AC power source, and a second roller that rotates in pairs with the first roller. The recording medium is sandwiched between the first roller and the second roller, and the recording medium is heated and conveyed while rotating the first roller and the second roller, and the image is displayed. The fixing method includes: a detecting step for detecting the temperature of the heater by a detecting unit provided in the vicinity of the heater; and a signal representing the temperature of the heater detected in the detecting step. The faith A filter step for removing the direct current component and taking out the alternating current component, a first generation step for generating an alternating current voltage having a phase opposite to that of the alternating current component taken out in the filter step, A second generation step for generating a bias voltage based on a voltage obtained by adding the reverse-phase AC voltage generated in the generation step, and a voltage based on the bias voltage generated in the second generation step. A fixing method comprising: a charging step of applying and charging the first roller and the other components of the image forming apparatus.

  Therefore, according to the present invention, there is an effect that the fluctuation of the bias voltage caused by the AC voltage of the AC power source can be suppressed, and the deterioration of the quality of the formed image such as image unevenness can be prevented.

1 is a side sectional view showing a configuration of a multi-function printer (MFP) apparatus that is a typical embodiment of the present invention. FIG. 2 is a side sectional view showing a schematic configuration of a film heating type fixing device used in the MFP apparatus shown in FIG. 1. FIG. 2 is a diagram illustrating a circuit configuration of a power supply circuit and a fixing device of the MFP apparatus illustrated in FIG. 1. It is a figure which shows the waveform of the output voltage of each part of a power supply circuit and a fixing device.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings.

  In this specification, “recording medium” refers to not only paper used in general recording apparatuses but also a wide range of materials such as cloth, plastic film, metal plate, glass, ceramics, wood, leather, etc. It shall also represent what is possible.

  FIG. 1 is a side sectional view showing a configuration of a multi-function printer apparatus (hereinafter referred to as MFP apparatus) 100 as a typical embodiment of the present invention.

  The MFP apparatus 100 includes a printer unit (image forming apparatus) 101 that forms an image according to an electrophotographic method, a reader unit 102 that reads an image, and an ADF unit 103 that conveys a read document.

  The printer unit 101 includes a cassette 110 that stores the recording medium P, and the recording medium P is fed from the cassette 110 by a pickup roller 111 and a feeding roller 112. The fed recording medium P is separated and fed by the retard roller 113 to be separated one by one, and then the recording medium P is further conveyed by the conveying roller 114. Thereafter, when the skew correction of the recording medium P is performed by the stopped registration roller pair 115, the registration clutch CL1 (not shown) is driven and connected to rotate the registration roller pair 115 to the image forming unit 130. It is conveyed.

  In the image forming unit 130, the outer peripheral surface of the photosensitive drum 131 is uniformly charged to a predetermined polarity potential by the photosensitive drum 131 and the charging roller 132. The laser scanner 120 scans the photosensitive drum 131 with the laser light L modulated according to the time-series digital pixel signal of the image information, so that an electrostatic latent image is formed on the photosensitive drum 131. Thereafter, the electrostatic latent image on the photosensitive drum 131 is developed as a toner image by the developing roller 141 of the developing device 140. A transfer bias having a polarity opposite to that of the photosensitive drum 131 is applied to the transfer roller 133, so that the toner image on the photosensitive drum 131 is electrostatically transferred onto the recording medium P.

  In the fixing device 150, a nip is formed by the heating roller 10 and the pressure roller 20 in which a heater is disposed on the inner side and a fixing film is mounted on the outer periphery. When the recording medium P reaches the nip portion, the toner image on the recording medium P is heated and melted and fixed by the heat and pressure of the heater. Thereafter, the recording medium P is discharged out of the apparatus by the discharge roller 160.

  In double-sided recording, the recording medium P that has passed through the fixing device 150 is stopped and reversed at the discharge unit, switched back, and conveyed to the reverse conveyance path 170. At that time, the conveyance path is switched by its own weight by the reverse flapper 171 so that the recording medium P does not return to the fixing device 150 again. In the reverse conveyance path 170, the recording medium P is conveyed to the registration roller pair 115 by the reverse roller 172, and after performing skew correction again, image formation on the back surface is performed.

  FIG. 2 is a side sectional view showing a more detailed configuration of the film heating type fixing device.

  The fixing device 150 includes the heating roller 10 and the pressure roller 20. The heating roller 10 has a heater 11 fixed to a heat resistant stay holder (support) 12, and a cylindrical thin film (fixing film) 13 of a heat resistant resin is disposed outside the heater 11 to add elasticity. The pressure roller 20 is pressed against the heater 11 via the fixing film 13. As a result, a nip portion having a predetermined width is formed between the fixing film 13 and the pressure roller 20. The pressure roller 20 is provided with an elastic layer 22 inside and a release layer 23 on the outer periphery thereof, and rotates around the rotation shaft 21.

  As shown in FIG. 2, the fixing film 13 covers the outer periphery of the heating roller 10 and is installed so that the heater 11 and a part thereof are in pressure contact. The heater 11 is glass-coated to be insulated from the fixing film 13. A negative high voltage (film bias) from a high voltage power circuit (described later) is applied to the fixing film 13.

  The heater 11 is heated by energization, and the heater temperature is detected by a thermistor 14 installed on the back surface of the heater 11 and fed back to a CPU (described later) of the MFP apparatus 100, whereby the heater 11 is heated to a predetermined fixing temperature. It is adjusting. The heater 11 includes a heating resistor driven by a commercial AC power source (described later), a ceramic substrate having good thermal conductivity, and a glass pattern for insulation.

  In order to fix the toner image on the recording medium P, the heater 11 is adjusted to the fixing temperature, the fixing film 13 is rotated in the direction of the arrow, and in this state, the toner image is applied to the nip portion between the fixing film 13 and the pressure roller 20. The supported recording medium P is introduced through the guide 15. The recording medium P is in close contact with the surface of the fixing film 13, and the nip portion is nipped and conveyed together with the fixing film 13. While the recording medium P passes through the nip portion, the recording medium P and the toner image thereon are heated by the heater 11 via the fixing film 13, and the toner image is thermally fixed to the recording medium P. The recording medium P that has passed through the nip portion is peeled off from the surface of the fixing film 13 and conveyed outside the fixing device 150 through the guide 16. A conveying roller 17 and a driven roller 18 are provided outside the fixing device 150, and the recording medium P is further conveyed by these roller pairs.

  FIG. 3 is a circuit diagram showing configurations of the fixing device, the power supply circuit, and the AC voltage inverting circuit.

  Although the structure of the fixing device 150 has been described with reference to FIG. 2, the fixing device 150 electrically adopts an on-demand fixing method, and the heater 11, the commercial AC power source 203, the fixing film 13, the pressure roller 20, and the thermistor 14. , A thermo switch 153.

  The thermistor 14 is placed in contact with the surface of the heater 11 in order to detect the surface temperature of the heater 11. As a resistance value reading circuit of the thermistor 14, a resistor 151 and a DC power source 152 are provided as shown in FIG. Since the resistance value of the thermistor 14 changes depending on the temperature of the heater 11, the voltage applied to the thermistor 14 changes as the detection temperature of the thermistor 14 changes. The voltage from the thermistor 14 is input to the CPU 201, and the CPU 201 can read the temperature of the heater 11.

  The thermo switch 153 is installed in contact with the heater 11 separately from the thermistor 14 in order to ensure the safety of the heater 11 and prevent ignition due to overheating. When the temperature of the heater 11 is detected and detected above a specific temperature, the heater 11 is forcibly turned off. In this embodiment, a thermo switch that does not return once turned off is selected.

  As can be seen from FIG. 3, since the heater 11 and the fixing film 13 are in contact with each other, the stray capacitance C <b> 1 exists in proportion to the gap D <b> 1 between the heater 11 and the surface of the fixing film 13. Therefore, when the AC voltage Vac is applied from the commercial AC power supply 203 to the heater 11 for fixing the toner image, the AC voltage Vac is applied to the charging bias Vbias to the charging roller 132 through the stray capacitance C1 through the following path. Superimposed. That is, as indicated by the thick arrow in FIG. 3, the AC voltage Vac is superimposed on the bias voltage Vbias through the path of the commercial AC power source 203 → heater 11 → floating capacitance C1 → signal line 154 → resistance 207 → resistance 206 → charging roller 132. . As a result, the charging bias Vbias varies. This causes the fixing operation of the fixing device 150 to become unstable, and as a result, image unevenness occurs.

  The power supply circuit 200 includes a CPU 201 that controls the entire MFP apparatus 100, a transformer 204, a transformer drive circuit 214, an operational amplifier (OP) 211 that causes the output voltage of the transformer to follow the target voltage, an AC inversion voltage application circuit 401, and the like. including. The transformer 204 boosts DC 24V to several tens of times according to the winding ratio, and the transformer drive circuit 214 oscillates to drive the transformer 204 because the transformer 204 does not operate with DC. In addition, the power supply circuit 200 includes an emitter follower circuit, a resistor that divides the output voltage of the transformer 204, and the like.

  The output voltage from the power supply circuit 200 is determined by the winding ratio of the transformer 204, the resistance values of the resistors 205, 206, and 207 and the target voltage. The output voltage is output as a charging bias Vbias for the charging roller 132 and is also output via a signal line 154 as a film bias for the fixing film 13.

  The PWM signal output from the CPU 201 is smoothed to a direct current by the smoothing circuit 209 and output as the target voltage Vtarget. The CPU 201 changes the duty ratio of the PWM signal. The value of the DC voltage output from the smoothing circuit 209 changes, that is, the magnitude of the target voltage Vtarget is changed.

  In this embodiment, the relationship between the charging bias Vbias and the thermistor 14 is focused on the fact that the AC voltage value is a proportional relationship and the phase is an in-phase relationship, and the AC voltage of the thermistor 14 is detected to be superimposed on the charging bias Vbias. Predict the AC voltage component. Then, based on the detection result of the AC voltage in the thermistor 14, an AC voltage IVac having an opposite phase to the AC voltage component of the charging bias Vbias is generated by the AC inversion voltage generation circuit 301, and the AC voltage IVac having the opposite phase is fed back. That is, as shown in FIG. 3, an AC voltage IVac having an opposite phase is applied to the primary side of the AC inversion voltage generation circuit 301 → the AC inversion voltage application circuit 401 → the operational amplifier 211 → the transistor 212 → the transformer 204. In this way, the voltage fluctuation of the charging bias Vbias is suppressed.

  Next, the voltage relationship between the charging bias Vbias and the thermistor 14 will be described with reference to the voltage waveform diagram shown in FIG.

  First, FIG. 4I shows the AC voltage Vac from the commercial AC power source 203.

  Similar to the space between the heater 11 and the fixing film 13, a stray capacitance C <b> 2 exists in proportion to the gap length D <b> 2 between the heater 11 and the thermistor 14. The AC voltage Vac is superimposed on the thermistor 14 from the commercial AC power supply 203 through the stray capacitance C <b> 2 through the path of the heater 11 → the stray capacitance C <b> 2 → the thermistor 14. Therefore, a voltage proportional to the magnitude of the voltage applied to the heater 11 is superimposed on the thermistor 14. This also appears in the time change of the thermistor voltage Vtm shown in (iii) of FIG.

  On the other hand, since the relationship between the charging bias Vbias and the voltage of the heater 11 is proportional and the relationship between the voltage of the heater 11 and the thermistor 14 is proportional, the AC component of the charging bias Vbias and the thermistor voltage Vtm is proportional. .

  It can be said that the heater 11, the bias voltage Vbias, and the thermistor 14 are connected by a single capacitor called stray capacitance. Therefore, as shown in FIGS. 4 (ii) and 4 (iii), the bias voltage Vbias and the phase of the AC component of the thermistor voltage are in phase. Therefore, as described above, the magnitudes of the AC components of the bias voltage Vbias and the thermistor voltage Vtm are proportional and the phases are in phase.

  Focusing on this point, in this embodiment, the thermistor voltage Vtm is detected to predict the bias voltage Vbias, and based on the prediction, the AC inversion voltage generation circuit 301 generates a voltage having an opposite phase. Then, the voltage IVac having the opposite phase is fed back to the primary side of the transformer 204 and applied. In this way, the inverted voltage of the AC voltage superimposed on the bias voltage Vbias is further superimposed on the bias voltage Vbias. As a result, as shown in FIG. 4 (vii), the fluctuation of the bias voltage Vbias due to the AC voltage can be suppressed.

  Next, the above operation will be described according to the circuit configuration shown in FIG.

  The AC inversion voltage generation circuit 301 removes the DC component from the voltage Vtm detected from the thermistor 14, extracts only the AC component, generates an AC voltage IVac that is inverted, and feeds it back to the power supply circuit 200. Then, the inverted AC voltage IVac is applied to the primary side of the transformer 204.

The AC inversion voltage generation circuit 301 includes a high pass filter (HPF) 302 including a capacitor 304 and a resistor 305, and an inverting amplification circuit 303. As shown in FIGS. 4 (iii) and 4 (iv), the high pass filter (HPF) 302 removes the DC voltage component of the thermistor voltage Vtm and extracts only the AC voltage component V _HPF .

The inverting amplifier circuit 303 includes a resistor 306, a variable resistor 307, and an operational amplifier 308. The output voltage from the inverting amplifier circuit 303 is determined from the sizes of the resistor 306 and the variable resistor 307. The inverting amplifier circuit 303 generates a voltage IVac having a phase opposite to that of the output voltage V _HPF from the high pass filter (HPF) 302 as shown in FIG.

  The inverted voltage IVac is determined by changing the variable resistor 307 of the inverting amplifier circuit 303 so as to suppress the voltage fluctuation of the bias voltage Vbias to zero.

  That is, the voltage amplification factor in the inverting amplifier circuit 303 is determined as follows.

  As described above, the AC component of the bias voltage Vbias and the thermistor voltage Vtm is in a proportional relationship. Therefore, for example, the magnitude of the AC component of the bias voltage Vbias and the thermistor voltage Vtm is measured at the time of shipment from the factory, and the variable resistor 307 is adjusted so as to suppress the AC component variation of the bias voltage Vbias to zero based on the result. In this way, the voltage amplification factor of the inverting amplifier circuit 303 is determined.

  Finally, the AC inversion voltage application circuit 401 included in the power supply circuit 200 will be described.

  The AC inversion voltage application circuit 401 includes an operational amplifier (OP) 404, a resistor 405, a resistor 406, and a resistor 407, and is a circuit that can perform an addition operation. In the AC inversion voltage application circuit 401 shown in FIG. 3, if the resistance values of the resistors 405 to 407 are the same, the sum of the inversion voltage IVac that is the output of the AC inversion voltage generation circuit 301 and the target voltage Vtarget is added to the output of the operational amplifier 404. Voltage is output. The voltage (IVac + Vtarget) generated in this way is output to the operational amplifier (OP) 211.

  The operational amplifier (OP) 211 has a configuration of a differential amplifier in which the output voltage is controlled by the difference between the sum of the generated voltage (IVac + Vtarget) and the feedback voltage and the DC voltage from the DC power supply 215. The output from the operational amplifier (OP) 211 is input to the gate of the transistor 212, and when the voltage exceeds the threshold voltage, the voltage from the DC power supply 213 is applied to the primary side of the transformer 204. This applied voltage Vprim is shown in FIG.

  As can be seen by comparing FIG. 4 (v) and FIG. 4 (vi), the AC component of the applied voltage Vprim on the primary side of the transformer 204 has the same phase as the inverted voltage IVac that is the output of the AC inverted voltage generation circuit 301. Voltage.

  A voltage reflecting the phase is generated on the secondary side of the transformer 204. Here, as described above, an AC component reflecting the phase of the AC voltage Vac appears from the commercial AC power supply 203 via the signal line 154 and is superimposed on the bias voltage Vbias. On the other hand, on the secondary side of the transformer 204, a voltage having a phase opposite to that of the phase is generated, and these voltages are combined at the connection point 216. As a result, a bias voltage Vbias in which the AC component is canceled is generated. It will be. The result is as shown in FIG. 4 (vii).

  Therefore, according to the embodiment described above, the AC voltage component superimposed on the thermistor is detected, and the AC voltage component superimposed on the charging bias is predicted. On the other hand, based on the detection result of the thermistor voltage, an AC voltage having a phase opposite to the AC component of the charging bias is generated and applied to the primary side of the transformer. By doing so, the charging bias is synthesized with a voltage including an AC component having a phase opposite to that of the AC component of the commercial AC power source transmitted via a signal provided for applying a negative voltage to the fixing film. Will be generated.

  As a result, since the AC component is canceled from the generated bias voltage, it is possible to suppress the voltage fluctuation of the bias voltage, and it is possible to uniformly charge the fixing device, and good image formation and fixing. Can be realized.

  In this embodiment, a thermistor is provided in the vicinity of the heater of the fixing device to detect the AC voltage, but the present invention is not limited to this. Thermistor may be used as long as it is installed near the heater of the fixing device and can detect an AC voltage (electrically conductive). For example, a temperature fuse, a thermo switch, a fixing heater conductive portion It may be.

  In this embodiment, the output from the transformer is described as being for the charging roller and the fixing film, but the present invention is not limited to this. The output of the bias voltage with respect to another component, for example, a developing device bias voltage and a fixing film, may be sufficient.

Furthermore, in the above-described embodiments, the MFP apparatus has been described as an example. However, the present invention is not limited to this, and for example, the present invention can be applied to a single-function printer apparatus.

10 heating roller, 11 heater, 13 fixing film, 14 thermistor,
20 pressure roller, 100 multifunction printer device (MFP device),
101 printer unit (image forming apparatus), 102 reader unit,
103 ADF unit, 132 charging roller, 150 fixing device, 201 CPU,
203 AC power supply, 204 transformer 214 transformer drive circuit 301 AC inversion voltage generation circuit, 401 AC inversion voltage application circuit

Claims (10)

An image forming unit that forms an image on a recording medium, and an image forming apparatus that thermally fixes an image formed on the recording medium by the image forming unit,
A first roller provided with a heater that is heated by applying an AC voltage from an AC power source, and a second roller that rotates in pairs with the first roller, the first roller and the A fixing unit that fixes the image by sandwiching the recording medium with a second roller and heating and conveying the recording medium while rotating the first roller and the second roller;
A detecting means provided in the vicinity of the heater for detecting the temperature of the heater;
Filter means for removing a direct current component of the signal from a signal representing the temperature of the heater detected by the detection means and extracting an alternating current component;
First generating means for generating an AC voltage having a phase opposite to that of the AC component extracted by the filter means;
Second generation means for generating a bias voltage based on a voltage obtained by adding the reverse-phase AC voltage generated by the first generation means to a predetermined target voltage;
An image comprising: a charging unit that applies a voltage based on the bias voltage generated by the second generation unit to charge the first roller and other components of the image forming apparatus. Forming equipment. The outer periphery of the first roller is covered with a fixing film,
The image forming apparatus according to claim 1, wherein the fixing film is charged by the charging unit.   The image forming apparatus according to claim 2, wherein the AC voltage is superimposed on the bias voltage through a first stray capacitance formed between the fixing film and the heater. The detection means includes a thermistor,
The AC voltage is detected by the thermistor through a second stray capacitance formed between the heater and the thermistor and is superimposed on a signal representing the temperature of the heater,
The image forming apparatus according to claim 3, wherein the alternating voltage superimposed on the bias voltage and the alternating voltage superimposed on a signal representing the temperature of the heater have the same phase. The first generation unit includes an inverting amplifier circuit that generates an AC voltage having a phase opposite to that of the AC component extracted by the filter unit;
The amplification factor of the inverting amplifier circuit is obtained by measuring the AC component of the bias voltage and the AC component of the output voltage from the thermistor in advance, and based on the measurement result, the fluctuation due to the AC component of the bias voltage is reduced. The image forming apparatus according to claim 4, wherein the image forming apparatus is determined to be zero.   The image forming apparatus according to claim 1, wherein the filter unit includes a high-pass filter that removes the DC component. The second generation means includes
Adding means for adding the target voltage and the AC voltage of the opposite phase;
7. The transformer according to claim 1, further comprising: a transformer on the primary side that is applied with a voltage based on the output voltage from the adding means and that outputs the bias voltage from the secondary side. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the another component includes a developing unit included in the image forming unit or a charging roller that charges the developing unit. .   The image forming apparatus according to claim 1, wherein the image forming unit forms a toner image on the recording medium based on an electrophotographic method. An image forming unit that forms an image on a recording medium, and a fixing method of an image forming apparatus that thermally fixes an image formed on the recording medium by the image forming unit,
The image forming apparatus includes a first roller provided with a heater that is heated by applying an AC voltage from an AC power source, and a second roller that rotates in pairs with the first roller, The recording medium is sandwiched between the first roller and the second roller, and the recording medium is heated and conveyed while rotating the first roller and the second roller, thereby fixing the image. Fixing means for performing the fixing,
A detection step of detecting the temperature of the heater by a detection means provided in the vicinity of the heater;
A filter step for removing a direct current component of the signal from a signal representing the temperature of the heater detected in the detection step and extracting an alternating current component;
A first generation step of generating an AC voltage having a phase opposite to that of the AC component extracted in the filtering step;
A second generation step of generating a bias voltage based on a voltage obtained by adding the reverse-phase AC voltage generated in the first generation step to a predetermined target voltage;
And a charging step of charging the first roller and other components of the image forming apparatus by applying a voltage based on the bias voltage generated in the second generation step. Method.

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