Image forming apparatus

Abstract

To achieve efficient heating while reducing flicker according to a voltage value of an AC voltage.SOLUTION: An image forming apparatus has heating elements that generate heat with power supplied from an AC power supply, and fixes a toner image to a sheet by using the heat. Switches are provided between the AC power supply and the heating elements. After starting supply of power from the AC power supply to the heating elements, the image forming apparatus makes a rush current difficult to flow from the AC power supply to the heating elements over a predetermined time. The image forming apparatus determines, on the basis of, voltage information on the AC power supply, at least one of a length of the predetermined time and the on-time of the switches per half period of an alternating current from the AC power supply applied to the switches in the predetermined time.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an image forming apparatus having a fixing device for fixing a toner image on a sheet.

Background Art

[0002] The fixing device applies heat to the toner image and the sheet using a plurality of heaters to fix the toner image on the sheet. Patent Document 1 discloses a fixing device employing a halogen heater. Since an inrush current flows through the halogen heater when it is started up, the power supply voltage of the AC power supply drops, and a so-called flicker phenomenon may occur. The flicker phenomenon refers to a phenomenon in which the voltage of the AC power supply fluctuates due to an inrush current or the like generated in an electrical device connected to the AC power supply, and the operation of other devices connected to the AC power supply is affected. A typical flicker phenomenon is the flickering of a lighting device. According to Patent Document 2, it has been proposed to reduce flicker by gradually increasing the conduction angle (conduction time for each half cycle of the alternating current) of the alternating voltage applied to the halogen heater during the start-up period of the halogen heater.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the voltage (rated voltage) of a commercial AC power supply may vary from country to country or from region to region within the same country. Furthermore, there may be a plurality of commercial AC power supplies with different voltages provided within the same region. Some commercial power supplies can stably provide an AC voltage with little fluctuation with respect to the rated voltage, while others provide an AC voltage with large fluctuations with respect to the rated voltage. For example, there are regions where the effective value of the AC voltage supplied from a commercial power supply fluctuates greatly between +10% and -10%. Furthermore, there are also regions where the effective value actually fluctuates in the range of 180V to 270V with respect to a rated voltage of 220V. Under such power supply conditions, if the conduction angle or the length of the startup period is fixed according to the AC voltage with a high effective value during the startup period, the heating time of the heater will become long when an AC voltage with a low effective value is applied. Conversely, if the conduction angle or the length of the startup period is fixed according to the AC voltage with a low effective value during the startup period, the flicker reduction effect will be insufficient when an AC voltage with a high effective value is applied. Therefore, an object of the present invention is to reduce flicker according to the voltage value of an AC voltage and to achieve efficient heating.

Means for Solving the Problem

[0005] The present invention is, for example, image forming means for forming an image on a sheet, fixing means for fixing the image on the sheet, A first heating element that generates heat by the power supplied from a first AC power source, and a second heating element that generates heat by the power supplied from a second AC power source different from the first AC power source having the fixing means, The value of a first AC voltage supplied from the first AC power source and the value of a second AC voltage supplied from the second AC power source voltage detection means for detecting, temperature detection means for detecting the temperature of the fixing means, energization means for energizing the fixing means, control means for controlling the energization means based on the detection result of the temperature detection means, and an image forming apparatus having the same, After the power is Turn on supplied to the image forming apparatus 、 the First heating element and the second heating element During the startup operation of starting the supply of power to raise the temperature of the fixing means to a predetermined target temperature, (i) From the start of supplying power to the heating element until First a predetermined period elapses, limit the duty ratio of energizing the heating element to a First predetermined duty ratio determined in advance and supply power in a reduced control mode; First and First (ii) after the predetermined period has elapsed since the start of supplying power to the heating element, cancel the limitation of the duty ratio of energizing the heating element to the predetermined duty ratio, and control the duty ratio of energizing the heating element based on the temperature of the fixing means in a temperature control mode, and the control means can execute the above, and after the power is supplied to the image forming apparatus, before executing the reduced control mode, detect the AC voltage supplied from the AC power source by the voltage detecting means, and provide an image forming apparatus characterized in that it is configured as described above. and until a second predetermined period has elapsed after starting to supply power to the second heating element, limit the duty ratio for energizing the second heating element to a predetermined second duty ratio (ii) First After the start of supplying power to the heating element and after the First predetermined period has elapsed, cancel the limitation of the duty ratio of energizing the heating element to the First predetermined duty ratio, and based on the temperature of the fixing means, First control the duty ratio of energizing the heating element, and can execute a temperature control mode, and after the second predetermined period has elapsed after starting to supply power to the second heating element, release the limitation of the duty ratio for energizing the second heating element to the second predetermined duty ratio and First the heating element and the second heating element is energized, and the control means, after the power is supplied to the image forming apparatus, before executing the reduced control mode, Turn on detects the First AC voltage The first supplied from the AC power source value and the value of the second AC voltage supplied from the second AC power source by the voltage detecting means, Determine the first predetermined duty ratio of the first heating element when the first heating element is first turned on after the image forming apparatus is powered on, based on the value of the first AC voltage, and determine the second predetermined duty ratio of the second heating element when the second heating element is first turned on after the image forming apparatus is powered on, based on the value of the second AC voltage and is configured as described above. An image forming apparatus characterized by the above is provided.

Advantages of the Invention

[0006] According to the present invention, it is possible to reduce flicker according to the voltage value of the AC voltage and realize efficient heating.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0009] <Example 1> [Image forming apparatus] As shown in FIG. 1, the image forming apparatus 100 is an electrophotographic printer having four image forming stations. The image forming apparatus 100 may be commercialized as a copier, a multifunction machine, a facsimile apparatus, or the like. Here, the first station forms a yellow (y) image. The second station forms a magenta (m) image. The third station forms a cyan (c) image. The fourth station forms a black (k) image. The operations and configurations of the four stations are the same or similar. Therefore, when matters common to the four colors are described, the characters ymck are omitted from the reference numerals. Note that the technical idea of the present invention is also applicable to a monochrome printer.

[0010] The photosensitive drum 101 is a photoreceptor and an image carrier that rotates while carrying an electrostatic latent image and a toner image. The charging roller 102 is a charging member that uniformly charges the surface of the photosensitive drum 101. The exposure device 103 irradiates the photosensitive drum 101 with laser light E according to an image signal to form an electrostatic latent image on the surface of the photosensitive drum 101. The developing device 104 forms a toner image by attaching toner to the electrostatic latent image. The primary transfer roller 105 transfers the toner image from the photosensitive drum 101 to the intermediate transfer belt 107. That is, a full-color image is formed by sequentially transferring a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image to the intermediate transfer belt 107. As the intermediate transfer belt 107 rotates, the toner image is conveyed to the secondary transfer section. A pair of secondary transfer rollers 109 is provided in the secondary transfer section.

[0011] The paper feed cassette 111 is a paper feed bin capable of accommodating a large number of sheets P. The pickup roller 112 feeds the sheet P from the paper feed cassette 111 to the conveyance path. The paper feed roller 113 conveys the sheet P further downstream while suppressing double feeding of the sheet P. Downstream means downstream in the conveyance direction of the sheet P. The registration roller 114 is a conveyance roller that suppresses skewing of the sheet P. When the leading edge of the sheet P in the conveyance direction of the sheet P abuts against the registration roller 114, the skewing of the sheet P is corrected. Thereafter, the sheet P is conveyed to the secondary transfer section.

[0012] In the secondary transfer section, the pair of secondary transfer rollers 109 transfers the toner image from the intermediate transfer belt 107 to the sheet P. The fixing device 120 fixes the toner image on the sheet P by applying heat and pressure to the sheet P and the toner image. The conveyance rollers 115, 116, and 117 are arranged downstream of the fixing device 120 and convey the sheet P to the discharge roller 118. The discharge roller 118 discharges the sheet P to the outside of the image forming apparatus 100 (e.g., a sheet tray).

[0013] The control board 130 supplies the alternating current supplied from the first commercial power supply 151 and the alternating current supplied from the second commercial power supply 152 to the fixing device 120 and controls the temperature of the fixing device 120. A temperature sensor 131 that detects the temperature of the central region in the extending direction of the fixing device 120 (the direction from the front to the back of the paper surface in FIG. 1) and a temperature sensor 132 that detects the temperature of the end region are provided. In this way, by receiving power from a plurality of different commercial power supplies, it becomes possible to raise the temperature of the fixing device 120 to the target temperature in a short time. Further, compared with the case of using one power supply system, in the case of using a plurality of power supply systems, the inrush current is dispersed, so that flicker is reduced.

[0014] [Fixing device] As shown in FIG. 2, the fixing device 120 has a heating unit 200 centered on an endless and rotatable fixing belt 210 as a heat transfer medium. In FIG. 2, the Z direction is the height direction, and the X direction is a direction parallel to the conveyance direction of the sheet P. The fixing belt 210 is stretched over a pad 220, a heating roller 240, and a tension roller 250. The heating roller 240 is a heating rotating body having a heater (e.g., a halogen heater) inside thereof. A halogen heater is a heater having a halogen lamp as a heating element. The heating roller 240 heats the fixing belt 210. The heating roller 240 rotates by a rotational force supplied from a motor or the like. The tension roller 250 is a tension roller that applies a predetermined tension to the fixing belt 210. The tension roller 250 is biased by an elastic body (e.g., a spring) supported by a frame body (not shown) of the heating unit 200. The tension of this spring is, for example, 50 N. The tension roller 250 rotates passively with respect to the fixing belt 210. The pad 220 supports the inner peripheral surface of the fixing belt 210 by a metal stay 260. The pad 220 cooperates with the pressure roller 230 to sandwich the fixing belt 210. A so-called substantially planar nip portion N is formed between the pad 220 and the pressure roller 230. At least one of the pressure roller 230 or the pad 220 may be biased by a biasing mechanism (not shown) so that the nip portion N having a predetermined length and width is formed. When the sheet P onto which the toner image has been transferred passes through the nip portion N, pressure and heat are applied to the sheet P and the toner image. As a result, the toner image is fixed onto the sheet P.

[0015] The fixing belt 210 has thermal conductivity and heat resistance. The fixing belt 210 has a thin cylindrical shape, and its inner diameter is, for example, 120 mm. The fixing belt 210 may adopt a three-layer structure having a base layer, an elastic layer provided on the outer periphery of the base layer, and a release layer provided on the outer periphery of the elastic layer. The thickness of the base layer is, for example, 60 μm. The material of the base layer is, for example, polyimide resin (PI). The thickness of the elastic layer is, for example, 300 μm. The material of the base layer is, for example, silicone rubber. The thickness of the release layer is, for example, 30 μm. The material of the release layer is, for example, a fluororesin. As the fluororesin, for example, PFA (tetrafluoroethylene·perfluoroalkoxyethylene copolymer resin) etc. can be adopted.

[0016] The material of the pad 220 is, for example, LCP (liquid crystal polymer) resin. The heating roller 240 may be a stainless steel pipe. The outer diameter of the pipe may be, for example, 40 mm. The thickness of the pipe may be, for example, 1 mm. A plurality (e.g., six) of heaters may be disposed inside the pipe. The heat supplied from the heater propagates from the heating roller 240 to the fixing belt 210, and further propagates from the fixing belt 210 to the sheet P and the toner image. The tension roller 250 may also be formed of a stainless steel pipe. The outer diameter of the pipe is, for example, 40 mm. The thickness of the pipe is, for example, 1 mm. The end of the pipe may be rotatably supported by a bearing (not shown).

[0017] The pressure roller 230 is, for example, a roller having an elastic layer and a release layer. An elastic layer is provided on the outer periphery of the rotation axis of the pressure roller 230. Further, a release layer is provided on the outer periphery of the elastic layer. The material of the rotation axis may be metal (e.g., stainless steel). The thickness of the elastic layer is, for example, 5 mm. The material of the elastic layer is, for example, conductive silicone rubber. The thickness of the release layer is, for example, 50 μm. The material of the release layer is, for example, a fluororesin such as PFA.

[0018] [Controller] As shown in FIG. 3, the control board 130 is a controller that drives the heaters 341 to 346. The power cord 351 is connected to the first commercial power supply 151. The power cord 352 is connected to the second commercial power supply 152. The AC power supplied from the power cord 351 is supplied to the first heater group 361 via the first power supply system 311. The AC power supplied from the power cord 352 is supplied to the second heater group 362 via the second power supply system 312. The first heater group 361 includes heaters 341, 342, and 343. The second heater group 362 includes heaters 344, 345, and 346.

[0019] The control board 130 is equipped with a CPU 350 and a plurality of switches 321 to 326. The CPU 350 controls the plurality of switches 321 to 326 according to a control program stored in the memory 360. The memory 360 may include a non-volatile memory (ROM), a volatile memory (RAM), a solid state drive (SSD), a hard disk drive (HDD), and the like.

[0020] Switch 321 is connected between the power cord 351 and the heater 341, and switches the heater 341 on / off according to the control signal 331 from the CPU 350. Switch 322 is connected between the power cord 351 and the heater 342, and switches the heater 342 on / off according to the control signal 332 from the CPU 350. Switch 323 is connected between the power cord 351 and the heater 343, and switches the heater 343 on / off according to the control signal 333 from the CPU 350. Switch 324 is connected between the power cord 352 and the heater 344, and switches the heater 344 on / off according to the control signal 334 from the CPU 350. Switch 325 is connected between the power cord 352 and the heater 345, and switches the heater 345 on / off according to the control signal 335 from the CPU 350. Switch 326 is connected between the power cord 352 and the heater 346, and switches the heater 346 on / off according to the control signal 336 from the CPU 350. The switches 321 to 326 may be switching elements such as, for example, triacs, thyristors, transistors, and IGBTs (insulated gate bipolar transistors). However, the switches 321 to 326 can be controlled by the CPU 350 and can be adopted as long as they are switch elements having performance (rated voltage, rated current) commensurate with the power consumption of the heaters 341 to 346.

[0021] The CPU 350 detects the central temperature M of the heating roller 240 based on the detection signal output from the temperature sensor 131. The CPU 350 detects the end temperature R of the heating roller 240 based on the detection signal output from the temperature sensor 132. The CPU 350 determines the lighting ratio (duty ratio) of each of the heaters 341 to 346 based on these temperatures. The CPU 350 outputs control signals 331 to 336 according to the duty ratio of each of the heaters 341 to 346. The determination of the duty ratio may be performed, for example, at regular intervals (e.g., every 10 seconds).

[0022] The voltage detection circuit 301 detects the voltage of the first commercial power supply 151 and outputs the detection result to the CPU 350. The voltage detection circuit 302 detects the voltage of the second commercial power supply 152 and outputs the detection result to the CPU 350. The voltage detection circuits 301 and 302 may be implemented by a voltage division circuit that outputs a detection voltage proportional to the AC voltage by dividing the AC voltage. Based on the detection result of the first commercial power supply 151, the CPU 350 determines the duty during the startup period of the first heater group 361. Here, the duty refers to the energization time (energization angle) in a half cycle of the AC. The energization angle refers to the angle from the energization start phase to the energization end phase in a half cycle of the AC. Note that the duty ratio is the ratio of the energization time to the half cycle and may be expressed as the ratio of the energization time to the half cycle. Since the startup period is a period during which control for reducing the inrush current and thus flicker is executed, it may also be referred to as the inrush current or flicker reduction control period. The voltage detection circuits 301 and 302 may detect the zero cross of the AC voltage, generate a zero cross signal, and output it to the CPU 350. The zero cross means that the sign (positive or negative) of the AC voltage changes.

[0023] The operation unit 390 includes a display device that outputs information to the user and an input device that receives input from the user. The CPU 350 may obtain information indicating the nominal voltage (or effective value) of the first commercial power supply 151 and information indicating the nominal voltage (or effective value) of the second commercial power supply 152 from the user via the operation unit 390. Note that the effective value may deviate from the nominal voltage. This deviation may occur either long-term or short-term depending on the power supply conditions in each country and region. Therefore, the duty of the first heater group 361 and the duty of the second heater group 362 are determined according to the effective value (or maximum value) detected by the voltage detection circuits 301 and 302. Thereby, more accurate reduction control is realized.

[0024] [Light distribution of the heater (heat generation ability)] FIG. 4(A) shows the light distribution (heat generation capacity distribution) of the three heaters 341, 342, and 343 that form the first heater group 361. FIG. 4(B) shows the light distribution of the three heaters 344, 345, and 346 that form the second heater group 362. The horizontal axis indicates the position in the Y direction. The vertical axis indicates the heat generation capacity. As shown in FIGS. 4(A) and 4(B), the six heaters 341 to 346 may each have a different light distribution. The CPU 350 selects one or more heaters from the six heaters 341 to 346, for example, according to the size and basis weight of the sheet P.

[0025] Y0 indicates the position of one end (hereinafter referred to as the left end) of the heaters 341 to 346. Y3 indicates the position of the other end (hereinafter referred to as the right end) of the heaters 341 to 346. Y1 is the boundary between the end region on the left end side and the central region. Y2 is the boundary between the end region on the right end side and the central region. The length from Y0 to Y3 is, for example, 500 mm. The distance from Y0 to Y1 is, for example, 125 mm. The distance from Y0 to Y2 is, for example, 375 mm. That is, the distance from Y1 to Y2 is 250 mm. Thus, the ratio of the length of one end region to the length of the central region may be 1:2.

[0026] The heaters 341 and 346 are heat sources that mainly heat the central region of the heating roller 240. The heaters 343, 344, and 345 are heat sources that mainly heat the two end regions of the heating roller 240. The heater 342 is a heat source that heats the whole including the central region and the end region of the heating roller 240 almost uniformly.

[0027] The power consumption (heater output) of each of the heaters 341, 342, 345, and 346 is, for example, 1000 W. The power consumption of each of the heaters 343 and 344 is, for example, 500 W. Incidentally, regardless of the width of the sheet P, the center of the sheet P is conveyed so as to pass near the center in the Y direction. For example, when a sheet P with a narrow length (width) in the Y direction is continuously conveyed, the duty of the heaters 343, 344, and 345 that mainly heat the end regions is reduced. Thereby, excessive heat accumulation in both end regions of the heating roller 240 is suppressed.

[0028] As shown in FIGS. 4(A) and 4(B), the temperature sensor 131 is disposed at the center of the central region. The temperature sensor 132 is disposed at the center of the left end region. In particular, by arranging the temperature sensors 131 and 132 so as not to overlap Y1 and Y2, the temperature of the central region (central temperature M) and the temperature of the end region (end temperature R) are accurately detected.

[0029] The ratio of the heat generation capacity of the central region of the heater 341 is X%. The ratio of the heat generation capacity of the end region of the heater 341 is Y% (X > Y). Here, it is assumed that the power consumption of the heater 341 is 1000 W. Therefore, the heat generation capacity of one end region of the heater 341 is 100 W in terms of power. The heat generation capacity of the central region of the heater 341 is 800 W in terms of power. For the remaining heaters 342 to 346, the heat generation capacity of each region can be calculated from the ratios and power consumption shown in FIG. 4(A) or FIG. 4(B).

[0030] [Reduction of Flicker] FIG. 5(A) shows the changes in control signals 331 to 336. FIG. 5(B) shows the changes in the input current I1 input from the first commercial power supply 151 and the changes in the input current I2 input from the second commercial power supply 152. FIG. 5(C) shows the changes in the input voltage V1 input from the first commercial power supply 151 and the changes in the input voltage V2 input from the second commercial power supply 152. Here, it shows that the maximum value of the input voltage V1 is larger than the maximum value of the input voltage V2. That is, it shows that the nominal voltage (rms value) of the first commercial power supply 151 is higher than the nominal voltage (rms value) of the second commercial power supply 152. FIG. 5(D) shows the zero-crossing signals for the first commercial power supply 151 and the second commercial power supply 152. Here, for the sake of simplicity of explanation, only one zero-crossing signal is shown for the first commercial power supply 151 and the second commercial power supply 152. However, the zero-crossing signal of the first commercial power supply 151 and the zero-crossing signal of the second commercial power supply 152 may be different. The period from time t0 to time t3 corresponds to a half cycle of the alternating current.

[0031] Time t0 is the timing at which the CPU 350 starts the temperature control of the fixing device 120. The period from time t0 to time t4 is the inrush current and flicker reduction control period. As the heaters 341 to 346, for example, a heating element whose resistance value changes according to the temperature, such as a halogen heater, may be adopted. In this case, if the temperature of the heaters 341 to 346 is low, the resistance value of the heaters 341 to 346 is also low, so an inrush current easily flows through the heaters 341 to 346. Further, the higher the input voltage, the greater the inrush current. Therefore, the CPU 350 determines the duty for the first heater group 361 during the reduction control period based on the detection result (detection signal 381) of the input voltage V1. Similarly, the CPU 350 determines the duty for the second heater group 362 during the reduction control period based on the detection result (detection signal 382) of the input voltage V2.

[0032] According to FIG. 5(C), the input voltage V1 is higher than the input voltage V2. Therefore, as shown in FIG. 5(A), the duty of the first heater group 361 (the time from time t2 to time t3) is smaller than the duty of the second heater group 362 (the time from time t1 to time t3). In this way, the CPU 350 determines the duty (the energization time or the conduction angle per half cycle) during the reduction control period according to the nominal voltage (effective value) of the AC power supply. Thereby, it is possible to reduce flicker according to the effective value of the AC voltage and realize efficient heating. That is, the heating time required to raise the temperature of the fixing device 120 to the target temperature is shortened.

[0033] Here, the details of the reduction control will be described. Here, it is assumed that the detection results of the input voltages V1 and V2 are determined at a timing before time t0. That is, the CPU 350 determines the duty of the first heater group 361 and the duty of the second heater group 362 and stores them in the memory 360.

[0034] At time t0, the CPU 350 detects the rising edge of the zero-crossing signal. The CPU 350 acquires the duty of the first heater group 361 and the duty of the second heater group 362 from the memory 360 and determines times t1 and t2. During the period from time t1 to time t3, the CPU 350 supplies power to the second heater group 362. During the period from time t2 to time t3, the CPU 350 supplies power to the first heater group 361. In this way, the period from the rising edge of the preceding zero-crossing signal to the rising edge of the succeeding zero-crossing signal is one control cycle. The energization start timing during one control cycle is controlled by the CPU 350. Here, the rising edge of the succeeding zero-crossing signal is the energization end timing. As shown in FIG. 5(A), a plurality of control cycles are repeated during the reduction control period.

[0035] The duty is constant in each control cycle. However, as shown in FIG. 5(B), the inrush current gradually decreases. This is because as the temperatures of the heaters 341 to 346 gradually increase, the resistance values of the heaters 341 to 346 also gradually increase.

[0036] The control mode of the heaters 341 to 346 applied during the reduction control period may be called the reduction control mode. When the reduction control period of a predetermined time ends, the CPU 350 shifts the control mode of the fixing device 120 from the reduction control mode to the temperature control mode. In the temperature control mode, the duty is adjusted based on the detection result of the temperature of the fixing device 120. Thereby, the temperature of the fixing device 120 is maintained at the target temperature.

[0037] [Function of CPU] FIG. 6 shows the functions realized by the CPU 350 executing the control program. The acquisition unit 601 acquires from the voltage detection circuit 301 the detection result (maximum value) of the AC voltage supplied from the first commercial power supply 151. The acquisition unit 601 may determine the effective value or the nominal voltage of the AC voltage of the first commercial power supply 151 from the detection result. The acquisition unit 601 acquires from the voltage detection circuit 302 the detection result (maximum value) of the AC voltage supplied from the second commercial power supply 152. The acquisition unit 601 may determine the effective value or the nominal voltage of the AC voltage of the second commercial power supply 152 from this detection result. Alternatively, the acquisition unit 601 may accept user input of the nominal voltage of the AC voltage of the first commercial power supply 151 and the nominal voltage of the AC voltage of the second commercial power supply 152 from the operation unit 390.

[0038] The determination unit 602 determines the duty applied to the first heater group 361 during the reduction control period based on the AC voltage (maximum value, effective value, or nominal voltage) of the first commercial power supply 151. The determination unit 602 determines the duty applied to the second heater group 362 during the reduction control period based on the AC voltage (maximum value, effective value, or nominal voltage) of the second commercial power supply 152. During the reduction control period, the setting unit 603 sets the duty determined by the determination unit 602 to the energization control unit 604. The energization control unit 604 performs energization control for the heaters 341~ 346 with reference to the rising edge of the zero-crossing signal. Since power is supplied to the heaters 341~343 from the first commercial power supply 151, a duty corresponding to the AC voltage of the first commercial power supply 151 is applied to the heaters 341~343. Since power is supplied to the heaters 344~346 from the second commercial power supply 152, a duty corresponding to the AC voltage of the second commercial power supply 152 is applied to the heaters 344~346.

[0039] When the reduction control period ends, the CPU 350 starts temperature control. During the temperature control period, the temperature adjustment unit 606 determines the duty so that the temperatures detected by the temperature sensors 131 and 132 approach the target temperature. The duty of the heaters 341 and 346 responsible for heating the central region may be determined based on the detection result of the temperature sensor 131. The duty of the heaters 343, 344, and 345 responsible for heating the end regions may be determined based on the detection result of the temperature sensor 132. The duty of the heater 342 responsible for heating both the end regions and the central region may be determined based on the average value of the detection results of the temperature sensors 131 and 132. The setting unit 603 sets the duty determined by the temperature adjustment unit 606 to the energization control unit 604. The energization control unit 604 performs energization control for the heaters 341~346 with the duty determined by the temperature adjustment unit 606.

[0040] The timer 605 is used for monitoring each control period and monitoring the energization start timing based on the zero-cross signal. The duty table 611 stored in the memory 360 holds the duty corresponding to the AC voltage (maximum value, effective value, or nominal voltage). The determination unit 602 may determine the duty by referring to the duty table 611 based on the AC voltage (maximum value, effective value, or nominal voltage) acquired by the acquisition unit 601. Instead of the duty table 611, an arithmetic function that takes the AC voltage (maximum value, effective value, or nominal voltage) as an input and outputs the duty may be used. The temperature table 612 is used to determine the duty from the difference (temperature difference) between the detection result of the fixing device 120 and the target temperature. That is, the temperature table 612 holds the correspondence between the temperature difference and the duty. The temperature adjustment unit 606 acquires the duty corresponding to the temperature difference from the temperature table 612. Instead of the temperature table 612, an arithmetic function that takes the temperature difference as an input and outputs the duty may be used. The period table 613 stores the reduction control period corresponding to the AC voltage (maximum value, effective value, or nominal voltage). The period table 613 will be described in detail in the second embodiment.

[0041] The duty table 611, the temperature table 612, and the period table 613 may be provided individually for the heaters 341 to 346. This is because, as shown in FIGS. 4(A) and 4(B), the heat generation capabilities of the heaters 341 to 346 are different from each other. That is, for the same voltage information, the duty and the reduction control period of the heaters 341 to 346 may be different from each other.

[0042] [Flowchart] FIG. 7 is a flowchart showing the energization control method of the fixing device 120. When the image forming apparatus 100 is activated, the CPU 350 executes the following processes according to the control program. Here, the energization control method of the heater 341 will be described, but the same energization control method is applied to each of the heaters 342 to 346.

[0043] In S701, the CPU 350 determines whether the start condition is satisfied. The start condition is a condition for starting the heating of the fixing device 120. Examples of the start condition include that the image forming apparatus 100 has been started, or that a print job has been received from the operation unit 390 or the host computer. When the start condition is satisfied, the CPU 350 advances the process to S702. If the start condition is not satisfied, the CPU 350 (power supply control unit 604) outputs a control signal 331 to the switch 321 such that the switch 321 is turned off.

[0044] In S702, the CPU 350 (acquisition unit 601) acquires the AC voltage (maximum value, effective value, or nominal voltage) of the first commercial power supply 151 that supplies power to the heater 341. For example, the acquisition unit 601 acquires the AC voltage (maximum value, effective value, or nominal voltage) based on the detection signal of the voltage detection circuit 301. Alternatively, the acquisition unit 601 may acquire the AC voltage (maximum value, effective value, or nominal voltage) based on the information input through the operation unit 390. The nominal voltage may also be called the nominal value. The maximum value or the effective value may also be called the measured value or the actual measured value.

[0045] In S703, the CPU 350 (determination unit 602) determines the duty (on-time angle) applied to the heater 341 during the reduction control period. The determination unit 602 determines the duty based on the AC voltage (maximum value, effective value, or nominal voltage) acquired by the acquisition unit 601. The setting unit 603 sets the determined duty to the power supply control unit 604.

[0046] In S704, the CPU 350 (power supply control unit 604) determines whether a zero cross is detected. The power supply control unit 604 detects the zero cross based on the zero cross signal output from the voltage detection circuit 301. When a zero cross is detected, the CPU 350 advances the process to S705.

[0047] In S705, the CPU 350 (power supply control unit 604) starts flicker reduction control. As a result, the inrush current is reduced and the flicker is also reduced. The power supply control unit 604 turns on the switch 321 at the power supply start timing (e.g., time t2) that is delayed by a predetermined time from the timing (e.g., time t0) when the zero crossing is detected. The predetermined time is determined based on the duty. In the case of FIG. 5(A), the predetermined time is the difference between the zero crossing cycle and the duty. The power supply control unit 604 determines whether the power supply start timing has arrived by monitoring the predetermined time using the timer 605.

[0048] In S706, the CPU 350 (setting unit 603) determines whether the reduction control period has ended. In the first embodiment, the reduction control period is a fixed value stored in the memory 360. The setting unit 603 determines whether the reduction control period has ended using the timer 605. If the reduction control period has not ended, the CPU 350 advances the process to S707. In S707, the CPU 350 (power supply control unit 604) continues the flicker reduction control. On the other hand, if the reduction control period has ended, the CPU 350 advances the process to S708.

[0049] In S708, the CPU 350 (setting unit 603) shifts the control of the fixing device 120 from the flicker reduction control (reduction control mode) to the temperature control (temperature control mode). In the temperature control mode, the temperature adjustment unit 606 determines the duty corresponding to the difference between the temperature acquired by the temperature sensor 131 and the target temperature. The setting unit 603 sets the duty determined by the temperature adjustment unit 606 to the power supply control unit 604.

[0050] In S709, the CPU 350 (setting unit 603) determines whether the stop condition is satisfied. The stop condition is a condition for stopping the supply of power to the fixing device 120. For example, when the image forming apparatus 100 finishes forming an image (print job), the CPU 350 starts the timer 605. If no next print job is input before the timer 605 measures a predetermined time (that is, when the timer 605 times out), the setting unit 603 sets the duty to zero. As a result, the fixing device 120 shifts from the operating state to the power saving state. On the other hand, if the stop condition is not satisfied, the CPU 350 advances the process to S710. In S710, the CPU 350 (power supply control unit 604) continues temperature control. That is, the temperature adjustment unit 606 determines a duty corresponding to the difference between the temperature acquired by the temperature sensor 131 and the target temperature. The setting unit 603 sets the duty determined by the temperature adjustment unit 606 to the power supply control unit 604. The power supply control unit 604 turns on / off the switch 321 with the duty determined by the temperature adjustment unit 606. As a result, the temperature of the fixing device 120 is maintained at the target temperature.

[0051] As described above, according to the first embodiment, the duty is determined according to the AC voltage (voltage value) of the AC power supply. If the AC voltage is high, a small duty is set. If the AC voltage is low, a large duty is set. Therefore, efficient heating is realized while reducing flicker according to the effective value of the AC voltage. The effective value of the AC voltage, the maximum value of the AC voltage, and the nominal value (nominal voltage) are correlated with each other. Therefore, any of the effective value of the AC voltage, the maximum value, or the nominal voltage may be used to determine the duty. However, if the measured value of the effective value or the maximum value of the AC voltage is used, it becomes possible to accurately determine the duty even in a region where the nominal voltage deviates from the effective value or the maximum value.

[0052] In Example 1, since there are two power supply systems, the duty is determined for each power supply system. However, the technical idea of Example 1 is also applicable to the case where the fixing device 120 is connected to a single power supply system. In this case, the duty of each of the heaters 341 to 346 is determined based on the AC voltage of the single power supply system.

[0053] In Example 1, six heaters 341 to 346 are illustrated, but the technical idea of Example 1 does not depend on the number of heaters. That is, Example 1 is also applicable to a single heater. In Fig. 5(C), the maximum value is detected as the measured value of the AC voltage, but this is only an example. The effective value or the average value may be measured instead of the maximum value.

[0054] In Example 1, the duty is a constant value during the reduction control period. However, the duty may be variably controlled. For example, the duty may be gradually increased during the reduction control period. Thereby, the heating time will be shortened. Note that the reduction control period may be called a slow start period or a soft start period.

[0055] <Example 2> In Example 1, the duty of each heater is set according to the AC voltage. However, this is only an example. By setting the reduction control period according to the AC voltage, the inrush current can be reduced, and as a result, the flicker may be reduced. Specifically, the reduction control period of the first heater group 361 is set according to the AC voltage (maximum value, effective value, or nominal voltage) of the first commercial power supply 151. The reduction control period of the second heater group 362 is set according to the AC voltage (maximum value, effective value, or nominal voltage) of the second commercial power supply 152. For the description of matters common or similar to those in Example 1 in Example 2, the description of Example 1 is incorporated by reference.

[0056] FIG. 8(A) shows the changes in control signals 331 to 336. FIG. 8(B) shows the changes in the input current I1 input from the first commercial power supply 151 and the changes in the input current I2 input from the second commercial power supply 152. FIG. 8(C) shows the changes in the input voltage V1 input from the first commercial power supply 151 and the changes in the input voltage V2 input from the second commercial power supply 152. Here, it shows that the maximum value of the input voltage V1 is larger than the maximum value of the input voltage V2. That is, it shows that the nominal voltage (rms value) of the first commercial power supply 151 is higher than the nominal voltage (rms value) of the second commercial power supply 152. FIG. 8(D) shows the zero-cross signals for the first commercial power supply 151 and the second commercial power supply 152.

[0057] As shown in FIG. 8(A), the reduction control period of the first heater group 361 is T1. The reduction control period of the second heater group 362 is T2. The reduction control period T1 is determined, for example, based on the detection signal 381 shown in FIG. 8(C). The reduction control period T2 is determined, for example, based on the detection signal 382 shown in FIG. 8(C). As shown in FIG. 8(C), the input voltage V1 from the first commercial power supply 151 is higher than the input voltage V2 from the second commercial power supply 152. Therefore, the reduction control period T2 of the second heater group 362 is shorter than the reduction control period T1 of the first heater group 361. That is, because the reduction control period T2 of the second heater group 362 is short, it is possible to increase the power supply amount to the second heater group 362 earlier. Thereby, the heating time required for the temperature of the fixing device 120 to reach the target temperature is shortened.

[0058] As shown in FIG. 8(B), the duty applied to the first heater group 361 during the reduction control period T1 is equal to the duty applied to the second heater group 362 during the reduction control period T2. This is because flicker is reduced by the reduction control periods T1 and T2.

[0059] As shown in FIG. 8(A), the reduction control period T1 is the period from time t0 to time t3. The reduction control period T2 is the period from time t0 to time t2. The energization control unit 604 starts the reduction control based on the rising timing (time t0) of the zero-cross signal. The energization control unit 604 controls the duty in each cycle of the reduction control periods T1 and T2 to be constant.

[0060] [Flowchart] FIG. 9 is a flowchart showing the energization control method of the fixing device 120. When the image forming apparatus 100 is activated, the CPU 350 executes the following processes according to the control program. Here, the energization control method of the heater 341 will be described, but the same energization control method is applied to each of the heaters 342 to 346. Note that, compared with the first embodiment, in the second embodiment, the reduction control periods T1 and T2 are variable according to the AC voltage, and the initial values of the duty in the reduction control periods T1 and T2 are constant, which is different. Therefore, in FIG. 9, the point where S703 is replaced by S903 is different. Therefore, hereinafter, S903 will be mainly described.

[0061] In S903, the CPU 350 (determination unit 602) determines the reduction control period T1 based on the AC voltage (maximum value, effective value, or nominal voltage) acquired by the acquisition unit 601. The voltage information indicating the AC voltage is acquired through the voltage detection circuit 301 or the operation unit 390. Note that the voltage information used to determine the reduction control period T2 is acquired from the voltage detection circuit 302 or the operation unit 390. The determination unit 602 may determine the reduction control periods T1 and T2 corresponding to the voltage information by referring to the period table 613 stored in the memory 360. Alternatively, an arithmetic function that takes the voltage information as an input and outputs the reduction control periods T1 and T2 may be used. The setting unit 603 sets the reduction control periods T1 and T2 in the energization control unit 604. In S706 after that, the reduction control periods T1 and T2 determined and set in S903 are monitored.

[0062] In Example 2, the duty in the reduction control periods T1 and T2 is maintained constant with respect to the voltage of the commercial AC power supply, and only the reduction control periods T1 and T2 are variable, but this is only an example. The variable control of the duty described in Example 1 may be combined with Example 2. That is, both the duty in the reduction control periods T1 and T2 and the reduction control periods T1 and T2 may be determined according to the voltage of the commercial AC power supply. That is, the duty may be a constant value determined according to the voltage of the commercial AC power supply. Also, the duty in the reduction control periods T1 and T2 may be variably controlled. For example, the duty in the reduction control periods T1 and T2 may be gradually increased from an initial value. However, the initial value is determined according to the voltage of the commercial AC power supply as described in Example 1.

[0063] Here, there are two power supply systems such as the first commercial power supply 151 and the second commercial power supply 152, but this is only an example. Example 2 is also applicable when power is supplied to the heaters 341 to 346 from a single power supply system. That is, the reduction control periods T1 and T2 may be determined according to the voltage information of the single power supply system. However, in this case, T1 = T2 will hold. Here, six heaters 341 to 346 are illustrated, but Example 2 is applicable as long as the number of heaters is one or more. In Fig. 8(C), the maximum value of the AC voltage is used as the voltage information, but as described above, the effective value, the average value, the nominal voltage, etc. may be used. <Technical idea derived from the embodiment> [Viewpoint 1, 16] The voltage detection circuit 301, the operation unit 390, and the acquisition unit 601 are examples of first acquisition means for acquiring first voltage information indicating the voltage value of the AC voltage supplied from the first AC power source. The fixing device 120 has a first heating element that generates heat by the power supplied from the first AC power source, and is an example of fixing means for fixing a toner image on a sheet using the heat. The switch 321 is an example of a first switch provided between the first AC power source and the first heating element. The CPU 350 controls the first switch so that the power from the first AC power source is intermittently supplied to the first heating element from the timing when the supply of power from the first AC power source to the first heating element starts until the timing when the first predetermined time has elapsed, which is an example of control means. Further, the CPU 350 is an example of control means for performing energization control to make it difficult for an inrush current from the first AC power source to flow to the first heating element for the first predetermined time after starting the supply of power from the first AC power source to the first heating element. As described in the first embodiment, the CPU 350 may determine the on-time (e.g., duty) of the first switch per half cycle of the AC of the first AC power source applied to the first switch based on the first voltage information at the first predetermined time. As described in the second embodiment, the CPU 350 may determine the length of the first predetermined time (reduction control period T1) based on the first voltage information. Alternatively, the CPU 350 may determine both the on-time (e.g., duty) of the first switch and the length of the first predetermined time (reduction control period T1) based on the first voltage information. Thereby, flicker is reduced according to the effective value of the AC voltage, and efficient heating is realized.

[0064] [Aspect 2] The voltage detection circuit 302, the operation unit 390, and the acquisition unit 601 are an example of second acquisition means for acquiring second voltage information indicating the voltage value of the AC voltage supplied from the second AC power supply. The heater 344 is an example of a second heating element provided in the fixing means and generating heat by the power supplied from the second AC power supply. The switch 324 is an example of a second switch provided between the second AC power supply and the second heating element. After starting to supply power from the second AC power supply to the second heating element, the CPU 350 executes energization control to make it difficult for the inrush current from the second AC power supply to the second heating element to flow over a second predetermined time. The CPU 350 may determine the on-time of the second switch per half cycle of the AC of the second AC power supply applied to the second switch based on the second voltage information at the second predetermined time. The CPU 350 may determine the length of the second predetermined time (e.g., reduction control period T2) based on the second voltage information. Further, the CPU 350 may determine both the on-time (e.g., duty) of the second switch and the length of the second predetermined time (reduction control period T2) based on the second voltage information. Thus, even in a case where power is supplied from a plurality of AC power supplies to a plurality of heaters, flicker is reduced according to the voltage value (effective value, etc.) of the AC voltage, and efficient heating is realized. As a result, since the length of the reduction control period T2 becomes a length corresponding to the AC voltage of the second AC power supply, the time required to control the temperature of the fixing device 120 to the target temperature will be shortened.

[0065] [Viewpoints 3, 4] The first voltage information may include any one of the maximum value, effective value, average value, or nominal value of the AC voltage supplied from the first AC power supply. The second voltage information may include any one of the maximum value, effective value, average value, or nominal value of the AC voltage supplied from the second AC power supply. In particular, when the measured values by the voltage detection circuits 301 and 302 are used, it is possible to adjust the length of the reduction control period or the duty in the reduction control period even for short-term fluctuations of the AC power supply. When there are few short-term fluctuations in the short-term AC voltage, the nominal voltage input by the user may be used. For example, when an AC voltage of 240V, which is the nominal voltage, is stably supplied, 240V may be used as the voltage information. Alternatively, when the voltage (effective value) of the first AC power supply is 264V (nominal voltage + 10%) and the voltage (effective value) of the second AC power supply is 216V (nominal voltage - 10%), the duty and the reduction control period may be determined according to the respective voltages (measured values).

[0066] [Aspect 5] As shown in FIG. 5(A), since the duty of the first heating element and the duty of the second heating element are different, the timing at which the first heating element turns on and the timing at which the second heating element turns on may be shifted. Alternatively, even if the duty of the first heating element and the duty of the second heating element are the same, the timing at which the first heating element turns on and the timing at which the second heating element turns on may be shifted. For example, when the first AC power supply and the second AC power supply are the same AC power supply, the first heating element and the second heating element are supplied with power from a single AC power supply. When the first heating element and the second heating element turn on simultaneously, the voltage drop of the single AC power supply increases and the flicker increases. Here, an increase in flicker means an increase in flicker that can be felt by humans. Therefore, by shifting the timing at which the first heating element turns on and the timing at which the second heating element turns on, the flicker is reduced.

[0067] [Aspects 6 - 9] The temperature sensors 131 and 132 function as detection means for detecting the temperature of the fixing means. The control mode for determining the on-time of the first switch for each half-cycle of the alternating current of the first AC power supply based on the first voltage information may be called the reduction control mode. In the reduction control mode, the first switch is turned on only for a time (on-time) shorter than the half-cycle of the alternating current. The control mode for determining the on-time of the first switch for each half-cycle of the alternating current of the first AC power supply based on the detection result of the detection means may be called the temperature control mode. As described in the first embodiment, in the reduction control mode, the on-time of the first switch may be constant. The CPU 350 may gradually increase the on-time of the first switch from the initial value in the reduction control mode. Here, the initial value may be determined based on the first voltage information. The on-time of the first switch in the reduction control mode may have a negative correlation with the peak value (maximum value) or the effective value of the alternating voltage of the first AC power supply. That is, the higher the effective value of the alternating voltage of the first AC power supply, the more likely a large inrush current is to occur. Therefore, by determining the on-time of the first switch so as to have a negative correlation with the effective value of the alternating voltage, the inrush current is reduced and the flicker is also reduced.

[0068] [Viewpoints 10, 11] The resistance value of the first heating element may increase in correlation with the temperature of the first heating element. That is, it is necessary to reduce the inrush current during the period when the temperature of the first heating element is low. The first heating element may be a halogen heater. Note that this embodiment will be useful for any heating element whose resistance value correlates with the temperature of the heating element. That is, this embodiment is also effective for heating elements other than halogen heaters.

[0069] [Viewpoint 12] The heater 342 is an example of a third heating element provided in the fixing means and generating heat by the electric power supplied from the first AC power supply. The switch 322 is an example of a third switch provided between the first AC power supply and the third heating element. After starting the supply of electric power from the first AC power supply to the third heating element, the CPU 350 executes energization control to make it difficult for an inrush current from the first AC power supply to the third heating element to flow over a third predetermined time. The CPU 350 may determine at least one of the on-time of the third switch per half cycle of the alternating current of the first AC power supply applied to the third switch at the third predetermined time and the length of the third predetermined time based on the first voltage information.

[0070] [Aspect 13] The heater 343 is an example of a fourth heating element provided in the fixing means and generating heat by the electric power supplied from the first AC power supply. The switch 323 is an example of a fourth switch provided between the first AC power supply and the fourth heating element. After starting the supply of electric power from the first AC power supply to the fourth heating element, the CPU 350 executes energization control to make it difficult for an inrush current from the first AC power supply to the fourth heating element to flow over a fourth predetermined time. The CPU 350 may determine at least one of the on-time of the third switch per half cycle of the alternating current of the first AC power supply applied to the fourth switch at the fourth predetermined time and the length of the fourth predetermined time based on the first voltage information.

[0071] [Aspect 14] The heater 345 is an example of a fifth heating element provided in the fixing means and generating heat by the electric power supplied from the second AC power supply. The switch 325 is an example of a fifth switch provided between the second AC power supply and the fifth heating element. After starting the supply of electric power from the second AC power supply to the fifth heating element, the CPU 350 executes energization control to make it difficult for an inrush current from the second AC power supply to the fifth heating element to flow over a fifth predetermined time. The CPU 350 may determine at least one of the on-time of the third switch per half cycle of the alternating current of the second AC power supply applied to the fifth switch at the fifth predetermined time and the length of the fifth predetermined time based on the second voltage information.

[0072] [Aspect 15] The heater 346 is an example of a sixth heating element provided in the fixing means and generating heat by the electric power supplied from the second AC power supply. The switch 326 is an example of a sixth switch provided between the second AC power supply and the sixth heating element. After starting to supply electric power from the second AC power supply to the sixth heating element, the CPU 350 executes energization control to make it difficult for the inrush current from the second AC power supply to flow to the sixth heating element for a sixth predetermined time. The CPU 350 may determine at least one of the on-time of the third switch per half cycle of the AC of the second AC power supply applied to the sixth switch at the sixth predetermined time and the length of the sixth predetermined time based on the second voltage information.

[0073] The invention is not limited to the above embodiments, and various changes and modifications are possible without departing from the spirit and scope of the invention. Therefore, claims are attached to disclose the scope of the invention.

Explanation of Reference Numerals

[0074] 301, 302: Voltage detection circuit, 431 to 436: Heater, 321 to 326: Switch, 350: CPU

Claims

1. Image forming means for forming an image on a sheet; Fixing means for fixing the image on the sheet, the fixing means having a first heating element that generates heat by electric power supplied from a first AC power source and a second heating element that generates heat by electric power supplied from a second AC power source different from the first AC power source; Voltage detection means for detecting the value of a first AC voltage supplied from the first AC power source and the value of a second AC voltage supplied from the second AC power source; Temperature detection means for detecting the temperature of the fixing means; Power supply means for supplying power to the fixing means; An image forming apparatus comprising control means for controlling the power supply means based on the detection result of the temperature detection means; After the image forming apparatus is powered on, the control means, during a startup operation of starting to supply power to the first heating element and the second heating element to raise the temperature of the fixing means to a predetermined target temperature, (i) A reduction control mode in which, until a first predetermined period has elapsed after starting to supply power to the first heating element, the duty ratio of energizing the first heating element is limited to a predetermined first predetermined duty ratio, and until a second predetermined period has elapsed after starting to supply power to the second heating element, the duty ratio of energizing the second heating element is limited to a predetermined second predetermined duty ratio to supply power; (ii) After the first predetermined period has elapsed after starting to supply power to the first heating element, the limitation of the duty ratio of energizing the first heating element to the first predetermined duty ratio is released, and after the second predetermined period has elapsed after starting to supply power to the second heating element, the limitation of the duty ratio of energizing the second heating element to the second predetermined duty ratio is released, and based on the temperature of the fixing means, a temperature control mode for controlling the duty ratio of energizing the first heating element and the second heating element is executable. After the image forming apparatus is powered on and before executing the reduction control mode, the control means detects values of the first AC voltage supplied from the first AC power source and the second AC voltage supplied from the second AC power source by the voltage detection means, determines the first predetermined duty ratio of the first heating element when the first heating element is first turned on after the image forming apparatus is powered on based on the value of the first AC voltage, and determines the second predetermined duty ratio of the second heating element when the second heating element is first turned on after the image forming apparatus is powered on based on the value of the second AC voltage, and is configured as such. An image forming apparatus characterized by the above.

2. In the reduction control mode, the control means controls to supply power to the first heating element at the first predetermined duty ratio predetermined based on the value of the first AC voltage, and controls to supply power to the second heating element so that the duty ratio of energizing the second heating element becomes the second predetermined duty ratio different from the first predetermined duty ratio based on the value of the second AC voltage. The image forming apparatus according to claim 1, characterized by the above.

3. During execution of the reduction control mode, the first predetermined duty ratio is preset to gradually increase with time. The image forming apparatus according to claim 1, characterized by the above.

4. The control means is configured to change the first predetermined period for the first heating element based on a detection result of detecting the value of the first AC voltage supplied from the first AC power source by the voltage detection means. The image forming apparatus according to claim 1, characterized by the above.

Images