Image forming device

Abstract

To improve a long-term flicker in a waiting time of an image formation device.SOLUTION: A first heater and a second heater connected to different power source systems heat a heat transfer medium. An image formation device makes the first heater and the second heater operate in turn in a waiting time to maintain the temperature of the heat transfer medium to a waiting temperature. In a direction in which the first heater extends, heating ability of the middle of the first heater may be at least heating ability of the end part of the first heater. In a direction in which the second heater extends, the heating ability of the end part of the second heater may be at least heating ability of the middle of the second heater.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus having a fixing device. [Background technology]

[0002] In an electrophotographic image forming apparatus, a fixing device uses heat and pressure to fix a toner image to a sheet. The fixing device has a heater for heating the sheet and the toner image. Patent Document 1 describes a fixing device equipped with a halogen heater. In order to maintain good fixability of the toner image to the sheet, it is necessary to appropriately control the heater temperature. This temperature control is achieved by turning the heater on and off. However, it has been pointed out that turning the heater on and off can cause a flicker phenomenon (Patent Document 2). The flicker phenomenon refers to a phenomenon in which the voltage of an AC power supply fluctuates due to inrush currents generated in electrical equipment connected to the AC power supply, affecting the operation of other equipment connected to the AC power supply. A typical example of the flicker phenomenon is the flickering of lighting devices. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-021173 [Patent Document 2] Japanese Patent Application Publication No. 2018-146712 Summary of the Invention [Problem to be solved by the invention]

[0004] The International Electrotechnical Commission (IEC) standard (IEC61000-3-3) defines two indicators (flicker values) that indicate the degree of flicker: the short-term flicker value (Pst value) and the long-term flicker value (Plt value). The Pst value indicates the degree of flicker measured over a 10-minute period. A Pst value of 1 is defined as flicker that 50% of people find unpleasant. The IEC standard also defines a Pst value of 1 or less as the standard value. On the other hand, the Plt value is calculated by taking the cube mean of the Pst value measured 12 times (over 2 hours). The IEC standard also defines a Plt value of 0.65 or less as the standard value. Image forming devices are required to have a Pst value of 1 or less during image formation operation and a Plt value of 0.65 or less during standby.

[0005] However, it takes a considerable amount of time for a heater, which consumes a lot of power, to heat up from the ambient temperature to the target fixing temperature. Therefore, by preheating the heater during standby, the time required to heat the heater to the target temperature can be reduced. However, controlling the heater temperature during standby can sometimes worsen long-term flicker. Therefore, an object of the present invention is to improve long-term flicker during standby periods in image forming apparatuses. [Means for solving the problem]

[0006] The present invention is, for example, an image forming means for forming an image on a sheet; A fixing unit for fixing the image to the sheet, a first heater that generates heat when a first current is supplied from a first power source, the first heater having a first region capable of generating heat and a second region capable of generating heat at a position different from the first region in a longitudinal direction of the first heater, the first region having a higher heat generating capacity than the second region; a first switch disposed between the first heater and the first power source, the first switch switching whether or not the first current is supplied to the first heater; a second heater that generates heat when a second current is supplied from a second power source different from the first power source, wherein a heat generation distribution characteristic of the second heater in a longitudinal direction of the second heater is different from a heat generation distribution characteristic of the first heater in the longitudinal direction of the first heater, the second heater having a third region capable of generating heat and a fourth region capable of generating heat at a position different from the third region in the longitudinal direction of the second heater, and wherein the heat generation capacity of the third region is lower than that of the fourth region; a third heater that generates heat when a third current is supplied from the first power source; a fourth heater that generates heat when a fourth current is supplied from the second power source; the first region of the first heater overlaps with the third region of the second heater; the second region of the first heater overlaps with the fourth region of the second heater; a fixing unit including a second switch disposed between the second heater and the second power source, the second switch switching whether or not the second current is supplied to the second heater; a control means; The control means In an image forming mode in which the image is formed on the sheet, the first switch and the second switch are controlled so that the temperature of the fixing means is maintained at a fixing temperature for fixing the image on the sheet; In a standby mode in which the image is not formed on the sheet, interrupting the third current supplied to the third heater and interrupting the fourth current supplied to the fourth heater; An image forming apparatus is provided, characterized in that the first switch and the second switch are controlled so that the temperature of the fixing means is maintained at a standby temperature in the standby mode, and the first switch and the second switch are controlled so that the period during which the first current flows to the first heater and the period during which the second current flows to the second heater do not overlap. [Effects of the Invention]

[0007] According to the present invention, long-term flicker during standby periods of an image forming apparatus is improved. [Brief explanation of the drawings]

[0008] [Figure 1]FIG. 1 is a diagram illustrating an image forming apparatus. [Figure 2] FIG. 1 is a diagram illustrating a fixing device. [Figure 3] A diagram illustrating a heating roller [Figure 4] Diagram explaining the heater's heat generation capacity [Figure 5] Diagram explaining the control board [Figure 6] Diagram explaining long-term flicker [Figure 7] Diagram explaining how to improve long-term flicker [Figure 8] Flowchart showing a control method according to the first embodiment [Figure 9] FIG. 10 is a diagram for explaining a method for improving long-term flicker in the second embodiment. [Figure 10] Flowchart showing a control method according to the second embodiment [Figure 11] Flowchart showing a control method according to the third embodiment [Figure 12] Flowchart showing a control method according to the fourth embodiment DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] Example 1 [Image forming device] As shown in FIG. 1, image forming apparatus 100 is an electrophotographic printer equipped with four image forming stations. Image forming apparatus 100 may be commercialized as a copier, multifunction peripheral, facsimile machine, 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 operation and configuration of the four stations are identical or similar. Therefore, when describing matters common to all four colors, the letters ymck are omitted from the reference numerals. Note that the technical concept of the present invention is also applicable to monochrome printers.

[0011] The photosensitive drum 101 is a photoconductor and image carrier that rotates and carries 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 corresponding to an image signal, forming an electrostatic latent image on the surface of the photosensitive drum 101. The developing device 104 attaches toner to the electrostatic latent image to form a toner image. The primary transfer roller 105 transfers the toner image from the photosensitive drum 101 to the intermediate transfer belt 107. That is, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are transferred to the intermediate transfer belt 107 in order, thereby forming a full-color image. As the intermediate transfer belt 107 rotates, the toner image is transported to a secondary transfer unit. A pair of secondary transfer rollers 109 is provided in the secondary transfer unit.

[0012] The paper feed cassette 111 is a paper feed container that can store a large number of sheets P. The pickup roller 112 sends out the sheets P from the paper feed cassette 111 to the conveyance path. The paper feed roller 113 conveys the sheets P further downstream while preventing double feeding of the sheets P. "Downstream" means downstream in the conveyance direction of the sheets P. The registration roller 114 is a conveyance roller that prevents the sheets P from skewing. The leading edge of the sheets P in the conveyance direction of the sheets P abuts against the registration roller 114, thereby correcting the skew of the sheets P. The sheets P are then conveyed to the secondary transfer unit.

[0013] In the secondary transfer portion, a pair of secondary transfer rollers 109 transfers the toner image from the intermediate transfer belt 107 to the sheet P. A fixing device 120 applies heat and pressure to the sheet P and the toner image to fix the toner image onto the sheet P. Conveying rollers 115, 116, and 117 are arranged downstream of the fixing device 120, and convey the sheet P and pass it to a discharge roller 118. The discharge roller 118 discharges the sheet P to the outside of the image forming apparatus 100 (for example, to a sheet tray).

[0014] [Fusing device] As shown in FIG. 2, the fixing device 120 has a heating unit 200 centered around an endless, rotatable fixing belt 210 serving as a heat transmission medium. In FIG. 2, the Z direction is the height direction, and the X direction is the direction parallel to the conveyance direction of the sheet P. The fixing belt 210 is tensioned between a pad 220, a heating roller 240, and a tension roller 250. The heating roller 240 is a heating rotor having a heater (e.g., a halogen heater) inside. A halogen heater is a heater having a halogen lamp as a heat generating element. The heating roller 240 heats the fixing belt 210. The heating roller 240 rotates by a torque 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 (not shown) of the heating unit 200. The tension of this spring is, for example, 50 N. The tension roller 250 rotates in response to the rotation of the fixing belt 210. The pad 220 supports the inner circumferential surface of the fixing belt 210 with 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 and the pad 220 may be biased by a biasing mechanism (not shown) so that the nip portion N of 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 an inner diameter of, for example, 120 mm. The fixing belt 210 may have a three-layer structure including 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, fluororesin. Examples of fluororesin that can be used include PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin).

[0016] The material of pad 220 is, for example, LCP (liquid crystal polymer) resin. 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. Multiple heaters (for example, six) may be disposed inside the pipe. Heat supplied from the heaters is transmitted from heating roller 240 to fixing belt 210, and further transmitted from fixing belt 210 to sheet P and the toner image. Tension roller 250 may also be formed from 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 a roller having, for example, an elastic layer and a release layer. The elastic layer is provided on the outer periphery of the rotation shaft of the pressure roller 230. Furthermore, a release layer is provided on the outer periphery of the elastic layer. The material of the rotation shaft 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] [Heater placement] FIG. 3 is a schematic cross-sectional view of heating roller 240 taken along a plane parallel to the rotation axis of heating roller 240. Six heaters 341 to 346 are supported by a holder (not shown) provided inside heating roller 240. Thermistors 301 and 302 may be arranged so as to contact the outer circumferential surface of heating roller 240. This makes it possible to measure the surface temperature of heating roller 240 or fixing belt 210 with high accuracy. Thermistor 301 may be arranged at the center of heating roller 240 in the width direction (which may also be referred to as the direction in which heating roller 240 extends (Y direction)). In other words, the Y direction is a direction parallel to the rotation axis of heating roller 240. Thermistor 302 measures the surface temperature at the end of heating roller 240.

[0019] [Heater light distribution (heating capacity)] 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. Fig. 4(B) shows the light distribution of the three heaters 344, 345, and 346 that form the second heater group. The horizontal axis represents the position in the Y direction. The vertical axis represents 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.

[0020] Y0 indicates the position of one end (hereinafter referred to as the left end) of the heaters 341-346. Y3 indicates the position of the other end (hereinafter referred to as the right end) of the heaters 341-346. 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. In other words, the distance from Y1 to Y2 is 250 mm. In this way, the ratio of the length of one end region to the length of the central region may be 1:2.

[0021] Heaters 341 and 346 are heat sources that mainly heat the central region. Heaters 343, 344, and 345 are heat sources that mainly heat the two end regions. Heater 342 is a heat source that heats the entire region, including the central region and the end region, almost uniformly.

[0022] 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 sheet P is transported so that the center of the sheet passes near the center in the Y direction. For example, when a sheet P having a narrow length (width) in the Y direction is continuously transported, the lighting ratio (power-on time) of the heaters 343, 344, and 345, which mainly heat the edge regions, is reduced. This prevents excessive heat accumulation in both edge regions of the heating roller 240.

[0023] 4(A) and 4(B), thermistor 301 is disposed at the center of the central region. Thermistor 302 is disposed at the center of the left edge region. In particular, by disposing thermistors 301 and 302 so as not to overlap with Y1 and Y2, the temperature of the central region (central temperature M) and the temperature of the edge region (edge ​​temperature R) can be accurately detected.

[0024] The ratio of the heat generating capacity of the central region of heater 341 is X%. The ratio of the heat generating capacity of the edge region of heater 341 is Y% (X>Y). Here, it is assumed that the power consumption of heater 341 is 1000 W. Therefore, the heat generating capacity of one edge region of heater 341 is 100 W in terms of power. The heat generating capacity of the central region of heater 341 is 800 W in terms of power. For the remaining heaters 342 to 346, the heat generating capacity of each region can be calculated from the ratio and power consumption shown in FIG. 4(A) or 4(B).

[0025] [controller] As shown in Fig. 5, a control board 500 drives heaters 341 to 346. Power cords 501 and 502 are connected to AC power supplies of different systems. AC power supplied from power cord 501 is supplied to a first heater group 561 via a first power supply system 511. AC power supplied from power cord 502 is supplied to a second heater group 562 via a second power supply system 512. The first heater group 561 includes heaters 341, 342, and 343. The second heater group 562 includes heaters 344, 345, and 346.

[0026] The control board 500 is equipped with a CPU 550 and a plurality of switches 521 to 526. The CPU 550 controls the plurality of switches 521 to 526 in accordance with a control program stored in a memory 560. The memory 560 may include a non-volatile memory (ROM), a volatile memory (RAM), a solid state drive (SSD), a hard disk drive (HDD), and the like.

[0027] Switch 521 is connected between power cord 501 and heater 341 and switches heater 341 on and off in accordance with control signal 531 from CPU 550. Switch 522 is connected between power cord 501 and heater 342 and switches heater 342 on and off in accordance with control signal 532 from CPU 550. Switch 523 is connected between power cord 501 and heater 343 and switches heater 343 on and off in accordance with control signal 533 from CPU 550. Switch 524 is connected between power cord 502 and heater 344 and switches heater 344 on and off in accordance with control signal 534 from CPU 550. Switch 525 is connected between power cord 502 and heater 345 and switches heater 345 on and off in accordance with control signal 535 from CPU 550. The switch 526 is connected between the power cord 502 and the heater 346, and switches the heater 346 on and off in accordance with a control signal 536 from the CPU 550. The switches 521-526 may be switching elements such as triacs, thyristors, transistors, and IGBTs (insulated gate bipolar transistors). However, any switching element can be used as the switches 521-526 as long as it can be controlled by the CPU 550 and has performance (rated voltage, rated current) that matches the power consumption of the heaters 341-346.

[0028] CPU 550 detects the center temperature M of heating roller 240 based on the detection signal output from thermistor 301. CPU 550 detects the end temperature R of heating roller 240 based on the detection signal output from thermistor 302. CPU 550 determines the turn-on ratio (duty ratio) of each of heaters 341-346 based on these temperatures. CPU 550 outputs control signals 531-536 according to the duty ratio of each of heaters 341-346. The duty ratio may be determined, for example, every fixed period (e.g., 10 seconds). Switches 521-526 are switched on / off in units of a time equivalent to two half-waves of the AC power supply (one AC cycle).

[0029] [Anti-flicker] FIGS. 6(A) through 6(D) are diagrams illustrating a state in which long-term flicker is undesirable during the standby period of image forming apparatus 100. FIG. 6(A) shows central temperature M detected by thermistor 301 and edge temperature R detected by thermistor 302. FIG. 6(B) shows control signals 531 and 535. Control signals 532 through 534 and 536 are all assumed to be off. FIG. 6(C) shows the voltage of first power supply system 511. FIG. 6(D) shows the voltage of second power supply system 512. In FIGS. 6(A) through 6(D), the horizontal axis represents time.

[0030] The image forming apparatus 100 has an image formation period (image formation mode) in which an image is formed on the sheet P, and a standby period (standby mode) in which no image is formed. The standby period (standby mode) is provided to reduce the power consumption of the image forming apparatus 100. The fixing belt 210 is preheated during the standby period. This is to raise the temperature of the fixing belt 210 to a target temperature (a temperature at which a toner image can be fixed) in a shorter time when transitioning from the standby period to the image formation period. The temperature of the fixing belt 210 during the standby period may also be called a preheating temperature or a standby temperature. The standby temperature is set lower than the target temperature. The closer the standby temperature is to the target temperature, the shorter the time it takes for the fixing belt 210 to reach the target temperature. However, the closer the standby temperature is to the target temperature, the smaller the effect of reducing power consumption. Therefore, the standby temperature is designed taking these trade-offs into consideration.

[0031] In this way, the total power consumption of the heaters 341 to 346 during the standby period is less than the total power consumption of the heaters 341 to 346 during the image formation period. Therefore, if only the heater 341, which mainly heats the central region, and the heater 345, which mainly heats the edge region, are operated, the standby temperature (e.g., 150°C) can be achieved. Note that the standby temperature may be managed as a predetermined temperature range (e.g., 145°C or higher and 155°C or lower) defined by an upper limit temperature (e.g., 145°C) and a lower limit temperature (e.g., 155°C).

[0032] In FIG. 6A, central temperature M is the temperature obtained by converting the detection value (resistance value) of thermistor 301 into a temperature by CPU 550. Edge temperature R is the temperature obtained by converting the detection value of thermistor 302 into a temperature by CPU 550. Time T1 is the timing when central temperature M falls below 145° C. as a result of all heaters 341 to 346 being turned off. As shown in FIG. 6B, at time T1, CPU 550 switches control signals 531 and 535 from off (low) to on (high) to turn on heaters 341 and 345. As a result, switches 521 and 525 are switched from off to on, and power is supplied to heaters 341 and 345.

[0033] Time T2 is the timing when central temperature M exceeds 155° C. At time T2, CPU 550 switches control signals 531 and 535 to Low to turn off heaters 341 and 345. This switches switches 521 and 525 from ON to OFF, and the supply of power to heaters 341 and 345 is stopped.

[0034] By repeatedly turning the heaters 341 and 345 on and off in this manner, the edge temperature R and the center temperature M are maintained at the standby temperature (e.g., 150°C). The heaters 341 and 345 are repeatedly turned on and off simultaneously. The temperature rise slope when the heaters are turned on and the temperature fall slope when the heaters are turned off become steeper. In other words, the turn-on period of the heater 341 and the turn-on period of the heater 345 become shorter. As shown in FIG. 6(C), the voltage level of the first power supply system 511 fluctuates depending on the timing of turning the heater 341 on and off. As shown in FIG. 6(D), the voltage level of the second power supply system 512 also fluctuates depending on the timing of turning the heater 345 on and off. If this fluctuation occurs frequently, flickering worsens.

[0035] 7(A) to 7(D) are diagrams illustrating measures to improve long-term flicker during standby periods of image forming apparatus 100. FIG. 7(A) shows center temperature M detected by thermistor 301 and edge temperature R detected by thermistor 302. FIG. 7(B) shows control signals 531 and 535. Control signals 532 to 534 and 536 are all assumed to be off. FIG. 7(C) shows the voltage of first power supply system 511. FIG. 7(D) shows the voltage of second power supply system 512. In FIGS. 7(A) to 7(D), the horizontal axis represents time.

[0036] 7(A) and 7(B), time T3 is the timing when central temperature M exceeds the upper limit temperature (155°C) while heater 341 is on and heaters 342 to 346 are off. When central temperature M exceeds the upper limit temperature, CPU 550 generates control signals 531 and 535 so that heater 341 is turned off and heater 345 is turned on. That is, as shown in FIG. 7(B), at time T3, control signal 531 switches from High to Low, and control signal 535 switches from Low to High.

[0037] At time T4, the end temperature R exceeds the upper limit temperature (155° C.). Therefore, the CPU 550 switches the control signals 531 and 535 so that the heater 345 is turned off and the heater 341 is turned on. As shown in FIG. 7B, at time T4, the control signal 531 switches from low to high, and the control signal 535 switches from high to low.

[0038] In this way, when the central temperature M exceeds the upper limit temperature, the CPU 550 turns off the heater 341 and turns on the heater 345. Also, when the end temperature R exceeds the upper limit temperature, the CPU 550 turns on the heater 341 and turns off the heater 345. By repeating this switching control by the CPU 550, the end temperature R and the central temperature M are maintained at the standby temperature (150°C±5°C).

[0039] By repeatedly turning the heaters 341 and 345 on and off alternately, the slope of the temperature rise due to lighting and the slope of the temperature fall due to lighting become gentler. In other words, the lighting periods of the heaters 341 and 345 become longer. As shown in FIG. 7(C), the number of voltage fluctuations in the first power supply system 511 decreases. As shown in FIG. 7(D), the number of voltage fluctuations in the second power supply system 512 also decreases. This improves long-term flickering during standby periods.

[0040] Heater 341 receives power from power cord 501, and heater 345 receives power from power cord 502. That is, heaters 341 and 345 are connected to AC power supplies of different systems. Therefore, the flicker cycle is longer in Example 1 compared to when heaters 341 and 345 are connected to a single power cord.

[0041] [flowchart] 8 shows a control method for fixing device 120 executed by CPU 550. CPU 550 executes the following processes in accordance with a control program. Here, the control modes of CPU 550 or the operation modes of image forming apparatus 100 include an image formation mode and a standby mode. The image formation mode is a mode in which image forming apparatus 100 can perform image formation. The standby mode is a mode in which image forming apparatus 100 cannot perform image formation, and may also be called a power saving mode.

[0042] In S801, the CPU 550 determines whether a standby condition is satisfied. The standby condition is a condition that triggers switching the image formation mode to the standby mode. An example of a standby condition is when the time during which the image forming apparatus 100 does not form an image exceeds a threshold time. If the standby condition is not satisfied, the CPU 550 proceeds to S810. In S810, the CPU 550 controls the temperature of the fixing device 120 to a target temperature at which image formation can be performed. This target temperature (e.g., 160°C to 180°C) is a temperature equal to or higher than the standby temperature (e.g., 150°C) described above. For example, the CPU 550 selects the duty ratio of the heaters 341 to 346 depending on the size and basis weight of the sheet P, whether the sheet is glossy, etc. Control information indicating the relationship between the size and basis weight of the sheet P, whether the sheet is glossy, and the duty ratio of the heaters 341 to 346 is stored in the ROM area of ​​the memory 560. The CPU 550 determines the duty ratios of the heaters 341-346 by referring to the control information stored in the memory 560. The CPU 550 generates and outputs the control signals 531-536 according to the selected duty ratios. Thereafter, the CPU 550 advances the process to S801. When the standby condition is satisfied in S801, the CPU 550 advances the process to S802.

[0043] In S802, the CPU 550 turns on the heater 341 and turns off the heater 345. This results in the central region being mainly heated. The heater 341 belongs to a first heater group 561 that receives power from a first power supply system 511. The heater 345 belongs to a second heater group 562 that receives power from a second power supply system 512. The first heater group 561 and the second heater group 562 are turned on / off exclusively or alternately.

[0044] In S803, the CPU 550 measures the central temperature M using the thermistor 301. The CPU 550 may convert the detected value output from the thermistor 301 into the central temperature M, which is temperature information, using a table stored in the ROM area of ​​the memory 560.

[0045] In S804, the CPU 550 determines whether the central temperature M exceeds the upper limit temperature (e.g., 155°C). As described above, the upper limit temperature (e.g., 155°C) is set in consideration of the control margin for the standby temperature (e.g., 150°C). The upper limit temperature (e.g., 155°C) is stored in the ROM area of ​​the memory 560. If the central temperature M does not exceed the upper limit temperature, the CPU 550 proceeds to S805. In S805, the CPU 550 determines whether an image formation instruction has been input by the user. If an image formation instruction has been input, the CPU 550 switches the operating mode from the standby mode to the image formation mode and proceeds to S810. On the other hand, if an image formation instruction has not been input in S805, the CPU 550 proceeds to S803. The central temperature M is measured again in S803. A wait process may be provided so that the central temperature M is acquired at predetermined intervals (e.g., 100 milliseconds). If the central temperature M exceeds the upper limit temperature in S804, the CPU 550 advances the process to S806, which corresponds to time T3 in FIG.

[0046] In S806, the CPU 550 turns off the heater 341 and turns on the heater 345. This causes the edge regions to be mainly heated, and the temperature of the central region to decrease. In this manner, the first heater group 561 and the second heater group 562 are turned on / off exclusively or alternately.

[0047] In S807, the CPU 550 measures the end temperature R using the thermistor 302. The CPU 550 may convert the detected value output from the thermistor 302 into the end temperature R, which is temperature information, using a table stored in the ROM area of ​​the memory 560.

[0048] In S808, the CPU 550 determines whether the edge temperature R exceeds an upper limit temperature (e.g., 155°C). If the edge temperature R does not exceed the upper limit temperature, the CPU 550 proceeds to S809. In S809, the CPU 550 determines whether an image formation instruction has been input by the user. If an image formation instruction has been input, the CPU 550 switches the operation mode from the standby mode to the image formation mode, and proceeds to S810. On the other hand, if an image formation instruction has not been input in S809, the CPU 550 proceeds to S807. In S807, the edge temperature R is measured again. A wait process may be provided so that the edge temperature R is acquired at predetermined intervals (e.g., 100 milliseconds). S80 8 If the end temperature R exceeds the upper limit temperature, the CPU 550 advances the process to S802, which corresponds to time T4 in FIG.

[0049] As described above, according to the first embodiment, during the standby period, heaters 341 and 345, which have different power supply systems, are alternately turned on and off. This alternately heats the central region and edge regions of fixing belt 210, and the temperature of fixing belt 210 is maintained at the standby temperature. By alternately turning on heaters 341 and 345 in this way, the lighting cycles of heaters 341 and 345 are each longer than the lighting cycles when heaters 341 and 345 are simultaneously turned on. In other words, flicker during the standby period is improved.

[0050] In the first embodiment, the on / off switching timing of the heater 341 coincides with the off / on switching timing of the heater 345, but this is merely an example. The period in which the heater 341 is on may overlap with the period in which the heater 345 is on. Also, the period in which the heater 341 is off may overlap with the period in which the heater 345 is on.

[0051] In the first embodiment, the heater 341 that mainly heats the central region and the heater 345 that mainly heats the edge region alternately operate during the standby period, but this is merely an example. To reduce flicker, the first heater group 561 connected to the first power supply system 511 and the second heater group 562 connected to the second power supply system 512 may be alternately turned on / off. Here, one or more of the heaters 341 to 343 in the first heater group 561 and one or more of the heaters 344 to 346 in the second heater group 562 may be alternately turned on / off.

[0052] Incidentally, the heat dissipation performance of the edge regions of the heating roller 240 is higher than that of the central region. Therefore, the temperature of the edge regions tends to be lower than that of the central region. Therefore, heater 342, which can heat the central region and edge regions evenly, and heater 344, which consumes less power and mainly heats the edge regions, may be turned on and off alternately.

[0053] The heat dissipation performance of the central region may be improved more than that of the end regions by changing the shape of the heating roller 240. In this case, the heater 342 capable of uniformly heating the central region and the end regions and the heater 346 that mainly heats the central region may be alternately turned on and off.

[0054] <Example 2> In the first embodiment, one heater 341 in the first heater group 561 and one heater 345 in the second heater group 562 are alternately turned on and off. In the second embodiment, in the standby mode, the heater 344 in the second heater group 562 also participates in heating the heating roller 240. In other words, the heater 344 assists the heater 345. The explanation of the first embodiment is used to explain matters common to the first embodiment in the second embodiment.

[0055] [Anti-flicker] 9(A) to 9(D) are diagrams illustrating the duty ratios of heaters 341 to 346 during the standby period in the second embodiment. FIG. 9(A) shows the central temperature M detected by thermistor 301 and the edge temperature R detected by thermistor 302. FIG. 9(B) shows control signals 531, 534, and 535. It is assumed that control signals 532, 533, and 536 are all off. FIG. 9(C) shows the voltage of the first power supply system 511. FIG. 9(D) shows the voltage of the second power supply system 512. In FIGS. 9(A) to 9(D), the horizontal axis represents time.

[0056] The power required by the fixing device 120 during the standby period is less than the power required by the fixing device 120 during the image formation period. Therefore, basically, only the heater 341, which mainly heats the central region, and the heater 345, which mainly heats the edge regions, are turned on during the standby period. In other words, as shown in FIG. 9B, in the second embodiment as well, the heaters 341 and 345 are turned on and off alternately.

[0057] 9(A) shows, as an example, that when the standby temperature is 150° C., the temperature control range during the standby period is from 145° C. to 155° C. Time T5 is the timing when the central temperature M exceeds 155° C. while heater 341 is on and heaters 342 to 346 are off.

[0058] At time T5, CPU 550 detects edge temperature R. If edge temperature R exceeds 145° C., CPU 550 sets the levels of control signals 531 and 535 to turn off heater 341 and turn on heater 345. That is, control signal 531 is switched from High to Low, and control signal 535 is switched from Low to High. As a result, center temperature M starts to decrease and edge temperature R starts to increase.

[0059] Time T6 is the timing when the edge temperature R exceeds 155° C. At time T6, the CPU 550 turns off the heater 345 and turns on the heater 341. That is, the control signal 531 is switched from low to high, and the control signal 535 is switched from high to low. As a result, the edge temperature R starts to decrease, and the center temperature M starts to increase.

[0060] Time T7 is the timing when the central temperature M exceeds 155°C. At time T7, the CPU 550 turns off the heater 341 and turns on the heater 345. Furthermore, at time T7, the CPU 550 detects the edge temperature R. As shown in FIG. 9A, the edge temperature R is below 145°C. In other words, it is necessary to rapidly increase the edge temperature R. Therefore, at time T7, the CPU 550 switches the control signal 534 from low to high to also turn on the heater 344. As shown in FIG. 4B, the heaters 344 and 345 have high heat generation capabilities in the edge regions. This causes the edge temperature R to rise rapidly. Thus, at time T7, the heaters 344 and 345 of the second heater group 562 connected to the second power supply system 512 are simultaneously turned on.

[0061] By repeating this heater control, the CPU 550 can maintain the temperature of the fixing device 120 at the standby temperature (e.g., 150°C). Because the heaters 341 and 345 are alternately turned on and off, the temperature rise and fall slopes become gentler. The edge temperature R is detected when the heater 341 is turned off. The on / off of the heater 344 is determined based on this edge temperature R. This lengthens the on cycle while maintaining the temperature of the fixing device 120 at the standby temperature. As shown in FIG. 9C, the frequency of voltage fluctuations in the first power supply system 511 decreases. As shown in FIG. 9D, the frequency of voltage fluctuations in the second power supply system 512 also decreases. This reduces flickering. Furthermore, the heater 341 is connected to the first power supply system 511, and the heaters 344 and 345 are connected to the second power supply system 512. Therefore, the flicker cycle is longer in the second embodiment as well, compared to when the heaters 341, 344, and 345 are connected to the same power supply system.

[0062] [flowchart] Fig. 10 shows a control method for the fixing device 120 executed by the CPU 550. The steps in Fig. 10 that differ from the steps in Fig. 8 will be described in detail below.

[0063] When the standby condition is satisfied in S801, the CPU 550 advances the process to S1000. In S1000, the CPU 550 turns on the heater 341 and turns off the heaters 344 and 345. This results in the central region being primarily heated. In the second embodiment as well, the first heater group 561 and the second heater group 562 are basically turned on / off exclusively or alternately. Thereafter, the CPU 550 executes S803 to S805. In particular, when the central temperature M exceeds the upper limit temperature in S804, the CPU 550 advances the process to S1001.

[0064] In S1001, the CPU 550 measures the end temperature R using the thermistor 302. A wait process may be provided so that the end temperature R is acquired at predetermined intervals (for example, every 100 milliseconds).

[0065] In S1002, the CPU 550 determines whether the edge temperature R exceeds a lower limit temperature (e.g., 145°C). If the edge temperature R exceeds the lower limit temperature, the CPU 550 proceeds to S1003. This corresponds to time T5. In S1003, the CPU 550 turns off the heaters 341 and 344 and turns on the heater 345. This makes it possible to gradually increase the edge temperature R while decreasing the central temperature M. Thereafter, the CPU 550 proceeds to S807. If the edge temperature R does not exceed the lower limit temperature in S1002, the CPU 550 proceeds to S1004. This corresponds to time T7 in FIG. 9A. In S1004, the CPU 550 turns off the heater 341 and turns on the heaters 344 and 345. This makes it possible to rapidly increase the edge temperature R while decreasing the central temperature M. Thereafter, the CPU 550 advances the process to step S807.

[0066] 8, if the result of S809 is No, the CPU 550 proceeds to S807. In the second embodiment, if the result of S809 is No, the CPU 550 may proceed to S1001. This makes it possible to turn on / off the heater 344 that supplements the heater 345 in accordance with the end temperature R. However, even in the second embodiment, if the result of S809 is No, the CPU 550 may proceed to S807.

[0067] As described above, according to the second embodiment, during the standby period, heater 341 and heaters 344 and 345, which are powered by different power supplies, are alternately turned on and off. This alternately heats the central region and edge regions of fixing belt 210, maintaining the temperature of fixing belt 210 at the standby temperature. In this way, heater 341 and heaters 344 and 345 are alternately turned on. As a result, the lighting cycle of heater 341 and the lighting cycle of heaters 344 and 345 are each longer than the lighting cycle when heaters 341, 344, and 345 are simultaneously turned on. In other words, flicker during the standby period is improved.

[0068] Furthermore, when the central temperature M exceeds the upper limit temperature, the heater 344 is turned on / off according to the edge temperature R. That is, when the edge temperature R is equal to or lower than the lower limit temperature, the heater 344 is turned on. When the edge temperature R exceeds the lower limit temperature, the heater 344 is maintained off. Like the heater 345, the heater 344 is connected to the second power supply system 512 and is a heat source that mainly heats the edge region. The on / off of the heater 344 is basically linked to the on / off of the heater 345. Therefore, the lighting cycle of the second heater group 562 still matches the lighting cycle of the heater 345. That is, even when the auxiliary heater 344 is turned on / off, the flicker is less likely to worsen.

[0069] In the second embodiment, the on / off timing of the heater 341 coincides with the off / on timing of the heaters 344 and 345, but this is merely an example. As explained in the first embodiment, the period during which the heater 341 is on may overlap with the period during which the heaters 344 and 345 are on. Furthermore, the period during which the heater 341 is off may overlap with the period during which the heaters 344 and 345 are off.

[0070] Example 3 In the second embodiment, a case has been described in which multiple heaters in the second heater group 562 (heaters 344 and 345 that mainly heat the end regions) operate during the standby period. However, multiple heaters belonging to the first heater group 561 may operate during the standby period. For example, heaters 341 and 342 that mainly heat the central region of the heating roller 240 may operate during the standby period.

[0071] Fig. 11 shows a control method for the fixing device 120 executed by the CPU 550. Among the steps in Fig. 11, those steps that differ from the steps in Fig. 8 or Fig. 10 will be described in detail below.

[0072] When the standby condition is satisfied in S801, the CPU 550 advances the process to S1101. In S1101, the CPU 550 measures the central temperature M using the thermistor 301. A wait process may be provided so that the central temperature M is acquired every predetermined period (e.g., 100 milliseconds).

[0073] In S1102, the CPU 550 determines whether the central temperature M exceeds a lower limit temperature (e.g., 145° C.). If the central temperature M exceeds the lower limit temperature, the CPU 550 proceeds to S1103. In S1103, the CPU 550 turns on the heater 341 and turns off the heaters 342 and 345. This makes it possible to gradually increase the central temperature M. Thereafter, the CPU 550 proceeds to S803. If the central temperature M does not exceed the lower limit temperature in S1102, the CPU 550 proceeds to S1104. In S1104, the CPU 550 turns on the heaters 341 and 342 and turns off the heater 345. This makes it possible to rapidly increase the central temperature M. Thereafter, the CPU 550 proceeds to S803. Note that if the determination in S805 is No, the CPU 550 may proceed to S1101.

[0074] If the central temperature M exceeds the upper limit temperature in S804, the CPU 550 proceeds to S1105. In S1105, the CPU 550 turns off the heaters 341 and 342 and turns on the heater 345. This makes it possible to increase the end temperature R while decreasing the central temperature M.

[0075] As described above, according to the third embodiment, during the standby period, heaters 341 and 342, which are powered by different power supplies, and heater 345 are alternately turned on and off. Heater 342 is turned on only when assistance from heater 341 is required. This alternately heats the central region and edge regions of fixing belt 210, maintaining the temperature of fixing belt 210 at the standby temperature. Furthermore, the lighting periods of heaters 341 and 342 and heater 345 are each longer than the lighting periods when heaters 341, 342, and 345 are simultaneously turned on. In other words, flicker during the standby period is improved.

[0076] Example 4 Example 4 is a combination of Example 2 and Example 3. That is, during the standby period, the heaters 341 and 342 belonging to the first heater group 561 and the heaters 344 and 345 belonging to the second heater group 562 may be operated.

[0077] Fig. 12 shows a control method for the fixing device 120 executed by the CPU 550. The steps in Fig. 12 that differ from the steps in Fig. 8, Fig. 10 or Fig. 11 will be described in detail below.

[0078] Step S110 in FIG. 11 3 is replaced by step S1201 in FIG. 12, and step S110 in FIG. 4 is replaced by step S1202 in Figure 12. In S1201, CPU 550 turns on heater 341 and turns off heaters 342, 344, and 345. In other words, if center temperature M exceeds the lower limit temperature, fixing belt 210 is heated only by heater 341. On the other hand, in S1202, CPU 550 turns on heaters 341 and 342 and turns off heaters 344 and 345. If center temperature M is equal to or lower than the lower limit temperature, fixing belt 210 is heated by both heaters 341 and 342.

[0079] 12, S1003 and S1004 in FIG. 10 are replaced with S1203 and S1204. In S1203, CPU 550 turns off heaters 341, 342, and 344 and turns on heater 345. In other words, when end temperature R exceeds the lower limit temperature, fixing belt 210 is heated only by heater 345. On the other hand, in S1204, CPU 550 turns off heaters 341 and 342 and turns on heaters 344 and 345. In other words, when end temperature R is equal to or lower than the lower limit temperature, fixing belt 210 is heated by both heaters 344 and 345.

[0080] <Technical ideas derived from examples> [Point 1] As shown in FIG. 5 and other figures, power cord 501 is connected to a first power supply system 511, and power cord 502 is connected to a second power supply system 512. A first heater group 561 has one or more heaters (e.g., heaters 341-343) that receive power from the first power supply system and generate heat. A second heater group 562 has one or more heaters (e.g., heaters 344-346) that receive power from the second power supply system and generate heat. Heat roller 240 and fixing belt 210 function as a heat transfer medium that transfers heat output from the first heater group and the second heater group to the toner image and the sheet. As shown in FIG. 3 and other figures, heat roller 240 and fixing belt 210 are an example of a heat transfer medium that extends in a direction (e.g., the Y direction) that intersects with the conveyance direction of sheet P. A CPU 550 is an example of a control unit that controls the first heater group and the second heater group. The CPU 550 may be realized by a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The CPU 550 controls the temperature of the heat propagation medium to a fixing temperature (e.g., 160°C) during a fixing period (image formation period) in which a toner image is fixed to the sheet P. The CPU 550 controls the temperature of the heat propagation medium to a standby temperature (e.g., 150°C) lower than the fixing temperature during a standby period before the fixing period. During the standby period, the CPU 550 may alternately operate a first heater (e.g., heater 341) included in the first heater group and a second heater (e.g., heater 345) included in the second heater group. This allows the CPU 550 to maintain the temperature of the heat propagation medium at the standby temperature. As shown in FIG. 4A, the heat generation capacity (e.g., 100%) of the center of the first heater in the extending direction of the first heater may be equal to or greater than the heat generation capacity (e.g., 20%) of the end of the first heater. 4(B), the heat generation capacity of the end portion of the second heater in the direction in which the second heater extends may be equal to or greater than the heat generation capacity of the center portion of the second heater. In this way, the first heater and the second heater alternately generate heat, which makes it possible to improve flicker over a long period of time during the standby period of the image forming apparatus 100.Since the heat generation capacity of the first heater and the heat generation capacity of the second heater are set to complement each other, the temperature of each surface area in the extension direction (Y direction) of the heat propagation medium is easily maintained at a generally uniform temperature (e.g., standby temperature ±5°C).

[0081] [Point 2] During the standby period, the first heater and the second heater alternately operate, which may mean that the period during which the first heater generates heat and the period during which the second heater generates heat are longer than the period during which the first heater and the second heater simultaneously generate heat. For example, the period during which the first heater generates heat and the period during which the second heater generates heat may overlap. Alternatively, the period during which the first heater is stopped and the period during which the second heater is stopped may overlap.

[0082] [Point 3] During the standby period, the first heater and the second heater alternately operate, which may mean that the second heater is turned off during a period when the first heater is operating, and the first heater is turned off during a period when the second heater is operating, as illustrated in FIG.

[0083] [Point 4] Thermistor 301 is an example of a first temperature sensor that measures the temperature of the center of the heat propagation medium in the direction in which the heat propagation medium extends. Thermistor 302 is an example of a second temperature sensor that measures the temperature of the end of the heat propagation medium in the direction in which the heat propagation medium extends. CPU 550 may control the first heater group and the second heater group based on the detection result of the first temperature sensor (e.g., center temperature M) and the detection result of the second temperature sensor (e.g., end temperature R).

[0084] [Point 5] As shown in FIG. 8, during the standby period, the center temperature M may exceed an upper limit temperature (e.g., 155°C) that is higher than the standby temperature (e.g., 150°C). In this case, the CPU 550 may stop the first heater and operate the second heater. The temperature of the end of the heat propagation medium (e.g., end temperature R) may also exceed the upper limit temperature. In this case, the CPU 550 may stop the second heater and operate the first heater. This makes it possible to reduce flicker while maintaining the temperature of the fixing device 120 at the standby temperature.

[0085] [Point 6] In the Y direction, the heat dissipation performance of the end portion of the heat propagation medium may be higher than the heat dissipation performance of the center portion of the heat propagation medium. As illustrated in FIG. 4A, in the direction in which a first heater (e.g., heater 342) extends, the heat generation capacity of the center portion of the first heater may be equal to the heat generation capacity of the end portion of the first heater. As illustrated in FIG. 4B, in the direction in which a second heater (e.g., heater 344) extends, the heat generation capacity of the end portion of the second heater may be higher than the heat generation capacity of the center portion of the second heater.

[0086] [Point 7] As described in Example 1, the first heater group may include a third heater (e.g., heater 342) that operates during the fixing period and does not operate during the standby period. As illustrated in Figure 4(A), the heat generating capacity of the end portion of the third heater in the direction in which the third heater extends may be equal to the heat generating capacity of the center of the third heater.

[0087] [Point 8] The first heater group may further include a fourth heater (e.g., heater 343) that operates during the fixing period but does not operate during the standby period. As illustrated in FIG. 4A, the heat generating capacity of the end portion of the fourth heater in the direction in which the fourth heater extends may be higher than the heat generating capacity of the center portion of the fourth heater. This allows the target temperature during the fixing period to be set higher than the standby temperature.

[0088] [Point 9] The second heater group may further include a fifth heater (e.g., heater 344) that operates during the fixing period but does not operate during the standby period. As shown in FIG. 4B, the heat generating capacity of the fifth heater at its ends may be higher than that of its center in the direction in which the fifth heater extends. This allows the target temperature during the fixing period to be set higher than the standby temperature.

[0089] [Point 10] The second heater group may further include a sixth heater (e.g., heater 346) that operates during the fixing period but does not operate during the standby period. As shown in FIG. 4B, the heat generating capacity of the center of the sixth heater may be higher than the heat generating capacity of the ends of the sixth heater in the direction in which the sixth heater extends. This allows the target temperature during the fixing period to be set higher than the standby temperature.

[0090] [Point 11] As described in the second embodiment, the second heater group may further include a seventh heater (e.g., heater 344) that operates during the fixing period and the standby period. As illustrated in FIG. 4B, the heat generating capacity of the seventh heater at its ends may be higher than that of the center of the seventh heater in the direction in which the seventh heater extends. This allows the seventh heater to assist the second heater during the fixing period and the standby period.

[0091] [Point 12] 10 , during the standby period, if the central temperature M of the heat propagation medium exceeds the upper limit temperature and the end temperature R is equal to or lower than the lower limit temperature, the CPU 550 may turn off the first heater and turn on the second and seventh heaters. If the central temperature M exceeds the upper limit temperature and the end temperature R exceeds the lower limit temperature, the CPU 550 may turn off the first and seventh heaters and turn on the second heater. If the end temperature exceeds the upper limit temperature, the CPU 550 may turn off the second and seventh heaters and turn on the first heater.

[0092] [Point 13] As described in the third embodiment, heater 342 is an example of an eighth heater that is provided in the first heater group and operates during the fixing period and the standby period. There are cases where central temperature M does not exceed the upper limit temperature and is equal to or lower than the lower limit temperature (No in S1102). In this case, CPU 550 may turn on the first heater and the eighth heater and turn off the second heater. There are cases where central temperature M does not exceed the upper limit temperature and is higher than the lower limit temperature (Yes in S1102). In this case, CPU 550 may turn on the first heater and turn off the second heater and the eighth heater. Thereafter, when central temperature M exceeds the upper limit temperature, CPU 550 may turn off the first heater and the eighth heater and turn on the second heater.

[0093] [Point 14] As described in the fourth embodiment, heater 344 is an example of a ninth heater that is provided in the second heater group and operates during the fixing period and the standby period. There are cases where central temperature M does not exceed the upper limit temperature and is equal to or lower than the lower limit temperature (No in S1103). In this case, CPU 550 may turn on the first and eighth heaters and turn off the second and ninth heaters. There are cases where central temperature does not exceed the upper limit temperature and is higher than the lower limit temperature (Yes in S1102). In this case, CPU 550 may turn on the first heater and turn off the second, eighth, and ninth heaters. There are cases where edge temperature R exceeds the lower limit temperature when or after central temperature M exceeds the upper limit temperature (Yes in S1002). In this case, CPU 550 may turn off the first, eighth, and ninth heaters and turn on the second heater. When or after the center temperature M exceeds the upper limit temperature, the end temperature R may be equal to or lower than the lower limit temperature (No in S1002). In this case, the CPU 550 may turn off the first heater and the eighth heater and turn on the second heater and the ninth heater.

[0094] [Point 15] As described at the end of Example 1, the heat dissipation performance of the center of the heat propagation medium may be higher than the heat dissipation performance of the end of the heat propagation medium in the Y direction. In this case, the heat generation capacity of the center of the first heater (e.g., heater 342) may be equal to the heat generation capacity of the end of the first heater in the direction in which the first heater extends. In the direction in which the second heater (e.g., heater 346) extends, the heat generation capacity of the center of the second heater may be higher than the heat generation capacity of the end of the second heater.

[0095] [Points 16, 17] The heat transmission medium may have a rotating body (e.g., fixing belt 210) that rotates so as to come into contact with sheet P, and a roller (e.g., heating roller 240) that drives the rotating body or is driven by the rotating body. As illustrated in FIGS. 2 and 3, the first heater group and the second heater group may be provided inside the roller. The rotating body may be an endless belt (e.g., fixing belt 210) that is stretched around the roller. The rotating body may be a cylindrical or columnar roller, etc.

[0096] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0097] 501, 502: power cord, 511, 512: power supply system, 561, 562: heater group, 210: fixing belt, 240: heating roller, 550: CPU, 341 to 346: heater

Claims

1. an image forming means for forming an image on a sheet; A fixing means for fixing the image to the sheet, a first heater that generates heat when a first current is supplied from a first power source, the first heater having a first region capable of generating heat and a second region capable of generating heat at a position different from the first region in a longitudinal direction of the first heater, the first region having a higher heat generating capacity than the second region; a first switch disposed between the first heater and the first power source, the first switch switching whether or not the first current is supplied to the first heater; a second heater that generates heat when a second current is supplied from a second power source different from the first power source, wherein a heat generation distribution characteristic of the second heater in a longitudinal direction of the second heater is different from a heat generation distribution characteristic of the first heater in the longitudinal direction of the first heater, the second heater having a third region capable of generating heat and a fourth region capable of generating heat at a position different from the third region in the longitudinal direction of the second heater, and wherein the heat generation capacity of the third region is lower than that of the fourth region; a third heater that generates heat when a third current is supplied from the first power source; a fourth heater that generates heat when a fourth current is supplied from the second power source; the first region of the first heater overlaps with the third region of the second heater; the second region of the first heater overlaps with the fourth region of the second heater; a fixing unit including a second switch disposed between the second heater and the second power source, the second switch switching whether or not the second current is supplied to the second heater; a control means; The control means In an image forming mode in which the image is formed on the sheet, the first switch and the second switch are controlled so that the temperature of the fixing means is maintained at a fixing temperature for fixing the image on the sheet; an image forming apparatus, characterized in that, in a standby mode in which the image is not formed on the sheet, the third current supplied to the third heater is cut off, the fourth current supplied to the fourth heater is cut off, and the first switch and the second switch are controlled so that the temperature of the fixing means maintains a standby temperature in the standby mode; and the first switch and the second switch are controlled so that a period in which the first current flows to the first heater and a period in which the second current flows to the second heater do not overlap.

2. the first region corresponds to a region different from an end region in the longitudinal direction of the first heater, the second region corresponds to the end region in the longitudinal direction of the first heater, the third region corresponds to a region different from an end region in the longitudinal direction of the second heater, the fourth region corresponds to the end region in the longitudinal direction of the second heater; 2. The image forming apparatus according to claim 1, wherein:

3. a first temperature sensor for measuring a temperature at a first position of the fixing means; a second temperature sensor for measuring the temperature of the fixing means at a second position different from the first position; 3. The image forming apparatus according to claim 1, wherein the control means is configured to control the first switch and the second switch so that, in the standby mode, the detected temperatures of the first temperature sensor and the second temperature sensor maintain the standby temperature.

4. 4. The image forming apparatus according to claim 1, wherein the standby temperature has a temperature range from an upper limit temperature to a lower limit temperature.

5. the first heater includes a halogen heater, The second heater includes a halogen heater.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. 6. The image forming apparatus according to claim 1, wherein the standby temperature is lower than the fixing temperature.

7. an image forming means for forming an image on a sheet; A fixing means for fixing the image to the sheet, a first heater that generates heat when a first current is supplied from a first power source, the first heater having a first region capable of generating heat and a second region capable of generating heat at a position different from the first region in a longitudinal direction of the first heater, the first region having a higher heat generating capacity than the second region; a first switch disposed between the first heater and the first power source, the first switch switching whether or not the first current is supplied to the first heater; a second heater that generates heat when a second current is supplied from a second power source different from the first power source, wherein a heat generation distribution characteristic of the second heater in a longitudinal direction of the second heater is different from a heat generation distribution characteristic of the first heater in the longitudinal direction of the first heater, the second heater has a third region capable of generating heat and a fourth region capable of generating heat at a position different from the third region in the longitudinal direction of the second heater, and wherein the heat generation capacity of the third region is lower than that of the fourth region; a third heater that generates heat when a third current is supplied from the first power source; a fourth heater that generates heat when a fourth current is supplied from the second power source; wherein the first region of the first heater overlaps with the third region of the second heater in a longitudinal direction of the first heater; the second region of the first heater overlaps with the fourth region of the second heater in a longitudinal direction of the first heater, a fixing unit including a second switch disposed between the second heater and the second power source, the second switch switching whether or not the second current is supplied to the second heater; a control means; The control means In an image forming mode in which the image is formed on the sheet, the first switch and the second switch are controlled so that the temperature of the fixing means is maintained at a fixing temperature provided as a target temperature for fixing the image on the sheet; an image forming apparatus, characterized in that, in a standby mode in which the image is not formed on the sheet, the third current supplied to the third heater is cut off, the fourth current supplied to the fourth heater is cut off, and the first switch and the second switch are controlled so that the temperature of the fixing means maintains a standby temperature in the standby mode; and the timing at which the first current starts to be supplied from the first power source and the timing at which the second current starts to be supplied from the second power source are made different, thereby controlling the first switch and the second switch so that the rate of increase in the temperature of the fixing means is slower than when the timing at which the first current starts to be supplied from the first power source and the timing at which the second current starts to be supplied from the second power source are the same.

8. the first region corresponds to a region different from an end region in the longitudinal direction of the first heater, the second region corresponds to the end region in the longitudinal direction of the first heater, the third region corresponds to a region different from an end region in the longitudinal direction of the second heater, the fourth region corresponds to the end region in the longitudinal direction of the second heater; 8. The image forming apparatus according to claim 7,

9. a first temperature sensor for measuring a temperature at a first position of the fixing means; a second temperature sensor for measuring the temperature of the fixing means at a second position different from the first position; 9. The image forming apparatus according to claim 7, wherein the control means is configured to control the first switch and the second switch so that, in the standby mode, the detected temperatures of the first temperature sensor and the second temperature sensor maintain the standby temperature.

10. 10. The image forming apparatus according to claim 7, wherein the standby temperature has a temperature range from an upper limit temperature to a lower limit temperature.

11. the first heater includes a halogen heater, The second heater includes a halogen heater.

11. The image forming apparatus according to claim 7, wherein the image forming apparatus is a recording medium.

12. 12. The image forming apparatus according to claim 7, wherein the standby temperature is lower than the fixing temperature.

Images