Like a heating device

Abstract

To solve the problem in which: even if two or more heat generating blocks are commonly supplied with power, heating values may be different.SOLUTION: An image heating device comprises: a heater in which a plurality of heat generating blocks including a first heat generating block and a second heat generating block different in a resistance value from the first heat generating block is arranged side by side in a direction orthogonal to a conveyance direction of a recording material; a first temperature detection member that detects a temperature of the first heat generating block; a second temperature detection member that detects a temperature of the second heat generating block; and a control unit. The control unit controls power supplied to a common power supply path to which the first heat generating block and the second heat generating block are electrically connected according to a temperature detected by the first temperature detection member or the second temperature detection member, and uses the temperature detection member having a higher detected temperature in a start-up mode and the temperature detection member having a lower detected temperature in a paper feed mode to control the power supplied to the common power supply path.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an image heating device, such as a fixing device, mounted in an image forming apparatus of an electrophotographic recording system, such as a copying machine or a printer. [Background technology]

[0002] As an image heating device provided in an image forming apparatus using an electrophotographic method, an electrostatic recording method, or the like, there is a device having a fixing film, a heater contacting the inner surface of the fixing film, and a roller forming a nip portion together with the heater via the fixing film. In an image forming apparatus equipped with this image heating device, when an image is continuously formed on a recording material having a size narrower than the maximum paper-passable width in a direction perpendicular to the conveying direction of the recording material (hereinafter referred to as the longitudinal direction), a so-called non-paper-passing portion temperature rise occurs. That is, it is a phenomenon in which the temperature of each part in the area (hereinafter referred to as the non-paper-passing portion) where the recording material does not pass in the longitudinal direction of the nip portion gradually rises. As an image heating device, it is necessary to prevent the temperature of the non-paper-passing portion from exceeding the heat resistance temperature of each member in the device. For this reason, a method of suppressing the temperature rise of the non-paper-passing portion by lowering the throughput of continuous printing (the number of sheets that can be printed per minute) (hereinafter referred to as throughput down) is often used.

[0003] In response to this, a method proposed in Patent Document 1 can be cited as one method for suppressing the temperature rise in the non-paper passing portion without reducing the throughput as much as possible. The method in Patent Document 1 divides a heat generating block consisting of a set of a conductor and a heat generating element at a position corresponding to the size of the recording material in the longitudinal direction of the heater, and controls the power supplied to each divided heat generating block independently. The temperature rise in the non-paper passing portion can be suppressed by not supplying power to the heat generating block corresponding to the non-paper passing portion in the longitudinal direction of the heater except when necessary. In an image heating device configured in this way, two or more heat generating blocks are electrically connected to a common power supply path, and the power supplied to the two or more heat generating blocks may be commonly controlled. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2014-59508 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even if two or more heat generating blocks are commonly supplied with power, the heat generation amounts may differ. In this case, when commonly controlling the power supply to two or more heat generating blocks, it is necessary to control the supply power in consideration of the heat generation amount of each heat generating block. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] An image heating device that heats an image formed on a recording material, a heater in which a plurality of heat generating blocks, including a first heat generating block and a second heat generating block having a resistance value different from that of the first heat generating block, are arranged in a direction perpendicular to a conveying direction of a recording material; a first temperature detection member that is provided in an area overlapping the first heat generating block when the heater is viewed in a thickness direction of the heater and detects a temperature of the first heat generating block; a second temperature detection member that is provided in an area overlapping the second heat generating block when the heater is viewed in a thickness direction of the heater and detects a temperature of the second heat generating block; A control unit that controls the supply of power to the plurality of heat generating blocks; Equipped with the first heat generating block and the second heat generating block are electrically connected to a common power supply path; the control unit controls the power supplied to the common power supply path in response to a first detected temperature detected by the first temperature detection member or a second detected temperature detected by the second temperature detection member; One of the first detected temperature and the second detected temperature is The control target temperature during the start-up period The period until the first temperature is reached is called a first period, and the first detection temperature and the second detection temperature are called a first detection temperature. The one of the After the temperature reaches the first temperature, the period during which the recording material is heated by the heater is defined as a second period. the control unit uses the selected first temperature detection member to control the power supplied to the common power supply path during the first period, and uses the selected second temperature detection member to control the power supplied to the common power supply path during the second period; the first temperature detecting member has a higher detection temperature than the second temperature detecting member; During the second period, the first detected temperature and the second detected temperature are lower than the first temperature. The temperature is set so that the image formed on the recording material does not have a heating defect. The temperature is characterized by being within the range of the first temperature and the second temperature.

[0008] In order to solve the above-mentioned problems, the image forming apparatus of the present invention comprises: an image forming section for forming an image on a recording material; a fixing section for fixing the image formed on the recording material to the recording material; In an image forming apparatus having The fixing unit is the image heating device. Effect of the Invention

[0009] As described above, according to the present invention, when the power supply to two or more heat generating blocks is controlled in common, the supply power can be controlled in consideration of the heat generation amount of each heat generating block. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus 100 according to a first embodiment of the present invention; [Diagram 2] 1 is a schematic diagram of an image heating apparatus according to a first embodiment of the present invention; [Diagram 3] FIG. 1 is a diagram showing the configuration of a heater 300 according to a first embodiment. [Figure 4] A control circuit diagram of a heater 300 according to the first embodiment [Diagram 5] FIG. 1 is a diagram showing the relationship between the heating zone HZ and the fixing film 202 according to the first embodiment. [Figure 6] Temperature transition when heater control is performed using the reference thermistor as the main thermistor TM5 without considering the variation in heat generation amount in Example 1 [Figure 7] Temperature transition when heater control is performed using the reference thermistor as the main thermistor TM3 without considering the variation in heat generation amount in Example 1 [Figure 8] 1 is a flowchart of a process executed by a control unit in heater control according to the first embodiment. [Figure 9] Temperature transition when heater control according to the first embodiment is executed [Figure 10] 10 is a flowchart of a process executed by a control unit in heater control according to a modification of the first embodiment. [Figure 11] Temperature transition when heater control according to the modification of the first embodiment is executed [Figure 12] 11 is a flowchart of a process executed by a control unit in heater control according to a second embodiment. [Figure 13] Temperature transition when heater control according to the second embodiment is executed [Figure 14] 11 is a flowchart of a process executed by a control unit in heater control according to a third embodiment. [Figure 15] Temperature transition when heater control according to the third embodiment is executed [Figure 16] Temperature transition when heater control according to the fourth embodiment is executed DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention of the claims, and all of the combinations of features described in the embodiments are not necessarily essential to the solution of the present invention. EXAMPLES

[0012] 1. Configuration of image forming device FIG. 1 is a schematic diagram of an image forming apparatus 100 in this embodiment. The image forming apparatus 100 is, as an example, an electrophotographic full-color printer that employs an intermediate transfer method. The image forming apparatus 100 has four image forming stations that form images of the respective colors of yellow, magenta, cyan, and black. These four image forming stations are arranged in a row at regular intervals. In the following description, the English letters Y, M, C, and K at the end of the reference symbols indicate that the corresponding members are related to the formation of toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In the following description, when it is not necessary to distinguish between colors, the reference symbols without the English letters Y, M, C, and K at the end are used.

[0013] The image forming apparatus 100 includes a video controller 120 and an engine controller 113. The video controller 120, as an acquisition unit that acquires information on an image to be formed on a recording material, receives and processes image information and a print instruction transmitted from an external device such as a personal computer. The engine controller 113 is connected to the video controller 120, and controls each unit constituting the image forming apparatus 100 according to an instruction from the video controller 120. When the video controller 120 receives a print instruction from an external device, it transmits an instruction to start image formation (hereinafter also referred to as a print start command) to the engine controller 113. When the print start command is transmitted from the video controller 120, power supply to the image heating device 200 and driving of the exposure scanner unit 11 are started, and the recording material P is fed one sheet at a time from the paper feed cassette 15A by the pickup roller 14 and the paper feed rollers 17 and 18. In order to synchronize the toner image formation operation on the intermediate transfer belt 24 described below with the transport operation of the recording material P, the recording material P is clamped between a transport (registration) roller 19a and a transport (registration) opposing roller 19b, and transport is temporarily stopped.

[0014] Next, the image forming operation on the intermediate transfer belt 24 (endless belt) will be described. The photosensitive drum 1 has an organic photoconductive layer on a base on the drum, and is rotated and driven at a predetermined process speed by a driving device (not shown). The process speed here corresponds to the peripheral speed (surface moving speed) of the photosensitive drum 1. The charging roller 2 uniformly charges the photosensitive drum 1 to a predetermined potential. The exposure scanner unit 11 includes a reflecting mirror and a laser diode (light emitting element), and irradiates the surface of the photosensitive drum 1 with laser light corresponding to image information, thereby exposing the surface of the photosensitive drum 1. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1. The developing unit 8 develops the electrostatic latent image into a toner image by attaching toner to the electrostatic latent image formed on the surface of the photosensitive drum 1 by the developing roller 5. The primary transfer roller 4 performs primary transfer of the image formed on the photosensitive drum 1 to the intermediate transfer belt 24. The intermediate transfer belt 24 is also called a rotating body. The intermediate transfer belt 24 is driven by a drive roller 26 and driven rollers 13 and 23. The drive roller in this embodiment may be any of the rollers 26, 13, and 23. The toner remaining on the photosensitive drum 1 after the primary transfer is removed and collected from the photosensitive drum 1 by a drum cleaner 16 installed in contact with the photosensitive drum. The drum cleaner 16 is composed of a cleaner blade 161 and a toner collection container 162. The components from the photosensitive drum 1 to the drum cleaner 16 related to the formation of a toner image on the intermediate transfer belt 24 described above are also referred to as an image forming unit, and the operation performed by the image forming unit is also referred to as an image forming operation.

[0015] The toner image primarily transferred onto the intermediate transfer belt 24 is conveyed to a secondary transfer nip portion formed by a secondary transfer roller 25 and a drive roller 26. At the same time, the recording material P, which is sandwiched between the conveying roller pair 19a and 19b and whose conveyance has been temporarily stopped, is also conveyed to the secondary transfer nip portion, and the toner image primarily transferred onto the intermediate transfer belt 24 is secondarily transferred onto the recording material P by a secondary transfer bias applied to the secondary transfer roller 25. Thereafter, the recording material P is subjected to heat and pressure by a fixing device (image heating device) 200 as a fixing section (image heating section), and the toner image secondarily transferred onto the recording material P is thermally fixed onto the recording material P. Note that power is supplied to the image heating device 200 by a control circuit 400 (control unit) connected to a commercial AC power source 401. The recording material P on which the toner image has been fixed is discharged to a paper discharge tray 31 by discharge rollers 20a and 20b, and the image forming operation onto the recording material P is completed. The belt cleaner 28 cleans the toner remaining on the intermediate transfer belt 24 after the secondary transfer with a cleaner blade 281. The toner collected here is stored in a cleaner container 282 as waste toner.

[0016] In this embodiment, an image forming apparatus is used in which the maximum paper passing width in the direction perpendicular to the conveying direction of the recording material P is 216 mm, and it is possible to print on recording materials of LETTER size (216 mm×279 mm).

[0017] 2. Image heating device configuration 2 is a schematic configuration diagram of image heating device 200 in this embodiment. Image heating device 200 has fixing film 202 as an endless belt, heater 300 (heating means) in contact with the inner surface of fixing film 202, pressure roller 208 in contact with the outer circumferential surface of fixing film 202 to form fixing nip portion N, and metal stay 204.

[0018] The fixing film 202 is a cylindrically formed multi-layer heat-resistant film, with a base layer made of heat-resistant resin such as polyimide or metal such as stainless steel. The surface of the fixing film 202 is coated with a heat-resistant resin with excellent releasability such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) to form a release layer, in order to prevent toner adhesion and ensure separability from the recording material P. Furthermore, to improve image quality, a heat-resistant rubber such as silicone rubber may be formed as an elastic layer between the base layer and the release layer.

[0019] The pressure roller 208 has a core metal 209 made of iron, aluminum, or the like, and an elastic layer 210 made of silicone rubber, etc. The pressure roller 208 may have a release layer formed on its surface, similar to the fixing film 202.

[0020] The heater 300 is held by a heater holding member 201 made of heat-resistant resin, and heats the fixing nip portion N by a heating element provided on a ceramic substrate 305, thereby heating the fixing film 202. The heater 300 will be described in detail later. The heater holding member 201 also has a guide function for guiding the rotation of the fixing film 202. The heater 300 is provided with an electrode E on the opposite side (back side) of the side that contacts the inner surface of the fixing film 202, and power is supplied to the electrode E through an electrical contact C. Here, an electrode E4 is shown as an example of the electrode E, and an electrical contact C4 is shown as an example of the electrical contact C. The metal stay 204 urges the heater holding member 201 toward the pressure roller 208 by receiving a pressure force from an urging member (not shown). In addition, a safety element 212 such as a thermoswitch or a temperature fuse that is activated by abnormal heat generation of the heater 300 to cut off the power supplied to the heater 300 is arranged facing the back side of the heater 300.

[0021] The pressure roller 208 receives power from the motor 30 and rotates in the direction of the arrow R1. As the pressure roller 208 rotates, the fixing film 202 rotates in the direction of the arrow R2. The unfixed toner image on the recording material is fixed by applying heat from the fixing film 202 while nipping and conveying the recording material P in the fixing nip N.

[0022] 3. Heater configuration Fig. 3 shows a configuration diagram of the heater 300 in this embodiment. Fig. 3(A) is a cross-sectional view of the heater 300, and Fig. 3(B) is a plan view for explaining each layer of the heater 300. Fig. 3(B) shows the recording material P in the image forming apparatus 100 of this embodiment. The transport reference in this embodiment is the center reference, and the recording material P is transported so that its center line in a direction perpendicular to the transport direction is aligned with the transport reference position X. Fig. 3(A) is also a cross-sectional view of the heater 300 at the transport reference position X.

[0023] The heater 300 is disposed in the internal space of the fixing film 202. The heater 300 is also composed of a ceramic substrate 305, a back surface layer 1 provided on the substrate 305, a back surface layer 2 covering the back surface layer 1, a sliding surface layer 1 provided on the surface of the substrate 305 opposite to the back surface layer 1, and a sliding surface layer 2 covering the sliding surface layer 1.

[0024] The back surface layer 1 has a first conductor 301 (301a, 301b) provided along the longitudinal direction of the heater 300. The first conductor 301 is separated into a first conductor 301a and a first conductor 301b, and the first conductor 301b is disposed downstream of the first conductor 301a on the substrate in the conveying direction of the recording material P. The back surface layer 1 also has second conductors 303 (303-1 to 303-7) provided in parallel to the first conductor 301a and the first conductor 301b. The second conductor 303 is provided along the longitudinal direction of the heater 300 between the first conductor 301a and the first conductor 301b. Furthermore, the back surface layer 1 has heating elements 302a (302a-1 to 302a-7) and heating elements 302b (302b-1 to 302b-7) which are heating resistors that generate heat when electricity is applied. The heating element 302a is provided between the first conductor 301a and the second conductor 303, and generates heat when power is supplied through the first conductor 301a and the second conductor 303. The heating element 302b is provided between the first conductor 301b and the second conductor 303, and generates heat when power is supplied through the first conductor 301b and the second conductor 303.

[0025] A heat generating portion composed of the first conductor 301, the second conductor 303, the heating element 302a, and the heating element 302b is divided into seven heat generating blocks (HB1 to HB7) in the longitudinal direction of the heater 300. That is, the heating element 302a is divided into seven regions, 302a-1 to 302a-7, in the longitudinal direction of the heater 300. The heating element 302b is divided into seven regions, 302b-1 to 302b-7, in the longitudinal direction of the heater 300. Furthermore, the conductor 303 is divided into seven regions, 303-1 to 303-7, in accordance with the division positions of the heating elements 302a and 302b. The seven heat generating blocks (HB1 to HB7) have their respective heat values ​​individually controlled by individually controlling the amount of current flowing to the heating resistors in each block.

[0026] The heat generating range in this embodiment is the range from the left end of the heat generating block HB1 to the right end of the heat generating block HB7, and the range heated by this heat generating range is divided into seven heating regions (HZ1 to HZ7). Of the seven heating regions, the total length from the left end of the heating region HZ1 to the right end of the heating region HZ7 is 216 mm, which corresponds to the width of a LETTER size. The length from the left end of the heating region HZ2 to the right end of the heating region HZ6 is 210 mm, which corresponds to the width of an A4 size. The length from the left end of the heating region HZ3 to the right end of the heating region HZ5 is 182 mm, which corresponds to the width of a B5 size. The length from the left end of the heating region HZ4 to the right end is 105 mm, which corresponds to the width of an A6 size.

[0027] The back surface layer 1 also has electrodes E (E1 to E7, and E8-1 and E8-2). The electrodes E1 to E7 are provided in the areas of the conductors 303-1 to 303-7, respectively, and are electrodes for supplying power to the heat generating blocks HB1 to HB7 via the conductors 303-1 to 303-7. The electrodes E8-1 and E8-2 are electrodes for supplying power to the heat generating blocks HB1 to HB7 via the first conductor 301a and the first conductor 301b at the longitudinal end portions of the heater 300. In this embodiment, the electrodes E8-1 and E8-2 are provided at both longitudinal ends of the heater 300, but, for example, a configuration in which only the electrode E8-1 is provided on one side (i.e., a configuration in which the electrode E8-2 is not provided) may be used. Furthermore, although power is supplied to the conductors 301a and 301b through a common electrode, individual electrodes may be provided for the conductors 301a and 301b, and power may be supplied to each of them.

[0028] The back surface layer 2 is composed of an insulating surface protection layer 307 (glass in this embodiment), and covers the first conductor 301, the second conductor 303, and the heating elements 302a and 302b. The surface protection layer 307 is formed except for the location of the electrode E, and is configured so that an electrical contact C can be connected to the electrode E from the back surface layer 2 side of the heater.

[0029] The slide surface layer 1 is provided on the surface of the substrate 305 opposite to the surface on which the back surface layer 1 is provided. Main thermistors (control temperature detection means) TM1 to TM5, TM7 and sub-thermistors TS2 to TS6 are provided as detection elements for detecting the temperatures of the heat generating blocks HB1 to HB7. The roles of the main thermistor and sub-thermistor will be described later. Thermistor TH is made of a material having PTC characteristics or NTC characteristics (NTC characteristics in this embodiment), and by detecting its resistance value, the temperatures of all the heat generating blocks can be detected. Note that, from the standpoint of placement space and cost, in this embodiment, a main thermistor is not provided in the heating region HZ6.

[0030] The slide surface layer 1 also has conductors ETM (ETM1 to ETM5, ETM7) for passing a current through the main thermistor TM and detecting its resistance value. The slide surface layer 1 also has conductors ETS (ETS2 to ETS6) for passing a current through the sub-thermistor TS and detecting its resistance value. The conductors ETM1 to ETM5, ETM7 are connected to the main thermistors TM1 to TM5, TM7, respectively, and the conductors ETS2 to ETS6 are connected to the sub-thermistors TS2 to TS6, respectively. The conductor EG1 is connected to the six main thermistors TM1 to TM5, TM7 and forms a common conductive path. The conductor EG2 is connected to the six sub-thermistors TS2, TS3, TS4L, TS4R, TS5, TS6 and forms a common conductive path. The conductors ETM, ETS and EG are each formed along the longitudinal end of the heater 300, and are connected to a control circuit 400 (described later) via electrical contacts (not shown) at the longitudinal end of the heater.

[0031] The sliding surface layer 2 is composed of a surface protection layer 308 (glass in this embodiment) having sliding properties and insulating properties. The surface protection layer 308 covers the main thermistor TM, the sub thermistor TS, the conductor ETM, the conductor ETS, and the conductor EG, and ensures sliding properties with the inner surface of the fixing film 202. The surface protection layer 308 is formed except for both longitudinal ends of the heater 300 in order to provide electrical contacts with the conductors ETM, ETS, and EG.

[0032] Next, a method of connecting the electrical contacts C to each electrode E will be described. The heater holding member 201 has through holes at positions corresponding to the electrodes E (E1 to E7, and E8-1, E8-2). At each through hole position, the electrical contacts C (C1 to C7, and C8-1, C8-2) are electrically connected to the electrodes E (E1 to E7, and E8-1, E8-2) by a spring or welding or other method. The electrical contacts C are connected to a control circuit 400 of the heater 300, which will be described later, via a conductive material (not shown) provided between the metal stay 204 and the heater holding member 201.

[0033] 4. Heater control circuit configuration FIG. 4 is a circuit diagram of the control circuit 400 of the heater 300 in this embodiment. A commercial AC power source 401 is connected to the image forming apparatus 100 in this embodiment. The power control of the heater 300 is performed by turning on / off the triacs (power supply means) 412-414. The triacs 412-414 operate according to the FUSER2-FUSER4 signals from the CPU 420, respectively. The driving circuits of the triacs 412-414 are omitted. The control circuit 400 of the heater 300 has a circuit configuration that allows the seven heat generating blocks HB1-HB7 to be independently controlled by the three triacs 412-414. By selectively controlling the triacs 412-414, the current supply to the multiple heat generating elements can be selectively controlled, and the multiple heating regions divided in the longitudinal direction can be selectively heated individually. The triac 412 controls the current supply to the heat generating blocks HB1, HB2, HB6, and HB7. The group of heat generating blocks HB1, HB2, HB6, and HB7 to which triac 412 controls the energization is also referred to as drive D1. Triac 413 controls the energization of heat generating blocks HB3 and HB5. The group of heat generating blocks HB3 and HB5 to which triac 413 controls the energization is referred to as drive D2. Triac 414 controls the energization of heat generating block HB4. The group of heat generating block HB3 to which triac 414 controls the energization is also referred to as drive D3. Drives D1 and D2 are in the same drive group, each driving two or more heat generating blocks with one triac.

[0034] Zero cross detection unit 430 is a circuit that detects zero cross of AC power supply 401, and outputs a ZEROX signal to CPU 420. The ZEROX signal is used for detecting the timing of phase control and wave number control of triacs 412-414, and the like.

[0035] The relay 440, which serves as power cut-off means, cuts off power to the heater 300 when the heater 300 overheats due to a malfunction or the like and any of the main thermistors TM1-TM7 and sub thermistors TS2-THS6 detects Ter [°C], which is an overheating threshold value. Ter [°C] is a temperature with a predetermined margin with respect to the temperature at which the heater cracks due to thermal stress when the heater overheats, and is set to Ter=300°C in this embodiment.

[0036] The internal processing of the CPU420 controls the target temperature TGT i Based on (i=1 to 3) and the temperature detected by the main thermistor, the power to be supplied is calculated, for example, by PI control (proportional integral control). Furthermore, the power to be supplied is converted into a control level (duty ratio) of the phase angle (phase control) and wave number (wave number control) corresponding to the power, and the triacs 412 to 414 are controlled according to the control conditions.

[0037] Specifically, drive D1 performs control based on the control target temperature TGT1 and the temperature detected by one of the main thermistors TM1, TM2, and TM7. Drive D2 performs control based on the control target temperature TGT2 and the temperature detected by one of the main thermistors TM3 and TM5. Drive D3 performs control based on the control target temperature TGT3 and the temperature detected by the main thermistor TM4.

[0038] If the control target temperatures TGT1 to TGT3 become too high, there is a possibility that the relay 440 will cut off the power supply due to overheating, so an upper limit target temperature Tlim lower than the overheating threshold Ter is set. In this embodiment, the upper limit target temperature Tlim is set to 280°C, which is a margin of 20°C from the overheating threshold Ter (=300°C).

[0039] In this embodiment, the sub-thermistors TS2 to TS6 are not used to control the power supply to each drive. These thermistors are used to detect the above-mentioned overheating and non-paper passing area temperature rise. Non-paper passing area temperature rise is a phenomenon in which the temperature of the heat generating block corresponding to the non-paper passing area of ​​the heating area rises when the position of the end in the direction perpendicular to the conveying direction of the recording material P does not match the dividing position of the heating areas HZ1 to HZ7.

[0040] 5. Heating area and fixing film 5 is a diagram showing the positional relationship in the longitudinal direction of the heating regions HZ1 to HZ7 in this embodiment and the fixing film 202. The regions of the fixing film 202 corresponding to the heating regions HZ1 to HZ7 are also referred to as TF1 to TF7, respectively.

[0041] 6.Heater control method When starting up the image heating device 400, it is desirable to raise the temperature of the fixing film 202 within the range of the fixing temperature margin as quickly as possible. On the other hand, when passing the recording material P through the fixing nip N, it is desirable to keep the temperature of the fixing film 202 within the range of the fixing temperature margin. For this reason, the control unit may control the temperature of the fixing film 202 differently in the start-up mode and the paper passing mode. At this time, the start-up mode is a control mode in a period from when the supply of power to the heat generating block HB is started until the detected temperature of any of the main thermistors TM in the same drive group reaches a first temperature. The start-up mode is a preparation period for heating the recording material with a heater, and this period is also referred to as a first period. The first temperature at this time will be described later. The paper passing mode is a control mode after the detected temperature of any of the main thermistors TM in the same drive group reaches the first temperature. In the paper passing mode, there is a period in which the recording material is heated by the heater. This period is also referred to as a second period. The fixing temperature margin will be described later.

[0042] In this embodiment, the drive D2, in which the energization is controlled by controlling the triac 413, will be described as an example of a common power supply path controlled by the control circuit 400. In the drive D2 in this embodiment, the heat generating block HB5 and the heat generating block HB3 have a variation in resistance value, and the resistance value of the heat generating block HB5 is smaller than that of the heat generating block HB3. At this time, the heat generation amount of the heat generating block HB5 is larger than that of the heat generating block HB3. In this state, when the power supply to the heat generating block HB5 and the heat generating block HB3 is commonly controlled without considering the variation in the resistance value of the heat generating block, the case of temperature control based only on the main thermistor TM5 will be described using FIG. 6. In addition, when performing the same control, the case of temperature control based only on the main thermistor TM3 will be described using FIG. 7. The heat generating block HB5 is also called the first heat generating block, and the heat generating block HB3 is also called the second heat generating block. In addition, the main thermistor TM5 is also referred to as the first temperature detection member, the main thermistor TM3 is also referred to as the second temperature detection member, the temperature detected by the first temperature detection member is also referred to as the first detected temperature, and the temperature detected by the second temperature detection member is also referred to as the second detected temperature.

[0043] Fig. 6 shows the temperature transition when the heater control of this embodiment is performed in the drive D2. Fig. 6(A) shows the transition of the temperature detected by the main thermistor TM3 (dashed line) and the main thermistor TM5 (solid line) of the drive D2. Of the main thermistors TM3 and TM5, the thermistor TM5 is shown in a thick line as a reference for controlling the power supplied to the drive D2, and the control target temperature TGT2 of the drive D2 is shown in a thick dashed line. Fig. 6(B) shows the temperature transition of the regions TF3 and TF5 of the fixing film 202 corresponding to the heating regions HZ3 and HZ5.

[0044] 6B is a temperature range of the fixing film 202, with a lower limit temperature Tbu and an upper limit temperature Tho. If the temperature of the fixing film 202 is set to the lower limit temperature Tbu or lower, a cold offset occurs in which a part of the toner image does not adhere to the recording material and is missing due to poor fixability of the toner on the recording material P. If the temperature of the fixing film 202 is set to the upper limit temperature Tho or higher, a hot offset occurs in which the toner on the recording material P is excessively heated and adheres to the fixing film 202.

[0045] In FIG. 6A, Tunder is the lower limit threshold temperature, which is set so that the temperature of the fixing film 202 does not fall below the lower limit temperature Tbu when the recording material P passes through the fixing nip N. In other words, it is the temperature set so that cold offset does not occur in the heating area. Ter is the overheating threshold. Tlim is the upper limit target temperature, which is set to a temperature lower than the overheating threshold Ter so that the power supply is not cut off due to the overheating of the heat generating block. Tlim is also set so that the temperature of the fixing film 202 does not exceed the upper limit temperature Tho when the recording material P passes through the fixing nip N. Thus, in this embodiment, the purpose is to execute heater control so that the detected temperature by the main thermistors TM3 and TM5 falls within the range between the lower limit threshold temperature Tunder and the overheating threshold Ter. In this embodiment, when the heater is controlled so that neither the detected temperature by Tmax nor the detected temperature by Tmin falls below the temperature of Tunder, Ttgt, which is lower than Tlim and higher than Tunder, is set as the target temperature. In this embodiment, the upper limit target temperature Tlim is also referred to as the first temperature, the lower limit threshold temperature Tunder is also referred to as the second temperature, and the target temperature Ttgt is also referred to as the third temperature. By executing this heater control, the temperatures of the corresponding areas TF3 and TF5 of the fixing film 202 can be kept within the fixing temperature margin.

[0046] <When controlling temperature based only on main thermistor TM5> First, the case where temperature control is performed based only on the main thermistor TM5 without considering the variation in the resistance value of the heat generating block will be described using the temperature transition of the main thermistor shown in Fig. 6(A). In the start-up mode, control is performed to raise the temperature detected by TM5 to the upper limit target temperature Tlim. By controlling the temperature detected by TM5 to the control target temperature Tlim, it is possible to prevent it from exceeding the overheating threshold Ter.

[0047] Thereafter, when the temperature detected by TM5 reaches Tlim, the mode transitions to the paper passing mode. In the paper passing mode, the thermistor used for control remains TM5, and the control target temperature TGT2 of the drive D2 is set to the target temperature Ttgt after switching, and temperature control is performed.

[0048] 6B, the temperature transition of the fixing film will be described. In the paper passing mode, by controlling the temperature detected by TM5 with Ttgt, the temperature detected by TM3 falls below Tunder, and the temperature of the region TF3 of the fixing film falls below Tbu.

[0049] Therefore, if heater control is performed using only the main thermistor TM5 as the reference for temperature control, the temperatures of the areas TF3 and TF5 of the fixing film in the paper passing mode cannot be kept within the fixing temperature margin.

[0050] <When controlling temperature based only on main thermistor TM3> Next, a case where only the main thermistor TM3 is used as the reference for temperature control without considering the variation in the resistance value of the heat generating block will be described using the temperature transition of the main thermistor shown in Fig. 7(A). In the start-up mode, control is performed to raise the temperature detected by TM3 to the upper limit target temperature Tlim. At this time, the temperature detected by TM5 exceeds Ter, and the power supply to the heater is cut off due to the excessive temperature rise.

[0051] 7B, the temperature transition of the fixing film will be described. Because the power is cut off before the printer enters the paper passing mode, it becomes impossible to detect the temperatures of the heat generating blocks HB3 and HB5 corresponding to the fixing film areas TF3 and TF5 to determine whether the temperatures of the fixing film areas TF3 and TF5 fall within the fixing temperature margin.

[0052] Therefore, if heater control is performed using only the main thermistor TM3 as a reference for temperature control, the image heating operation on the recording material P itself becomes impossible.

[0053] As described above, when there is variation in the resistance value of the drive D2, if only the main thermistor TM5 or only the main thermistor TM3 is used as the reference for temperature control, the temperatures of the fixing film regions TF3 and TF5 cannot be kept within the fixing temperature margin range. In such a case, in order to use heater control to keep the fixing film temperatures in the heating regions belonging to the same drive group within the fixing temperature margin range, it is necessary to suppress the variation in the amount of heat generated in each heating region.

[0054] As a method for solving the effect of the above-mentioned variation in resistance value, a method of selecting heaters with less variation in heat generation during the manufacturing process is considered. However, this method has the risk of increasing the cost of the manufacturing process. Furthermore, even if heaters with less variation in heat generation are selected, it is difficult to eliminate the variation in heat generation. In other words, there is a demand for a mechanism that can replace or supplement the method of selecting heaters with less variation in heat generation during the manufacturing process.

[0055] <Heater Control in this Embodiment> Therefore, in this embodiment, the control unit switches the main thermistor used as the reference for temperature control between the start-up mode and the paper passing mode, thereby differentiating the temperature control of the fixing film 202. The heater control in this embodiment will be described below with reference to Figs. 8 and 9.

[0056] FIG. 8 is a flowchart of the process executed by CPU 420 in heater control in the same drive group when the recording material P is fixed by image heating device 200. FIG. 9 shows the temperature transition when heater control of this embodiment is performed in drive D2. FIG. 9(A) shows the transition of the detected temperature by main thermistor TM3 (dashed line) and main thermistor TM5 (solid line) of drive D2. The thermistor selected as the reference for temperature adjustment control to control the power supplied to drive D2 from main thermistor TM3 and main thermistor TM5 is shown by a thick line, and the control target temperature TGT2 of drive D2 is shown by a thick dashed line. FIG. 9(B) shows the temperature transition of areas TF3 and TF5 of fixing film 202 corresponding to heating areas HZ3 and HZ5.

[0057] [Extrusion Mode] In S601, the CPU 420 receives a print start command from the video controller 120 and the engine controller 113 controls each unit constituting the image forming apparatus 100 to start the image forming operation. The CPU 420 starts the power supply (hereinafter referred to as the heating operation) to the image heating apparatus 200 in response to the control by the engine controller 113. When the CPU 420 starts the heating operation of the image heating apparatus 200, the process proceeds to S602.

[0058] In S602, the CPU 420 selects the main thermistor (hereinafter referred to as Tmax) having the highest detected temperature among the main thermistors arranged in the same drive group as a reference thermistor for temperature adjustment control, and controls the power supply to the same drive group. The CPU 420 also sets the control target temperature TGT2 of Tmax to the upper limit target temperature Tlim. This is to raise the temperature of the fixing film 202 to the range of the fixing temperature margin as quickly as possible, as described above. Specifically, the CPU 420 selects TM5 (solid line) which is Tmax as a reference thermistor for temperature adjustment control, as shown in FIG. 9(A), and sets the control target temperature TGT2 of the drive D2 to the upper limit target temperature Tlim to control the power supply to the drive D2. After selecting the reference thermistor for temperature adjustment control and setting the control target temperature TGT2 of the drive D2, the CPU 420 advances the process to S603.

[0059] In S603, the CPU 420 executes the following process depending on whether the temperature detected by Tmax is equal to or greater than Tlim. If the temperature detected by Tmax is equal to or greater than Tlim, that is, if the temperature detected by TM5, which is Tmax, reaches Tlim, the CPU 420 advances the process to S604. If the temperature detected by Tmax is smaller than Tlim, that is, if the temperature detected by TM5, which is Tmax, does not reach Tlim, the process returns to S602. Note that if the heater continues to be heated even after the temperature detected by Tmax reaches the upper limit target temperature Tlim, the temperature of the fixing film 202 may exceed the fixing temperature margin. For this reason, in this embodiment, the control mode is shifted from the start-up mode to the paper passing mode at the timing when the temperature detected by Tmax reaches Tlim.

[0060] In this embodiment, this timing is the timing when the temperature detected by Tmax reaches Tlim, but it is not limited to this timing. For example, the control mode may be switched from the start-up mode to the paper passing mode at the timing when the recording material P reaches the fixing nip N. This is in consideration of the fact that the temperature of the heat generating block HB is taken by the recording material P as it passes through the heating areas (HZ1 to HZ7) in the paper passing mode. In this case, until the recording material P reaches the fixing nip N, the control target temperature of Tmax is controlled to be the upper limit target temperature Tlim, and the temperature detected by the main thermistor TM in the same drive group is controlled not to exceed the upper limit target temperature Tlim.

[0061] [Paper feed mode] In S604, if the CPU 420 is to start the paper passing mode or to continue the paper passing mode, the process proceeds to S605, and if the CPU 420 is to end the paper passing mode, the process proceeds to S608.

[0062] In S605, the CPU 420 selects the main thermistor (hereinafter referred to as Tmin) with the lowest detected temperature among the main thermistors arranged in the same drive group as the reference thermistor for temperature adjustment control, and controls the power supply to the same drive group. The CPU 420 also sets the control target temperature TGT2 of the drive D2 to Ttgt, using Tmin as the reference thermistor for temperature adjustment control. By setting the target temperature Ttgt to a temperature higher than the lower limit threshold temperature Tunder, the temperature detected by TM is controlled so as not to fall below the lower limit threshold temperature Tunder. Specifically, as shown in FIG. 9(A), the CPU 420 selects TM3 (broken line) which is Tmin as the reference thermistor for temperature adjustment control, and sets the control target temperature TGT2 of the drive D2 to Ttgt to control the power supply to the drive D2. After selecting the reference thermistor for temperature adjustment control and setting the control target temperature TGT2 of the drive D2, the CPU 420 advances the process to S606.

[0063] In S606, the CPU 420 monitors the detected temperature of the main thermistor arranged in the same drive group, and executes the next process depending on whether the detected temperature by Tmin is the same value as Ttgt. If the detected temperature by Tmin is the same value as Ttgt, that is, if the detected temperature by TM3 which is Tmin is the same value as Ttgt, the CPU 420 returns the process to S604 and executes the next process depending on whether or not to continue the paper passing mode. If the detected temperature by Tmin is not the same value as Ttgt, that is, if the detected temperature by TM3 which is Tmin is not the same value as Ttgt, the process proceeds to S607.

[0064] In S607, the CPU 420 controls the temperature detected by Tmin to be Ttgt. As an example of the process at this time, if the temperature detected by Tmin is higher than the value of Ttgt, the amount of power supply is reduced according to the difference between the temperature detected by Tmin and the value of Ttgt. Also, if the temperature detected by Tmin is lower than the value of Ttgt, the amount of power supply is increased according to the difference between the temperature detected by Tmin and the value of Ttgt. When the CPU 420 ends the control of the amount of power supply, the process returns to S604, and the next process is performed according to whether or not the paper passing mode is to be continued.

[0065] In S608, the paper passing mode is ended, and a description of the subsequent processing will be omitted.

[0066] As described above, in this embodiment, the control unit uses Tmax in the start-up mode and Tmin in the paper passing mode as the reference thermistor for temperature control. Also, in this embodiment, the CPU 420 selects Tmax and Tmin according to the temperature detected by the main thermistor. By controlling the heater in this manner, the temperatures of the areas TF3 and TF5 of the fixing film in the paper passing mode can be kept within the fixing temperature margin range, as shown in FIG. 9(B).

[0067] [Modification 1 of Example 1] In the first embodiment, when selecting the reference thermistor for temperature control in each of the start-up mode and the paper passing mode, the CPU 420 selects Tmax and Tmin as the reference thermistor for temperature control according to the detected temperature of the main thermistor. However, this embodiment is not limited to this method, and the CPU 420 may have a storage unit and store Tmax and Tmin detected in advance in the manufacturing process in the storage unit. By this method, in this embodiment, in the start-up mode, Tmax stored in the storage unit is used as the reference thermistor for temperature control, and the control target temperature TGT2 of the drive D2 is set to the upper limit target temperature Tlim. Also, in the paper passing mode, Tmin stored in the storage unit is used as the reference thermistor for temperature control, and the control target temperature TGT2 of the drive D2 is set to Ttgt.

[0068] When detecting Tmax and Tmin in advance in the manufacturing process, the heat generation amount of each heat generation block (HB1 to HB7) may be measured. In this case, a main thermistor that detects the temperature of the heat generation block with the maximum heat generation amount in the same drive group as Tmax and a main thermistor that detects the temperature of the heat generation block with the minimum heat generation amount in the same drive group as Tmin are stored in the memory unit.

[0069] In addition, when detecting Tmax and Tmin in advance in the manufacturing process, the resistance value of each heat generating block (HB1 to HB7) may be measured. In this case, a main thermistor that detects the temperature of the heat generating block with the smallest resistance value in the same drive group as Tmax and a main thermistor that detects the temperature of the heat generating block with the largest resistance value in the same drive group as Tmin are stored in a storage unit.

[0070] [Modification 2 of Example 1] In the first embodiment and the first modified example of the first embodiment, a method of selecting Tmax as the reference thermistor for temperature adjustment control in the start-up mode has been described. However, this is not the only method when the temperatures of all the main thermistors TM in the same drive group are monitored. In the start-up mode, all the heat values ​​of the heat generating blocks HB in the same drive group must be equal to or higher than the lower threshold temperature Tunder, and at that time, the heat value of the heat generating block HB must not exceed Ter. Therefore, first, the CPU 420 has a storage unit, and stores Tmax and Tmin detected in advance in the manufacturing process in the storage unit, and detects the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin. Then, the detected temperature of the main thermistor of the heat generating block HB that becomes Tmax is monitored. As a result, when the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin is smaller than the temperature difference between Tlim and Ttgt, no matter which main thermistor is selected as the reference thermistor for temperature adjustment control, when the detected temperature by Tmax reaches Tlim, the detected temperatures of all the main thermistors in the same drive group will exceed Ttgt. It is to be noted that ΔT is the difference between the temperature detected by Tmax and the temperature detected by Tmin when the temperature detected by Tmax reaches Tlim, and ΔT is constant throughout the paper passing mode.

[0071] For this reason, in this embodiment, Tmax does not necessarily have to be used as the reference thermistor for temperature control in the start-up mode. However, in the paper passing mode, in consideration of suppressing cold offset, Tmin is used as the reference thermistor for temperature control, and all heat values ​​of the heat generating blocks HB of the same driving group are controlled to be equal to or greater than Ttgt. This embodiment is similar to the first embodiment and the first modified example of the first embodiment in that the reference thermistor for temperature control and the control target temperature are switched between the start-up mode and the paper passing mode.

[0072] In the first embodiment and the first modification of the first embodiment, the heater control of the drive D2 as the same drive group is performed as an example, but in the present embodiment, a case where the heat generation amount varies in each heating area of ​​the drive D1 will be described. For example, a case where the heat generation amount of the heat generation block HB1 is the largest and the heat generation amount of the heat generation block HB7 is the smallest will be described.

[0073] <Heater Control in this Embodiment> The heater control in this embodiment will be described below with reference to FIG. 10 and FIG.

[0074] FIG. 10 is a flowchart of the process executed by the CPU 420 in heater control in the same drive group when the recording material P is fixed by the image heating device 200. FIG. 11 shows the temperature transition when the heater control of this embodiment is performed in the drive D1. FIG. 11(A) shows the transition of the detected temperature by the main thermistor TM7 (thin dashed line), main thermistor TM2 (dashed line), and main thermistor TM1 (solid line) of the drive D1. Among the main thermistors TM7, TM2, and TM1, the thermistor selected as the reference for temperature adjustment control to control the power supplied to the drive D1 is shown by a thick line, and the control target temperature TGT1 of the drive D1 is shown by a thick dashed line. FIG. 11(B) shows the temperature transition of the heating areas HZ7, HZ2, and TF7, TF2, and TF1 of the fixing film 202 corresponding to the heating areas HZ1.

[0075] [Extrusion Mode] In S1501, the CPU 420 receives a print start command from the video controller 120 and the engine controller 113 controls each unit constituting the image forming apparatus 100 to start the image forming operation. The CPU 420 starts the power supply (hereinafter referred to as the heating operation) to the image heating apparatus 200 in response to the control by the engine controller 113. When the CPU 420 starts the heating operation of the image heating apparatus 200, the process proceeds to S1502.

[0076] In S1502, the CPU 420 selects the main thermistor TM2 from among the main thermistors arranged in the same drive group as a reference thermistor for temperature adjustment control, and controls the power supply to the same drive group. The CPU 420 also sets the control target temperature TGT1 of the main thermistor TM2 to the upper limit target temperature Tlim. This is to raise the temperature of the fixing film 202 to the range of the fixing temperature margin as quickly as possible, as described above. Specifically, the CPU 420 selects the main thermistor TM2 (broken line) as a reference thermistor for temperature adjustment control, sets the control target temperature TGT1 of the drive D1 to the upper limit target temperature Tlim, and controls the power supply to the drive D1, as shown in FIG. 11(A). After selecting the reference thermistor for temperature adjustment control and setting the control target temperature TGT1 of the drive D1, the CPU 420 advances the process to S1503. The reference thermistor for temperature adjustment control selected at this time may be any of the main thermistors TM7, TM2, and TM1.

[0077] In S1503, the CPU 420 executes the following process depending on whether the detected temperature by Tmax is equal to or greater than Tlim. If the detected temperature by Tmax is equal to or greater than Tlim, that is, if the detected temperature by TM1, which is Tmax, reaches Tlim, the CPU 420 advances the process to S1504. If the detected temperature by Tmax is smaller than Tlim, that is, if the detected temperature by TM1, which is Tmax, does not reach Tlim, the process returns to S1502. At this time, the detected temperature by TM2 selected as the reference thermistor for temperature adjustment control may not reach Tlim, but since the difference between the detected temperature by TM1, which is Tmax, and the detected temperature by TM7, which is Tmin, is smaller than the difference between Tlim and Ttgt, the detected temperature by TM1, which is Tmax, reaches Tlim, and the detected temperature by TM7, which is Tmin, exceeds Ttgt. Note that, if the heater continues to be heated even after the detected temperature by Tmax reaches the upper limit target temperature Tlim, the temperature of the fixing film 202 may exceed the fixing temperature margin. For this reason, in this embodiment, the control mode is shifted from the start-up mode to the paper passing mode at the timing when the temperature detected by Tmax reaches Tlim.

[0078] In this embodiment, this timing is the timing when the temperature detected by Tmax reaches Tlim, but it is not limited to this timing. For example, the control mode may be switched from the start-up mode to the paper passing mode at the timing when the recording material P reaches the fixing nip N. This is in consideration of the fact that the temperature of the heat generating block HB is taken by the recording material P as it passes through the heating areas (HZ1 to HZ7) in the paper passing mode. In this case, until the recording material P reaches the fixing nip N, the control target temperature of Tmax is controlled to be the upper limit target temperature Tlim, and the temperature detected by the main thermistor TM in the same drive group is controlled not to exceed the upper limit target temperature Tlim.

[0079] [Paper feed mode] In S1504, if the CPU 420 is to start the paper passing mode or to continue the paper passing mode, the process proceeds to S1505, and if the CPU 420 is to end the paper passing mode, the process proceeds to S1508.

[0080] In S1505, the CPU 420 selects the main thermistor (hereinafter referred to as Tmin) having the lowest detected temperature among the main thermistors arranged in the same drive group as the reference thermistor for temperature adjustment control, and controls the power supply to the same drive group. The CPU 420 also sets the control target temperature TGT1 of the drive D1 to Ttgt, using Tmin as the reference thermistor for temperature adjustment control. As described above, Ttgt is a temperature set so that the temperature of the fixing film 202 does not fall below the lower limit temperature Tbu of the fixing temperature margin. Specifically, as shown in FIG. 11(A), the CPU 420 selects TM7 (thin broken line) which is Tmin as the reference thermistor for temperature adjustment control, sets the control target temperature TGT1 of the drive D1 to Ttgt, and controls the power supply to the drive D1. After selecting the reference thermistor for temperature adjustment control and setting the control target temperature TGT1 of the drive D1, the CPU 420 advances the process to S1506.

[0081] In S1506, the CPU 420 monitors the detected temperature of the main thermistor arranged in the same drive group, and executes the next process depending on whether the detected temperature by Tmin is the same value as Ttgt. If the detected temperature by Tmin is the same value as Ttgt, that is, if the detected temperature by TM7 which is Tmin is the same value as Ttgt, the CPU 420 returns the process to S1504, and executes the next process depending on whether or not to continue the paper passing mode. If the detected temperature by Tmin is not the same value as Ttgt, that is, if the detected temperature by TM7 which is Tmin is not the same value as Ttgt, the process proceeds to S1507.

[0082] In S1507, the CPU 420 controls the temperature detected by Tmin to be Ttgt. As an example of the process at this time, if the temperature detected by Tmin is higher than the value of Ttgt, the amount of power supply is reduced according to the difference between the temperature detected by Tmin and the value of Ttgt. Also, if the temperature detected by Tmin is lower than the value of Ttgt, the amount of power supply is increased according to the difference between the temperature detected by Tmin and the value of Ttgt. When the CPU 420 ends the control of the amount of power supply, the process returns to S1504, and the next process is performed according to whether or not the paper passing mode is to be continued.

[0083] In S1508, the paper passing mode is ended, and a description of the subsequent processing will be omitted.

[0084] As described above, in this embodiment, the following heater control method is used as an alternative to or supplementary to the method of selecting two or more heat generating blocks with little variation in heat generation during the manufacturing process. That is, the control unit switches the main thermistor used as the reference for temperature control between the start-up mode and the paper passing mode, and causes the temperature control of the fixing film 202 to differ. This method makes it possible to keep the film temperature in the heating areas belonging to the same drive group within the fixing temperature margin range while suppressing increases in manufacturing costs and decreases in accuracy. EXAMPLES

[0085] In the first embodiment, as a heater control method, a method of switching the main thermistor used as a reference for temperature control between the start-up mode and the paper passing mode by the control unit has been described. In this embodiment, as shown by the thick solid line in FIG. 13(A), Tmax is used as a reference thermistor for temperature control throughout the start-up mode and the paper passing mode, and the control target temperature TGT2 of the drive D2 is set according to the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin, which is different from the first embodiment. In this embodiment, Tmax is also used as a reference thermistor for temperature control in the paper passing mode. For this reason, in the paper passing mode, the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin is measured in advance in the manufacturing process so that the detected temperature by Tmin does not fall below the lower limit threshold temperature Tunder. Then, Tmax is used as a reference thermistor for temperature control, and the control target temperature TGT2 of the drive D2 is set to Ttgt+ΔT. At this time, in consideration of suppressing cold offset, Tmax may be used as a reference thermistor for temperature adjustment control, and the control target temperature TGT2 of the drive D2 may be set to a temperature higher than Ttgt+ΔT.

[0086] In addition, if a non-paper passing portion temperature rise occurs in the heat generating block where Tmax is arranged, the value of the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin will differ from the value of ΔT measured in advance in the manufacturing process. Even in this case, if the heater control according to this embodiment is executed, the detected temperature by Tmin may fall below Ttgt. Therefore, in this embodiment, in consideration of suppressing cold offset, the heater control according to this embodiment is executed only when a non-paper passing portion temperature rise does not occur at Tmax. For example, after executing image formation on small size paper where a non-paper passing portion temperature rise may occur, the heater control according to this embodiment is not executed.

[0087] Heater control in this embodiment will be described below with reference to Figures 12 and 13. In the following description, the same components as those in the first embodiment will be given the same reference numbers and the description thereof will be omitted.

[0088] FIG. 12 is a flowchart of the process executed by the CPU 420 in heater control in the same driving group in this embodiment. FIG. 13 shows the temperature transition when the heater control of this embodiment is performed in the drive D2. FIG. 13(A) shows the transition of the temperature detected by the main thermistor TM3 (dashed line) and the main thermistor TM5 (solid line) of the drive D2. The thermistor selected as the reference for temperature adjustment control to control the power supplied to the drive D2 from the main thermistor TM3 and the main thermistor TM5 is shown by a thick line, and the control target temperature TGT2 of the drive D2 is shown by a thick dashed line. FIG. 13(B) shows the temperature transition of the areas TF3 and TF5 of the fixing film 202 corresponding to the heating areas HZ3 and HZ5.

[0089] [Extrusion Mode] In S1101, a print start command is sent from video controller 120 to engine controller 113, whereby engine controller 113 controls each unit constituting image forming apparatus 100 to start an image forming operation. CPU 420 starts the heating operation of image heating apparatus 200 in response to control by engine controller 113. When CPU 420 starts the heating operation of image heating apparatus 200, it advances the process to S1102.

[0090] In S1102, the CPU 420 selects the main thermistor Tmax having the highest detected temperature, which was detected in advance in the manufacturing process, among the main thermistors arranged in the same drive group, as the reference thermistor for temperature adjustment control, and controls the power supply to the same drive group. At this time, the CPU 420 may detect the main thermistor Tmax having the highest detected temperature among the main thermistors arranged in the same drive group, and select it as the reference thermistor for temperature adjustment control. The CPU 420 also uses Tmax as the reference thermistor for temperature adjustment control, and sets the control target temperature TGT2 of the drive D2 to the upper limit temperature Tlim. Specifically, the CPU 420 selects TM5 (solid line), which is Tmax, as the reference thermistor for temperature adjustment control, as shown in FIG. 13(A), and controls the power supply to the drive D2 by setting the control target temperature TGT2 of the drive D2 to the upper limit target temperature Tlim. The CPU 420 selects a reference thermistor for temperature regulation and sets the control target temperature TGT2 of the drive D2, and then advances the process to 1103.

[0091] In S1103, the CPU 420 executes the following process depending on whether the detected temperature by Tmax is equal to or greater than Tlim. If the detected temperature by Tmax is equal to or greater than Tlim, that is, if the detected temperature by TM5, which is Tmax, has reached Tlim, the CPU 420 advances the process to S1104. If the detected temperature by Tmax is smaller than Tlim, that is, if the detected temperature by TM5, which is Tmax, has not reached Tlim, the CPU 420 returns the process to S1102.

[0092] [Paper feed mode] In S1104, if the CPU 420 is to start the paper passing mode or to continue the paper passing mode, the process proceeds to S1105, and if the CPU 420 is to end the paper passing mode, the process proceeds to S1108.

[0093] In S1105, the CPU 420 continues to control the power supply to the same drive group using Tmax as the reference thermistor for temperature adjustment control. At this time, as described above, Tmax is used as the reference thermistor for temperature adjustment control, and the target temperature TGT2 of the drive D2 is set to Ttgt+ΔT. Specifically, as shown in FIG. 13(A), the CPU 420 selects TM5 (solid line), which is Tmax, as the reference thermistor for temperature adjustment control, and sets the control target temperature TGT2 of the drive D2 to Ttgt+ΔT to control the power supply to the drive D2. After setting the control target temperature TGT2 of the drive D2, the CPU 420 advances the process to S1106.

[0094] In S1106, the CPU 420 monitors the detected temperature of the main thermistor arranged in the same drive group, and executes the next process depending on whether the detected temperature by Tmax is the same value as Ttgt+ΔT. If the detected temperature by Tmax is the same value as Ttgt+ΔT, that is, if the detected temperature by TM5 which is Tmax is the same value as Ttgt+ΔT, the CPU 420 returns the process to S1104, and executes the next process depending on whether or not to continue the paper passing mode. If the detected temperature by Tmax is not the same value as Ttgt+ΔT, that is, if the detected temperature by TM5 which is Tmax is not the same value as Ttgt+ΔT, the process proceeds to S1107.

[0095] In S1107, the CPU 420 controls the temperature detected by Tmax to be Ttgt+ΔT. As an example of the process at this time, if the temperature detected by Tmax is higher than the value of Ttgt+ΔT, the amount of power supply is reduced according to the difference between the temperature detected by Tmax and the value of Ttgt+ΔT. Also, if the temperature detected by Tmax is lower than the value of Ttgt+ΔT, the amount of power supply is increased according to the difference between the temperature detected by Tmax and the value of Ttgt+ΔT. When the CPU 420 ends the control of the amount of power supply, the process returns to S1104, and the next process is executed according to whether or not the paper passing mode is continued.

[0096] In S1108, the paper passing mode is ended. A description of the subsequent processes will be omitted.

[0097] As described above, in this embodiment, Tmax is used as the reference thermistor for temperature control throughout the start-up mode and the paper passing mode, and the control target temperature TGT2 of the drive D2 is set according to the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin. Note that ΔT is the difference between the detected temperature by Tmax and the detected temperature by Tmin when the detected temperature by Tmax reaches Tlim, and ΔT is constant throughout the paper passing mode. By controlling the heater in this manner, the temperatures of the areas TF3 and TF5 of the fixing film in the paper passing mode can be kept within the fixing temperature margin range, as shown in FIG. 13(B).

[0098] In this embodiment, the control target temperature TGT2 of the drive D2 is set according to the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin, but the difference ΔT does not necessarily have to be used. For example, the ratio of the detected temperature by Tmax to the detected temperature by Tmin may be used to control the heater so that the detected temperature by the main thermistors TM3 and TM5 falls within the range of the fixing temperature margin. That is, the control target temperature TGT2 is set corrected based on a coefficient according to the detected temperature by Tmax and the detected temperature by Tmin. As an example of control in this case, it is assumed that the detected temperature by Tmax is equal to 1.1 times the detected temperature by Tmin. In this case, when TM5 is used as the thermistor based on which the temperature control is performed, the control target temperature TGT2 in the paper passing mode is set to Ttgt×1.1 in this embodiment.

[0099] As an example of control using the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin, when the detected temperature by Tmin is equal to the detected temperature by Tmax minus 5° C., the detected temperature by Tmax minus 5° C. may be controlled to be the detected temperature by Tmin. In this case, in the paper passing mode, the detected temperature by Tmax minus 5° C. is controlled to be the target temperature Ttgt.

[0100] Furthermore, as an example of control using the ratio of the detected temperature by Tmax to the detected temperature by Tmin, when the detected temperature by Tmin is equal to 0.9 times the detected temperature by Tmax, the detected temperature by Tmax multiplied by 0.9 may be controlled as the detected temperature by Tmin. In this case, in the paper passing mode, the detected temperature by Tmax multiplied by 0.9 is controlled to become the target temperature Ttgt.

[0101] The difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin, and the ratio between the detected temperature by Tmax and the detected temperature by Tmin are also referred to as information on the temperature difference between the first detected temperature and the second detected temperature. In addition, the heater may be controlled so that the detected temperature by the main thermistors TM3 and TM5 falls within the fixing temperature margin by comparing information on the heat generation amount of the heat generation block HB at Tmax and the heat generation block HB at Tmin. The information on the heat generation amount in this case may be a value based on the actual measured values ​​of the detected temperatures by Tmax and Tmin during the manufacturing process and image formation, or may be based on values ​​related to the detected temperatures by Tmax and Tmin predicted based on environmental factors during image formation. EXAMPLES

[0102] In the second embodiment, Tmax is used as the reference thermistor for temperature control throughout the start-up mode and the paper passing mode, and the control target temperature TGT2 of the drive D2 is set according to the difference ΔT between the temperature detected by Tmax and the temperature detected by Tmin. This embodiment differs from the second embodiment in that Tmin is used as the reference thermistor for temperature control throughout the start-up mode and the paper passing mode, as shown by the thick dotted line in FIG. 15(A). In this embodiment, Tmin is used as the reference thermistor for temperature control even in the start-up mode. For this reason, in the start-up mode, the difference ΔT between the temperature detected by Tmax and the temperature detected by Tmin is measured in advance during the manufacturing process so that the temperature detected by Tmax does not exceed Tlim. Then, Tmin is used as the reference thermistor for temperature control, and the control target temperature TGT2 of the drive D2 is set to Tlim-ΔT. At this time, in consideration of safety, Tmin may be used as the reference thermistor for temperature control, and the control target temperature TGT2 of the drive D2 may be set to a temperature lower than Tlim-ΔT.

[0103] Furthermore, if a non-paper passing section temperature rise occurs in the heat generating block where Tmax is located, the value of the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin will differ from the value of ΔT measured in advance in the manufacturing process. Even in this case, if the heater control according to this embodiment is executed, the detected temperature by Tmax may exceed the value of Ter. For this reason, in this embodiment, in consideration of safety, the heater control according to this embodiment is executed only when a non-paper passing section temperature rise does not occur at Tmax. For example, after executing image formation on small size paper where a non-paper passing section temperature rise may occur, the heater control according to this embodiment is not executed.

[0104] Heater control in this embodiment will be described below with reference to Figures 14 and 15. In the following description, the same components as those in the first embodiment will be given the same reference numbers and the description thereof will be omitted.

[0105] FIG. 14 is a flowchart of the process executed by the CPU 420 in heater control in the same driving group in this embodiment. FIG. 15 shows the temperature transition when the heater control of this embodiment is performed in the drive D2. FIG. 15(A) shows the transition of the temperature detected by the main thermistor TM3 (dashed line) and the main thermistor TM5 (solid line) of the drive D2. The thermistor selected as the reference for temperature adjustment control to control the power supplied to the drive D2 from the main thermistor TM3 and the main thermistor TM5 is shown by a thick line, and the control target temperature TGT2 of the drive D2 is shown by a thick dashed line. FIG. 15(B) shows the temperature transition of the areas TF3 and TF5 of the fixing film 202 corresponding to the heating areas HZ3 and HZ5.

[0106] [Extrusion Mode] In S1301, a print start command is sent from video controller 120 to engine controller 113, whereby engine controller 113 controls each unit constituting image forming apparatus 100 to start an image forming operation. CPU 420 starts the heating operation of image heating apparatus 200 in response to control by engine controller 113. When CPU 420 starts the heating operation of image heating apparatus 200, it advances the process to S1302.

[0107] In S1302, the CPU 420 selects the main thermistor Tmax having the highest detected temperature, which was detected in advance in the manufacturing process, among the main thermistors arranged in the same drive group, as the reference thermistor for temperature adjustment control, and controls the power supply to the same drive group. At this time, the CPU 420 may detect the main thermistor Tmin having the lowest detected temperature among the main thermistors arranged in the same drive group, and select it as the reference thermistor for temperature adjustment control. The CPU 420 also uses Tmin as the reference thermistor for temperature adjustment control, and sets the control target temperature TGT2 of the drive D2 to Ttgt. Specifically, the CPU 420 selects TM3 (dashed line) which is Tmin, as the reference thermistor for temperature adjustment control, as shown in FIG. 15(A). At this time, as described above, when Tmin is used as a reference thermistor for temperature adjustment control so that the temperature detected by Tmax does not exceed Tlim, the control target temperature TGT2 of the drive D2 is set to the upper limit target temperature Tlim-ΔT to control the power supply to the drive D2. The CPU 420 selects a reference thermistor for temperature adjustment control, sets the control target temperature TGT2 of the drive D2, and proceeds to process 1303.

[0108] In S1303, the CPU 420 executes the following process depending on whether the detected temperature by Tmin is equal to or greater than Tlim-ΔT. If the detected temperature by Tmax is equal to or greater than Tlim, that is, if the detected temperature by TM3, which is Tmin, has reached Tlim-ΔT, the CPU 420 advances the process to S1304. If the detected temperature by Tmax is smaller than Tlim, that is, if the detected temperature by TM3, which is Tmin, has not reached Tlim-ΔT, the CPU 420 returns the process to S1302.

[0109] [Paper feed mode] In S1304, if the CPU 420 is to start the paper passing mode or to continue the paper passing mode, the process proceeds to S1305, and if the CPU 420 is to end the paper passing mode, the process proceeds to S1308.

[0110] In S1305, the CPU 420 continues to control the power supply to the same drive group using Tmin as the reference thermistor for temperature adjustment control. At this time, Tmin is used as the reference thermistor for temperature adjustment control, and the control target temperature TGT2 of the drive D2 is set to Ttgt. Specifically, as shown in FIG. 15(A), the CPU 420 selects TM3 (dashed line), which is Tmin, as the reference thermistor for temperature adjustment control, and sets the control target temperature TGT2 of the drive D2 to Ttgt to control the power supply to the drive D2. After setting the control target temperature TGT2 of the drive D2, the CPU 420 advances the process to S1306.

[0111] In S1306, the CPU 420 monitors the detected temperature of the main thermistor arranged in the same drive group throughout the paper passing mode, and executes the next process depending on whether the detected temperature by Tmin is the same value as Ttgt. If the detected temperature by Tmin is the same value as Ttgt, that is, if the detected temperature by TM3 which is Tmin is the same value as Ttgt, the CPU 420 returns the process to S1304 and executes the next process depending on whether the paper passing mode is to be continued. If the detected temperature by Tmin is not the same value as Ttgt, that is, if the detected temperature by TM3 which is Tmin is not the same value as Ttgt, the process proceeds to S1307.

[0112] In S1307, the CPU 420 controls the temperature detected by Tmin to be Ttgt. As an example of the process at this time, if the temperature detected by Tmin is higher than the value of Ttgt, the amount of power supply is reduced according to the difference between the temperature detected by Tmin and the value of Ttgt. Also, if the temperature detected by Tmin is lower than the value of Ttgt, the amount of power supply is increased according to the difference between the temperature detected by Tmin and the value of Ttgt. When the CPU 420 ends the control of the amount of power supply, the process returns to S1104, and the next process is performed according to whether or not the paper passing mode is to be continued.

[0113] In S1108, the paper passing mode is ended. A description of the subsequent processes will be omitted.

[0114] As described above, in this embodiment, Tmin is used as the reference thermistor for temperature control throughout the start-up mode and the paper passing mode, and the control target temperature TGT2 of the drive D2 is set according to the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin. Note that ΔT is the difference between the detected temperature by Tmax and the detected temperature by Tmin when the detected temperature by Tmax reaches Tlim, and ΔT is constant throughout the paper passing mode. By controlling the heater in this manner, the temperatures of the areas TF3 and TF5 of the fixing film in the paper passing mode can be kept within the fixing temperature margin range, as shown in FIG. 15(B).

[0115] In this embodiment, the control target temperature TGT2 of the drive D2 is set according to the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin, but the difference ΔT does not necessarily have to be used. For example, the ratio of the detected temperature by Tmax to the detected temperature by Tmin may be used to control the heater so that the detected temperature by the main thermistors TM3 and TM5 falls within the range of the fixing temperature margin. That is, the control target temperature TGT2 is set corrected based on a coefficient according to the detected temperature by Tmax and the detected temperature by Tmin. As an example of control in this case, it is assumed that the detected temperature by Tmax is equal to 1.1 times the detected temperature by Tmin. In this case, when TM3 is used as the thermistor based on the temperature adjustment control, the control target temperature TGT2 in the start-up mode is set to Tlim×0.9 in this embodiment. The difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin and the ratio of the detected temperature by Tmax to the detected temperature by Tmin are also referred to as information on the temperature difference between the first detected temperature and the second detected temperature.

[0116] As an example of control using the difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin, when the detected temperature by Tmax is equal to the detected temperature by Tmin plus 5° C., the detected temperature by Tmin plus 5° C. may be controlled to be the detected temperature by Tmax. In this case, in the start-up mode, the detected temperature by Tmin plus 5° C. is controlled to become the target temperature Tlim.

[0117] Furthermore, as an example of control using the ratio of the detected temperature by Tmax to the detected temperature by Tmin, when the detected temperature by Tmax is equal to 1.1 times the detected temperature by Tmin, the detected temperature by Tmin may be multiplied by 1.1 to be the detected temperature by Tmax. In this case, in the start-up mode, the detected temperature by Tmin is controlled to be multiplied by 1.1 to be the target temperature Tlim.

[0118] The difference ΔT between the detected temperature by Tmax and the detected temperature by Tmin, and the ratio between the detected temperature by Tmax and the detected temperature by Tmin are also referred to as information on the temperature difference between the first detected temperature and the second detected temperature. In addition, the heater may be controlled so that the detected temperature by the main thermistors TM3 and TM5 falls within the fixing temperature margin by comparing information on the heat generation amount of the heat generation block HB at Tmax and the heat generation block HB at Tmin. The information on the heat generation amount in this case may be a value based on the actual measured values ​​of the detected temperatures by Tmax and Tmin during the manufacturing process and image formation, or may be based on values ​​related to the detected temperatures by Tmax and Tmin predicted based on environmental factors during image formation. EXAMPLES

[0119] In this embodiment, the heating block HB5 generates a larger amount of heat than HB3, and in addition, a small-sized recording material is passed to one side immediately before, and the heater control of this embodiment is applied in a state where the influence of the asymmetrical temperature rise in the non-passing portion in the longitudinal direction remains. In this case, the passing to one side means that the small-sized recording material is placed in the paper feed cassette 15A with the longitudinal center position (not shown) shifted to the left or right from the transport reference position X, and image formation is performed. In this embodiment, a B5-sized sheet is placed against a regulating plate (not shown) on the right side of the longitudinal direction of the paper feed cassette 15A, and image formation is performed in a state where the heating area HZ3 is the non-passing portion and the heating area HZ5 is the passing portion.

[0120] Fig. 16 shows the temperature transition when the heater control of this embodiment is performed in the drive D2. Fig. 16(A) in this embodiment shows the temperature transition of the main thermistor TM3 (dashed line) and the main thermistor TM5 (solid line) of the drive D2. Of the main thermistors TM3 and TM5, the thermistor selected as the reference for controlling the power supplied to the drive D2 is shown by a thick line, and the control target temperature TGT2 of the drive D2 is shown by a thick dashed line. Fig. 16(B) shows the temperature transition of the regions TF3 and TF5 of the fixing film 202 corresponding to the heating regions HZ3 and HZ5.

[0121] 16A, image formation is started in a state where the temperature detected by main thermistor TM3 is higher than the temperature detected by main thermistor TM5. For a while after image formation is started, the temperature detected by main thermistor TM3 remains higher than the temperature detected by main thermistor TM5 due to the influence of the temperature rise in the non-paper passing area. After that, when the first sheet of recording material P reaches the fixing nip N, the temperature difference caused by the resistance variation of the heat generating block gradually becomes larger than the temperature difference caused by the temperature rise in the non-paper passing area, and the temperature detected by main thermistor TM5 becomes higher than the temperature detected by main thermistor TM3.

[0122] Next, the heater control executed by CPU 420 in response to the temperature transition of the main thermistor as shown in FIG. 16(A) will be described by extracting the heater control process shown in the flowchart of FIG.

[0123] <Launch mode> In S602, because the temperature detected by TM3 is higher than the temperature detected by TM5, the CPU 420 selects TM3 (dashed line) as the reference thermistor for Tmax, sets the control target temperature TGT2 of the drive D2 to the upper target temperature Tlim, and controls the power supply to the drive D2 so that the overheating threshold Ter is not exceeded. After selecting the reference thermistor and setting the control target temperature TGT2 of the drive D2, the CPU 420 advances the process to S603.

[0124] In S603, when the temperature detected by Tmax becomes equal to or higher than Tlim, that is, when the temperature detected by TM3 which is Tmax reaches Tlim, the CPU 420 advances the process to S604 and the control mode transitions to the paper passing mode.

[0125] <Paper feed mode> In S604, if the CPU 420 is to start the paper passing mode or to continue the paper passing mode, the process proceeds to S605, and if the CPU 420 is to end the paper passing mode, the process proceeds to S608.

[0126] In S605, because the temperature detected by TM5 is lower than the temperature detected by TM3, the CPU 420 selects TM5 (solid line) as the reference thermistor for Tmin and controls the power supply to the drive D2. The CPU 420 also uses Tmin as the reference thermistor and sets the control target temperature TGT2 of the drive D2 to Ttgt. After selecting the reference thermistor and setting the control target temperature TGT2 of the drive D2, the CPU 420 advances the process to S606.

[0127] In S606, the CPU 420 monitors the detected temperature of the main thermistor arranged in the same drive group, and executes the next process depending on whether the detected temperature by Tmin is the same value as Ttgt. If the detected temperature by Tmin is the same value as Ttgt, that is, if the detected temperature by TM5 which is Tmin is equal to or higher than Ttgt, the CPU 420 advances the process to S606 and continues the heating operation of the image heating apparatus 200. Also, if the detected temperature by Tmin is below Ttgt, that is, if the detected temperature by TM3 which is Tmin is below Ttgt, the process returns to S604. In this embodiment, at timing A in FIG. 16, the detected temperature by TM3 is below the detected temperature by TM5, and the magnitude relationship of the temperatures is reversed. For this reason, the CPU 420 selects TM3 (dashed line) as the reference thermistor for Tmin, and controls the power supply to the drive D2.

[0128] Although the image forming operation and the heating operation continue in the processing from S606 onwards, the description thereof will be omitted in this embodiment.

[0129] In this embodiment, the control unit uses Tmax as the reference thermistor in the start-up mode and Tmin as the reference thermistor in the paper passing mode. Also, in this embodiment, the CPU 420 selects Tmax and Tmin according to the temperature detected by the main thermistor. By controlling the heater in this manner, the temperatures of the fixing film areas TF3 and TF5 in the paper passing mode can be kept within the fixing temperature margin range, as shown in FIG. 16(B).

[0130] [Other Examples] In the first to fourth embodiments, a state in which the resistance value of the heat generating block HB5 is smaller than that of the heat generating block HB3 and the heat generation amount of the heat generating block HB5 is larger than that of the heat generating block HB3 has been described as an example. However, this embodiment is not limited to this example. For example, the heat generation amount of the heat generating block HB3 may be larger than that of the heat generating block HB5. In this case, when the CPU 420 performs the same control as in the first embodiment, in the start-up mode, TM3 with Tmax is selected as the reference thermistor. Also, in the paper passing mode, TM5 with Tmin is selected as the reference thermistor.

[0131] Furthermore, in the first embodiment, the timing for switching the thermistor used to control the same drive group from Tmax to Tmin (the timing for transitioning from the start-up mode to the paper passing mode) is set to the same timing as the timing for switching the control target temperature from Tlim to Ttgt. However, this timing is not necessarily limited to this, and it may be set to, for example, the timing when the first recording material P enters the fixing nip N.

[0132] Furthermore, in the first to fourth embodiments, the sub-thermistors TS2 to TS6 are not used for controlling the power supply, but these thermistors may also be included in the selection of Tmax and Tmin. [Explanation of symbols]

[0133] 100 Image forming device 200 Image heating device 300 Heater HZ1~HZ7 Heating area HB1~HB7 Heating Block

Claims

1. An image heating device for heating an image formed on a recording material, comprising: a heater in which a plurality of heat generating blocks, including a first heat generating block and a second heat generating block having a resistance value different from that of the first heat generating block, are arranged in a direction perpendicular to a conveying direction of a recording material; a first temperature detection member that is provided in an area overlapping the first heat generating block when the heater is viewed in a thickness direction of the heater, and detects a temperature of the first heat generating block; a second temperature detection member that is provided in a region overlapping the second heat generating block when the heater is viewed in a thickness direction of the heater and detects a temperature of the second heat generating block; A control unit that controls the supply of power to the plurality of heat generating blocks; Equipped with the first heat generating block and the second heat generating block are electrically connected to a common power supply path; the control unit controls the power supplied to the common power supply path in response to a first detected temperature detected by the first temperature detection member or a second detected temperature detected by the second temperature detection member; If a period from when the supply of power to the common power supply path is started until one of the first detected temperature and the second detected temperature reaches a first temperature that is a control target temperature for a start-up period is defined as a first period, and a period during which the recording material is heated by the heater after the one of the first detected temperature and the second detected temperature reaches the first temperature is defined as a second period, the control unit uses the selected first temperature detection member to control the power supplied to the common power supply path during the first period, and uses the selected second temperature detection member to control the power supplied to the common power supply path during the second period; the first temperature detecting member has a higher detection temperature than the second temperature detecting member; During the second period, the first detected temperature and the second detected temperature are within a range between the first temperature and a second temperature which is set to be lower than the first temperature so as not to cause a heating defect in an image formed on a recording material. An image heating device comprising:

2. 2. The image heating apparatus according to claim 1, wherein the control unit controls the second detected temperature to become a third temperature that is lower than the first temperature and higher than the second temperature, so that neither the first detected temperature nor the second detected temperature falls below the second temperature during the second period.

3. 3. The image heating apparatus according to claim 2, wherein the control unit raises the temperature of the heater by controlling the power supplied to the common power supply path so that the temperature detection member having the higher detected temperature reaches the first temperature during the first period, and controls the power supplied to the common power supply path so that the temperature detection member having the lower detected temperature reaches the third temperature during the second period, thereby keeping the first detected temperature and the second detected temperature between the first temperature and the second temperature.

4. 4. An image heating apparatus according to claim 1, wherein the control unit controls the power supplied to the common power supply path by selecting, during the first period, the first temperature detection member or the second temperature detection member, which has a higher detected temperature, and by selecting, during the second period, the second temperature detection member or the first temperature detection member or the second temperature detection member, which has a lower detected temperature.

5. a storage unit that stores the first temperature detection member having a higher detection temperature among the first temperature detection member and the second temperature detection member, and the second temperature detection member having a lower detection temperature among the first temperature detection member and the second temperature detection member, 4. The image heating apparatus according to claim 1, wherein the control unit controls the power supplied to the common power supply path during the first period using the first temperature detection member having the higher detected temperature stored in the memory unit, and controls the power supplied to the common power supply path during the second period using the second temperature detection member having the lower detected temperature stored in the memory unit.

6. An image heating device for heating an image formed on a recording material, comprising: a heater in which a plurality of heat generating blocks including a first heat generating block and a second heat generating block having a smaller heat generation amount than the first heat generating block are arranged in a direction perpendicular to a conveying direction of a recording material; a first temperature detection member that is provided in an area overlapping the first heat generating block when the heater is viewed in a thickness direction of the heater, and detects a temperature of the first heat generating block; a second temperature detection member that is provided in a region overlapping the second heat generating block when the heater is viewed in a thickness direction of the heater and detects a temperature of the second heat generating block; A control unit that controls the supply of power to the plurality of heat generating blocks; Equipped with the first heat generating block and the second heat generating block are electrically connected to a common power supply path; The control unit controls power supplied to the common power supply path, If a period from when the supply of power to the common power supply path is started until a first detected temperature by a first temperature detection member reaches a first temperature that is a control target temperature for a start-up period is defined as a first period, and a period during which the recording material is heated by the heater after the first detected temperature reaches the first temperature is defined as a second period, the control unit controls, during the first period, the power supplied to the common power supply path in response to the first detected temperature, and during the second period, controls the power supplied to the common power supply path in response to the first detected temperature and information regarding a temperature difference between the first detected temperature and a second detected temperature detected by the second temperature detection member; an image heating device characterized in that, during the second period, the first detection temperature and the second detection temperature fall within a temperature range between the first temperature and a second temperature which is set to be lower than the first temperature so as not to cause heating defects in an image formed on a recording material.

7. 7. The image heating apparatus according to claim 6, wherein the control unit controls the power supplied to the common power supply path so that, during the second period, the first detected temperature becomes a third temperature that is lower than the first temperature and higher than the second temperature plus a temperature difference between the first detected temperature and the second detected temperature.

8. 7. The image heating apparatus according to claim 6, wherein the control unit controls the power supplied to the common power supply path so that, during the second period, a temperature obtained by subtracting a temperature difference between the first detected temperature and the second detected temperature from the first detected temperature becomes a third temperature that is lower than the first temperature and higher than the second temperature.

9. 7. The image heating apparatus according to claim 6, wherein the control unit controls the power supplied to the common power supply path so that, during the second period, the first detected temperature becomes a third temperature that is lower than the first temperature and higher than the second temperature, corrected based on a coefficient corresponding to a temperature difference between the first detected temperature and the second detected temperature.

10. 7. The image heating apparatus according to claim 6, wherein the control unit controls the power supplied to the common power supply path so that a temperature obtained by correcting the first detected temperature based on a coefficient corresponding to a temperature difference between the first detected temperature and the second detected temperature during the second period becomes a third temperature.

11. a heater in which a plurality of heat generating blocks including a first heat generating block and a second heat generating block having a smaller heat generation amount than the first heat generating block are arranged in a direction perpendicular to a conveying direction of a recording material; a first temperature detection member that is provided in an area overlapping the first heat generating block when the heater is viewed in a thickness direction of the heater, and detects a temperature of the first heat generating block; a second temperature detection member that is provided in a region overlapping the second heat generating block when the heater is viewed in a thickness direction of the heater and detects a temperature of the second heat generating block; A control unit that controls the supply of power to the plurality of heat generating blocks; Equipped with the first heat generating block and the second heat generating block are electrically connected to a common power supply path; The control unit controls power supplied to the common power supply path, If a period from when the supply of power to the common power supply path is started until a first detected temperature by a first temperature detection member reaches a first temperature that is a control target temperature for a start-up period is defined as a first period, and a period during which the recording material is heated by the heater after the first detected temperature reaches the first temperature is defined as a second period, the control unit controls, during the first period, power to be supplied to the common power supply path in response to information regarding a temperature difference between the first detected temperature and a second detected temperature detected by the second temperature detection member and the second detected temperature, and controls, during the second period, power to be supplied to the common power supply path in response to the second detected temperature; an image heating device characterized in that, during the second period, the second detected temperature falls within a temperature range between the first temperature and a second temperature which is a temperature lower than the first temperature and set so as not to cause heating defects in an image formed on a recording material.

12. 12. The image heating apparatus according to claim 11, wherein the control unit controls the power supplied to the common power supply path so that, during the first period, the second detected temperature becomes a temperature obtained by subtracting a temperature difference between the first detected temperature and the second detected temperature from the first temperature.

13. 12. The image heating apparatus according to claim 11, wherein the control unit controls the power supplied to the common power supply path so that a temperature obtained by adding a temperature difference between the first detected temperature and the second detected temperature to the second detected temperature during the first period becomes the first temperature.

14. 12. The image heating apparatus according to claim 11, wherein the control unit controls the power supplied to the common power supply path so that, during the first period, the second detected temperature becomes a temperature obtained by correcting the first temperature based on a coefficient corresponding to a temperature difference between the first detected temperature and the second detected temperature.

15. 12. The image heating apparatus according to claim 11, wherein the control unit controls the power supplied to the common power supply path so that a temperature obtained by correcting the second detected temperature based on a coefficient corresponding to a temperature difference between the first detected temperature and the second detected temperature during the first period becomes the first temperature.

16. An image heating device for heating an image formed on a recording material, comprising: a heater in which a plurality of heat generating blocks including a first heat generating block and a second heat generating block having different heat values ​​are arranged in a direction perpendicular to a conveying direction of a recording material; a first temperature detection member that is provided in an area overlapping the first heat generating block when the heater is viewed in a thickness direction of the heater, and detects a temperature of the first heat generating block; a second temperature detection member that is provided in a region overlapping the second heat generating block when the heater is viewed in a thickness direction of the heater and detects a temperature of the second heat generating block; A control unit that controls the supply of power to the plurality of heat generating blocks, the first heat generating block and the second heat generating block are electrically connected to a common power supply path; If a first period is a period from when the supply of power to the common power supply path is started until one of a first detected temperature by the first temperature detection member and a second detected temperature by the second temperature detection member reaches a first temperature which is a control target temperature for a start-up period, and a second period is a period during which the recording material is heated by the heater after one of the first detected temperature and the second detected temperature reaches the first temperature, an image heating device characterized in that, during the second period, the control unit controls the power supplied to the common power supply path using the temperature detection member having the lower detection temperature of the first temperature detection member or the second temperature detection member, so that, during the second period, both of the first detected temperature and the second detected temperature fall within a temperature range between the first temperature and a second temperature which is set to be lower than the first temperature so as not to cause heating defects in an image formed on a recording material.

17. the first temperature is less than an overtemperature threshold; 17. The image heating apparatus according to claim 1, wherein the control unit cuts off the supply of power to the common power supply path when the first detected temperature or the second detected temperature exceeds an overheating threshold.

18. 18. An image heating apparatus according to claim 1, further comprising: a cylindrical film; and a roller that contacts the outer peripheral surface of the film, the heater being disposed in an internal space of the film; the film being sandwiched between the heater and the roller; and an image on a recording material being heated via the film in a nip portion formed between the film and the roller.

19. an image forming section for forming an image on a recording material; a fixing section for fixing the image formed on the recording material to the recording material; In an image forming apparatus having An image forming apparatus, comprising: the fixing unit comprising the image heating device according to claim 1 .

Images