Image heating apparatus and image forming apparatus

Abstract

To provide an image heating device that can perform accurate temperature control.SOLUTION: An image heating device is such that: a plurality of heating elements in a heater include a first heating element group and a second heating element group that are arranged symmetrically with respect to a conveyance reference position of a recording material in a width direction; a control unit supplies power to the first heating element group through a first common circuit, and supplies power to the second heating element group through a second common circuit; a temperature detection unit includes a first temperature detection element 510-11 that detects the temperature of one of the heating elements included in the first heating element group, and a second temperature detection element 510-14 that detects the temperature of one of the heating elements included in the second heating element group. In the image heating device, the first temperature detection element 510-11 is arranged on one side with respect to the conveyance reference position in the width direction, and the second temperature detection element 510-14 is arranged on the other side with respect to the conveyance reference position in the width direction.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a printer or a copier that uses an electrophotographic method. The present invention also relates to an image heating apparatus such as a gloss imparting apparatus that improves the glossiness of a toner image by reheating the toner image fixed to a fixing device or a recording material mounted on the image forming apparatus.

Background Art

[0002] As a fixing device used in an electrophotographic image forming apparatus, a fixing device of a film heating method is known. In the fixing device of the film heating method, the following non-paper-passing part temperature rise is known as a problem. The non-paper-passing part temperature rise is a phenomenon in which, in an image forming apparatus using this fixing device, when printing small-sized paper continuously, the temperature of the area where the paper does not pass gradually rises in the longitudinal direction of the nip part. If the temperature of the non-paper-passing part becomes too high, it will damage each part inside the apparatus such as the heater, the fixing film, and the pressure roller. Further, when printing large-sized paper in a state where the non-paper-passing part temperature rise has occurred, a phenomenon such as toner high-temperature offset may occur in the area corresponding to the non-paper-passing part of the small-sized paper.

[0003] As one method for suppressing this non-paper-passing part temperature rise, a fixing device having a configuration shown in Patent Document 1 has been proposed. That is, it is a fixing device provided with a heater (hereinafter, a divided heater) in which a heating element is arranged by being divided in the longitudinal direction on a substrate. By using this configuration, the heating resistance element on the heater can be divided into a plurality of heating regions (hereinafter, referred to as heating blocks HB) in the longitudinal direction of the heater, and the heat generation distribution of the heater can be switched according to the size of the recording material. By doing so, it is possible to suppress the temperature rise of the non-paper-passing part even when passing small-sized paper.

[0004] Furthermore, Patent Document 1 proposes a configuration in which the circuit supplying power to multiple heating elements is made common. In other words, this configuration uses a common drive to supply power to multiple heating blocks that are installed symmetrically on both sides with respect to the center of the paper. By adopting this configuration, it is possible to achieve miniaturization, cost reduction, and energy saving of the device. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-54071 [Overview of the project] [Problems that the invention aims to solve]

[0006] When using a fixing device with the above-mentioned segmented heater, temperature control is required for each drive circuit. In other words, a temperature sensing element must be installed in at least one of the sets of heat-generating blocks HB that are powered by the same drive, and the power supplied to the drive circuit must be determined using the temperature sensing result of that element, i.e., temperature control must be performed. Here, thermistors are widely used as temperature sensing elements from the standpoint of functionality and cost.

[0007] In this case, the heat-generating elements that make up the heater may have variations in resistance, and in particular, if the resistance distribution varies in the longitudinal direction, the variation in heat distribution may lead to a large difference in fixing performance between the left and right sides. In such cases, depending on the arrangement of the temperature sensing element, it may become difficult to perform temperature control accurately, which may lead to fixing failure or high-temperature offset.

[0008] The objective of the present invention is to provide an image heating device capable of highly accurate temperature control. [Means for solving the problem]

[0009] To solve the above-mentioned problems, the image heating apparatus of the present invention is: A cylindrical film and A heater disposed in the internal space of the film, having a plurality of heating elements arranged in the longitudinal direction of the heater which is perpendicular to the transport direction of the recording material, A pressing member that contacts the outer circumferential surface of the film and forms a nip that clamps the recording material together with the heater through the film, A temperature detection unit for detecting the temperature of the heater, A control unit that controls the power supplied to the plurality of heating elements based on the temperature detected by the temperature detection unit, Equipped with, An image heating device that heats an image formed on a recording material held between the nip by the heat of the heater, The plurality of heating elements are arranged symmetrically in the longitudinal direction with respect to the transport reference position of the recording material. It has two heating elements A first group of heating elements is provided, and the first group of heating elements is positioned symmetrically with respect to the transport reference position at different positions in the longitudinal direction. It has two heating elements A second group of heating elements, The control unit controls the first heating element group. A first common circuit that supplies power, and by controlling a first triac provided in the first common circuit before it branches to the two heating elements of the first heating element group, the power is supplied to the two heating elements of the first heating element group. Power is supplied via the first common circuit to the second heating element group. A second common circuit that supplies power, and by controlling a second triac provided in the second common circuit before it branches to the two heating elements of the second heating element group, the power is supplied to the two heating elements of the second heating element group. Power is supplied via a second common circuit. The temperature detection unit is included in the first heating element group. two One of the heating elements A first temperature sensing element for detecting temperature and the second heating element group included two An image heating device including a second temperature sensing element for detecting the temperature of one of the heating elements, The first temperature sensing element is positioned on one side with respect to the transport reference position in the longitudinal direction. The second temperature sensing element is positioned on the other side of the transport reference position in the longitudinal direction, The control unit controls the first heating element group so that the temperature detected by the first temperature sensing element maintains the control target temperature. two heating elementsPower is supplied to the first common circuit for the second heating element group such that the detected temperature of the second temperature detection element maintains the control target temperature. two heating elements Power is supplied to the second heating element group via the second common circuit, which is characterized. In addition, in order to solve the above problems, the image forming apparatus of the present invention An image forming unit that forms an image on a recording material; A fixing unit that fixes the image formed on the recording material to the recording material; In an image forming apparatus having The fixing unit is the image heating apparatus of the present invention, which is characterized.

Effect of the Invention

[0010] As described above, according to the present invention, the accuracy of temperature control of the image heating apparatus can be improved.

Brief Description of the Drawings

[0011] [Figure 1] Schematic cross-sectional view of the image forming apparatus according to Example 1 [Figure 2] Schematic cross-sectional side view of the fixing apparatus according to Example 1 [Figure 3] Schematic cross-sectional view of the heater according to Example 1 [Figure 4] Electrical circuit diagram according to Example 1 [Figure 5] Schematic cross-sectional view of the thermistor according to Example 1 [Figure 6] Schematic plan view of the heater and thermistor according to Example 1 [Figure 7] Schematic plan view of the heater and thermistor according to the comparative example [Figure 8] Longitudinal distribution diagram of the resistance value and heating element temperature of the heater according to Comparative Example 1 [Figure 9] Longitudinal distribution diagram of the resistance value and heating element temperature of the heater according to Example 1 [Figure 10] Longitudinal temperature distribution diagram of the fixing film surface according to Example 1 [Figure 11] Schematic plan view of the heater according to Example 1 [Figure 12] Schematic plan view of the heater according to Example 1 [Figure 13] Longitudinal distribution diagram of the heater's resistance and heating element temperature according to Example 2. [Figure 14] Longitudinal temperature distribution diagram of the fixing film surface according to Example 2 [Figure 15] Schematic cross-sectional view of the heater according to Example 3 [Modes for carrying out the invention]

[0012] The embodiments for carrying out this invention will be described in detail below with reference to the drawings, based on examples. However, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments should be appropriately modified depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of this invention is not intended to be limited to the following embodiments.

[0013] (Example 1) Figure 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention, which uses electrophotographic recording technology. Examples of image forming apparatuses to which the present invention can be applied include photocopiers and printers that utilize electrophotographic or electrostatic recording methods. Here, we will describe the case in which the present invention is applied to a laser printer that forms an image on a recording material P such as recording paper using an electrophotographic method.

[0014] (Outline configuration of an image forming apparatus) Figure 1 is a schematic cross-sectional view of an example of an image forming apparatus according to Embodiment 1 of the present invention. This image forming apparatus includes an image forming unit A that forms a toner image on a recording material, a recording material feeding unit B that feeds the recording material to the image forming unit A, and a fixing unit (fixing device) C that heat-fixes the toner image on the recording material to the recording material. The image forming unit A has a drum-type electrophotographic photoreceptor (hereinafter referred to as a photosensitive drum) 1 as an image carrier. This photosensitive drum 1 is rotatably supported by the main body M of the image forming apparatus, which constitutes the housing of the image forming apparatus. Around the outer circumferential surface of the photosensitive drum 1, in order along its rotational direction, are a charging roller 2, a laser scanner 3, a developing device 4, a transfer roller 5, and a cleaning device 6. The recording material feeding unit B has a feed roller 11. This feed roller 11 is rotated at a predetermined timing in the direction of the arrow by a transport drive motor (not shown) to feed the recording material P loaded and stored in a cassette 7 to the transport path.

[0015] The image forming apparatus of Example 1 has an image forming unit A, a recording material feeding unit B, a fixing device C, etc., and a control unit (not shown) that controls these. The control unit consists of a CPU and memory such as ROM or RAM, and various programs necessary for image formation are stored in the memory. This control unit receives a print signal from an external device such as a host computer and executes a predetermined image forming control sequence based on the print signal. As a result, the drum motor is driven to rotate, and the photosensitive drum 1 rotates in the direction of the arrow at a predetermined peripheral speed (process speed). The surface of the rotated photosensitive drum 1 is uniformly charged to a predetermined potential with the same polarity as the toner (negative polarity in this case) by the charging roller 2. The laser scanner 3 scans the charged surface of the photosensitive drum 1 with laser light L based on image information and exposes the surface of the photosensitive drum 1. This exposure removes the charge from the exposed area, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

[0016] The developing device 4 has a developing roller 41 and a toner container 42 for storing toner. The toner is rubbed by a component such as a urethane blade (not shown) and charged to a predetermined polarity (negative polarity in Example 1). The developing device 4 applies a negative voltage to the developing roller 41 from a developing voltage power supply (not shown), using the potential difference to deposit toner onto the electrostatic latent image on the surface of the photosensitive drum 1, and develops the electrostatic latent image as a toner image T. The toner image T formed on the surface of the photosensitive drum 1 is transferred to the recording material P by applying a positive voltage, which is the opposite polarity to the toner, to the transfer roller 5, using the potential difference caused by the transfer voltage. A transport drive motor provided in the recording material feeding section B is rotated, and the feed roller 11 feeds the recording material P from the cassette 7 to the transport roller 8. This recording material P is transported by the transport roller 8, passes through the top sensor 9, and is transported to the transfer nip section between the surface of the photosensitive drum 1 and the outer surface of the transfer roller 5. The recording material P onto which the toner image formed on the surface of the photosensitive drum 1 has been transferred is transported along the transport guide 10 to the fixing device C, where the toner image on the recording material P is heated and pressurized to fix it onto the recording material P. The recording material P with the heat-fixed toner image T is then transported along the transport roller 12 and the discharge roller 13 in that order onto the main body M of the device. The material is discharged to the discharge tray 14. After the toner image is transferred to the recording material P, any remaining toner on the surface of the photosensitive drum 1 is removed by the cleaning blade 61 of the cleaning device 6 and stored in the cleaning device 6. By repeating the above operations, printing is performed sequentially. The image forming apparatus of Example 1 can print at a speed of 70 sheets / minute for A4 size. Although details are omitted, the image forming apparatus of Example 1 is equipped with a reverse transport path that enables double-sided image formation, and the recording material P on which an image has been formed on one side is returned to the upstream side of the image forming unit A by a switchback caused by the reverse rotation of the discharge roller 13.

[0017] (Configuration of the fixing device) Figure 2 is a schematic cross-sectional side view of the fixing device C as an image heating device according to Example 1. The fixing device C of Example 1 has as its basic components a heater 1100, a heater holder 29, a metal stay 22, a fixing film 25 as a fixing member, and a pressure roller 26. The heater holder 29 is a holding member that holds (supports) the heater 1100 as a heating element inside the fixing film 25. The fixing device C supports the recording material P in a nip section N between the cylindrical fixing film 25 as a heating rotating body and the pressure roller 26 as a pressure rotating body (pressure member), and heats and fixes the toner image T to the recording material P using the heat of the heater 1100. The nip section N is formed by the heater 1100 and the pressure roller 26 via the fixing film 25. The recording material P is held and conveyed in the nip section N by the rotation of the pressure roller 26 and the driven rotation of the fixing film 25. In this embodiment, the heater 1100 is configured to be in direct contact with the inner surface of the fixing film 25, but a heat transfer member or the like may be interposed between the heater 1100 and the inner surface of the fixing film 25. Among the components of the fixing device C according to this embodiment, the component involved in the formation of the nip portion N constitutes the nip forming portion. The power supply control unit 421, which is connected to a commercial AC power supply, supplies power to the fixing device C based on a signal from the CPU 420.

[0018] (Pressure roller) The pressure roller 26 has an elastic layer 262 on the outer circumference of the core shaft portion 261, and a surface layer 263 on the outer circumference of the elastic layer 262. The outer diameter of the pressure roller 26 is approximately 25 mm. The core shaft portion 261 is made of a metal material such as aluminum or iron, either solid or hollow. In Example 1, solid aluminum is used as the core material. The elastic layer 262 is made of heat-resistant silicone rubber and is made conductive by adding an electrical conductive material such as carbon. The surface layer 263 that comes into contact with the outer surface of the fixing film 25 is a release tube with a thickness of 10 to 80 μm made of fluororesin such as PFA, PTFE, or FEP. Here, PFA is an abbreviation for tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, PTFE is an abbreviation for polytetrafluoroethylene (tetrafluoride), and FEP is an abbreviation for tetrafluoroethylene hexafluoropropylene copolymer (tetrafluoride). The surface layer 263 is preferably made conductive in order to prevent charge buildup associated with paper feeding. In Example 1, the surface layer 263 of the pressure roller 26 was constructed by adding carbon as a conductive material to a 30 μm thick PFA tube.

[0019] (Fixing film) The fixing film 25 has a cylindrical shape with a diameter of 24 mm. The fixing film 25 is flexible and loosely fitted onto the heater holder 29. The layer structure of the fixing film 25 consists of multiple layers, with a base layer 251, an elastic layer 252, and a surface layer 253 provided from the inside, as shown in the cross-sectional configuration within the circle in Figure 2. Generally, low heat capacity heat-resistant resin materials such as polyimide, polyamide-imide, PEEK, and PES are used as the material for the base layer 251. In some cases, metal materials such as SUS are also used. The base layer 251 needs to have a low heat capacity to satisfy quick-start requirements while also satisfying mechanical strength, so it is desirable to use a thickness of 18 μm to 150 μm. In Example 1, the base layer 251 was a cylindrical polyimide base layer with a thickness of 70 μm. The elastic layer 252 is made of an elastic material such as silicone rubber. By providing this elastic layer 252, the toner image T is enclosed. Because heat can be applied uniformly, it becomes possible to obtain high-quality images without unevenness. Since the elastic layer 252 is made of silicone rubber alone, it is used with high thermal conductivity by adding thermally conductive fillers such as alumina, metallic silicon, silicon carbide, and zinc oxide. In high-speed machines like Example 1, it is good to adjust the amount of thermally conductive filler added appropriately to ensure a thermal conductivity of 0.9 W / m·K or higher. In Example 1, alumina and metallic silicon are added as thermally conductive fillers to the rubber material of the elastic layer 252, and its thermal conductivity is set to 1.5 W / m·K. The thickness of the elastic layer 252 is 270 μm. The surface layer 253 is required to be a release layer with high release properties from toner and high abrasion resistance. Fluororesins such as PFA, PTFE, and FEP are used as materials. The layer is formed by a coating layer obtained by firing a resin dispersion, or by a tubular layer. In addition, fluororesins are sometimes used with additives such as carbon or ionic conductive materials to impart conductivity. In Example 1, the surface layer 253 used PFA as the fluororesin, without the addition of conductive materials, and was a 20 μm thick tube layer.

[0020] (Heater holder) The heater 1100 is held in a heater holder 29 made of a heat-resistant resin material such as liquid crystal polymer. The heater holder 29 also has a guide function that guides the rotation of the fixing film 25.

[0021] (heater) Using Figure 3, the heater 1100, a characteristic configuration of this embodiment 1, will be described. The heater 1100 has a ceramic substrate 1105 and a heating resistor (heating element) provided on the substrate 1105 that generates heat when an electric current is passed through it. On the substrate 1105, a glass surface protection layer 1108 is provided on the surface (first surface) that contacts the fixing film 25 on the fixing nip portion N side in order to ensure sliding with the fixing film 25. On the substrate 1105, a glass surface protection layer 1107 is provided on the surface (second surface) opposite to the first surface on the fixing nip portion N side in order to insulate the heating resistor. An electrode E13 is exposed on the second surface, and the heating resistor is electrically connected to the AC power supply when an electrical contact C13 for power supply contacts the electrode.

[0022] Figures 3(a) and 3(b) show the configuration of the heater 1100 in this embodiment. Figure 3(a) is a cross-sectional view of the heater 1100 at the transport reference position X of the recording material P shown in Figure 3(b). Figure 3(b) is a schematic plan view of each layer of the heater 1100. Figure 3(c) is a schematic plan view of the heater holder that holds the heater 1100. In this embodiment, the transport reference position X is set at approximately the center in the width direction perpendicular to the transport direction of the recording material P in the fixing device C, but the setting position is not limited to a specific position.

[0023] The heater 1100 is composed of a substrate 1105, a sliding surface layer provided on the first surface side of the substrate 1105 that contacts the fixing film 25, a back surface layer 1 provided on the second surface side of the substrate 1105 opposite to the first surface side, and a back surface layer 2 covering the back surface layer 1. The heater 1100 has multiple heating blocks along the longitudinal direction on the back surface layer 1, each consisting of a first conductor (conductor A) 1101, a second conductor (conductor B) 1103, and a heating element 1102. In this embodiment, the heater 1100 has a total of five heating blocks HB11 to HB15 formed by multiple heating elements 1102 arranged in the width direction (longitudinal direction of the substrate 1105) perpendicular to the recording material transport direction.

[0024] The heater 1100 shown in Figure 3 is divided into heating blocks HB11 to HB15 symmetrically from the center of the heater 1100 in the longitudinal direction (width direction perpendicular to the recording material transport direction) (symmetrically with respect to the transport reference position X). The division positions of the heating blocks HB correspond to "A5 size", "B5 size", and "A4 size", respectively. That is, heating blocks HB The width of heat block 13 is 150 mm, which is approximately the same as the short side length of A5 size. The width of heat blocks HB12 to HB14 is 182 mm, which is approximately the same as the short side length of B5 size. The width of heat blocks HB11 to HB15 is 210 mm, which is approximately the same as the short side length of A4 size. Of these heat blocks HB, "heat block HB13" is designated as heat group 1, "heat blocks HB12 and HB14" as heat group 2, and "heat blocks HB11 and HB15" as heat group 3. Each heat group is powered by the same drive (common circuit).

[0025] Each heating block's heating element 1102 is divided into two parts with respect to the short-side direction (direction perpendicular to the long-side direction) of the heater 1100: an upstream heating element 1102a and a downstream heating element 1102b. The first conductor 1101 is divided into a conductor 1101a connected to the heating element 1102a and a conductor 1101b connected to the heating element 1102b.

[0026] The heater 1100 is divided into five heating blocks HB11 to HB15. That is, the heating element 1102a is divided into five parts, 1102a-1 to 1102a-5. Similarly, the heating element 1102b is divided into five parts, 1102b-1 to 1102b-5. Furthermore, the second conductor 1103 is also divided into five parts, 1103-1 to 1103-5.

[0027] The back surface layer 2 of the heater 1100 is provided with an insulating surface protection layer 1107 that covers the heating element 1102, the first conductor 1101, and the second conductor 1103. In this embodiment 1, glass is used as the surface protection layer 1107. The surface protection layer 1107 does not cover the electrode portions E11~E15, E18-1, and E18-2, which are in contact with the power supply electrical contacts C11~C15, C18-1, and C18-2. Electrodes E11~E15 are electrodes for supplying power to the heating blocks HB11~HB15 via the second conductors 1103-1~1103-5, respectively. Electrodes E18-1 and E18-2 are electrodes for supplying power to the heating blocks HB11~HB15 via the first conductors 1101a and 1101b.

[0028] In this way, by providing electrodes on the back surface of the heater 1100, it becomes unnecessary to provide conductive patterns on the substrate 1105 for supplying power to the second conductors 1103-1 to 1103-5, thus reducing the width of the substrate 1105 in the shorter direction. As a result, the size increase of the heater 1100 can be suppressed. As shown in Figure 3(b), electrodes E12 to E14 are installed in the region where the heating element is provided in the longitudinal direction of the substrate 1105.

[0029] The heater 1100 of this embodiment 1 can form various heat distributions by independently controlling multiple heat-generating blocks. This makes it possible to set a heat distribution according to the size of the recording material P. Furthermore, the heating element 1102 is made of a material having PTC (Positive Temperature Coefficient) characteristics. This makes it possible to suppress the temperature rise of the non-paper-feeding area as much as possible, even when the edge of the recording material P and the boundary of the heat-generating block do not coincide.

[0030] A sliding layer 1108 is provided on the sliding surface layer of the heater 1100 (the side that contacts the fixing film 25). In this embodiment 1, glass is used as the sliding layer 1108. By providing this sliding layer 1108, smooth sliding between the heater 1100 and the fixing film 25 becomes possible.

[0031] The heater holder 29 will be explained using Figure 3(c). In this embodiment, the heater holder 29 is provided with openings HC11 to HC15, HC18-1, and HC18-2 in order to supply power to electrodes E11 to E15, E18-1, and E18-2 provided on the back surface layer 1 of the heater. Through this opening, power supply units C11-C15, C18-1, and C18-2 supply power to the electrodes. The heater holder 29 is also provided with openings H212-12, H212-13, and H212-15 for installing a thermoswitch 520, and openings H213-12, H213-13, and H213-15 for installing a thermistor 510.

[0032] (Thermistor) Next, the thermistor 510, a characteristic component of this embodiment 1, will be described. The thermistor 510 is an example of a temperature sensing element used in the temperature sensing section of the control configuration of the fixing device C or the image forming apparatus for the purpose of detecting and measuring the temperature of the heater 1100. In particular, the purpose is to perform desired temperature control by reflecting the measurement result in the power supply control of the heater 1100. From the viewpoint of temperature control, it is desirable to install the thermistor 510 in at least one of the heat-generating blocks HB belonging to the heat-generating group that is powered by the same drive.

[0033] The configuration of the thermistor 510 will be explained using Figure 5. As shown in Figure 5, the thermistor 510 consists of a thermistor chip 51, an insulating film 52, an elastic body 53, and a heat-resistant body 54. The thermistor chip 51, which is used for temperature detection, has the characteristic that its resistance value changes with temperature, and is an element that can detect temperature by measuring its resistance value. The insulating film 52, made of polyimide or the like, covers the thermistor chip 51 to ensure its insulation. The elastic body 53 is installed to ensure stable contact between the thermistor chip 51 and the object to be detected by temperature, and ceramic paper or the like is used. The heat-resistant body 54 is made of a heat-resistant material such as liquid crystal polymer (LCP). The thermistor 510 is positioned so that the insulating film 53 is in contact with the surface (surface protective layer 1107) opposite to the surface that forms a nip N between the thermistor 510 and the pressure roller 26 of the heater 1100.

[0034] (Heater power supply control circuit) Figure 4 is a circuit diagram of the control circuit 1400 that controls the heater 1100. Power control (energy supply control) for the heater 1100 is performed by conducting / cutting the power supply to the heater 1100 using triacs 1411 to 1413. Triacs 1411 to 1413 operate according to the FUSER1 to FUSER3 signals from the CPU 420, respectively. The control circuit 1400 for the heater 1100 has a circuit configuration that allows power to be supplied to five heat-generating blocks HB11 to 15 using three triacs 1411 to 1413. Specifically, triac 1411 controls the power supply to heat-generating block HB13 (heat-generating group 1). Triac 1412 controls the power supply to heat-generating blocks HB12 and HB14 (heat-generating group 2), and triac 1413 controls the power supply to heat-generating blocks HB11 and HB15 (heat-generating group 3). In this configuration, heating group 2, which is the first group of heating elements, and heating group 3, which is the second group of heating elements, each have multiple heating blocks HB in a single drive circuit. That is, power is supplied to each heating element included in the group via a single common drive circuit (first common circuit, second common circuit). Note that in Figure 4, the drive circuits for triacs 1411 to 1413 are omitted.

[0035] The zero-cross detection unit 1421 is a circuit that detects the zero-crossing of the AC power supply 1401 and outputs a ZeroX signal to the CPU 420. The ZeroX signal is used as a reference signal for phase control of the triacs 1411 to 1413, etc.

[0036] Relay 1440 is provided as a means of cutting off power to heater 1100 if heater 1100 overheats due to a device malfunction or other factors. In addition, the three thermoswitches 520-11, 520-13, and 520-14 are located on a DC circuit connected to a 24V power supply. The system is configured such that if any one of the three thermoswitches 520-11, 520-13, or 520-14 is opened, the 24V applied to relay 1440 is cut off, relay 1440 opens, and the AC circuit is cut off. In this embodiment, a thermoswitch is described as an example of an overheat protection element, but other elements such as thermal fuses may also be used as elements that detect abnormal heat generation in the heater and cut off the power supply to the heater.

[0037] (Installation locations of thermistor and thermoswitch in Comparative Example 1) Figure 7 is a schematic plan view showing the installation locations of the thermistor 510 and thermoswitch 520 in Comparative Example 1. As shown in Figure 7, in Comparative Example 1, thermistors 510-11, 510-12, and 510-13 are installed on the heating blocks HB11, HB12, and HB13, respectively. In Comparative Example 1, temperature control is performed using these three thermistors 510-11, 510-12, and 510-13. The thermoswitches 520-11, 520-12, and 520-13 are installed on the heating blocks HB11, HB12, and HB13, respectively. In other words, the fixing device of Comparative Example 1 is configured such that thermistors 510-11, 510-12, and 510-13 are positioned on the heat-generating block HB with a bias towards either the left or right side (either the left or right side) relative to the center of the width of the recording material.

[0038] (Issues of Comparative Example 1) In the fixing device of Comparative Example 1 described above, the thermistor is installed on either the left or right side (biased towards one side) relative to the center of the paper. Therefore, if the resistance value of the heater 1100 varies, the left-right difference in fixing performance may become large. As a result, image defects caused by fixing performance, such as poor fixing or hot offset, may occur. As a solution to this problem, for example, product quality could be improved so that the variation in the heater resistance distribution is kept within a predetermined range. However, in order to satisfy the quality requirements of an image forming apparatus, increased costs such as heater selection and management would be unavoidable.

[0039] (Heater resistance variation) Refer to Figures 8(a) and 8(c) to explain the resistance variation of heater heating elements. Due to the manufacturing process, heater heating elements tend to have a uniform resistance distribution in the longitudinal direction. As an example of the resistance distribution of a heater with large resistance unevenness, Figure 8(a) shows the resistance distribution (resistance unevenness) of heating element 1102 of heater A, and Figure 8(c) shows the resistance distribution (resistance unevenness) of heating element 1102 of heater B.

[0040] As shown in Figure 8(a), the resistance of the heating element of heater A changes continuously in the longitudinal direction, with the resistance being higher on the right side of Figure 8(a). In other words, the resistance distribution is sloped (thick solid line extending diagonally in the figure) compared to the uniform resistance distribution in the longitudinal direction (thick solid line extending horizontally in the figure) in the case where there is no resistance unevenness. When power is supplied to heating blocks HB of the same heating group using such a heater, since the heating element is connected in parallel with the electrodes, a lower resistance value of the heating element results in a greater amount of heat generation. Specifically, heating block HB12 generates more heat than heating block HB14, and heating block HB11 generates more heat than heating block HB15.

[0041] As shown in Figure 8(c), the resistance of the heating element in heater B changes continuously in the opposite direction to that of heater A. That is, the resistance on the right side of Figure 8(c) is lower. As a result, when heater B is used, heating block HB12 generates less heat than heating block HB14, and heating block HB11 generates less heat than heating block HB15.

[0042] As described above, the heating element 1102 of the heater 1100 is, for manufacturing reasons, oriented in the longitudinal direction. There is a tendency for it to have a variety of resistance distributions. The heating element 1102 is formed on the ceramic substrate 1105 by techniques such as screen printing. In screen printing, when transferring the heating element 1102 to the ceramic substrate 1105, the amount of heating element 1102 applied is determined by moving a squeegee along the longitudinal direction of the heater 1100. When the heating element 1102 is formed by such screen printing, thickness variations of the heating element 1102 occur in the printing direction of the screen, i.e., in the longitudinal direction of the heater 1100, and as a result, there was a tendency for resistance variations to occur.

[0043] (Temperature control in Comparative Example 1) Figures 8(b) and 8(d) show the temperature control in the fuser of Comparative Example 1 when using heaters A and B described above. Figures 8(b) and 8(d) show the temperature distribution of the heater heating elements when temperature control is performed using thermistors 510-11, 510-12, and 510-13 in the fuser apparatus of Comparative Example shown in Figure 7. Figure 8(b) shows the temperature distribution when temperature control is performed using heater A, and Figure 8(d) shows the temperature distribution when heater B is used. In Comparative Example 1, since temperature control is performed using thermistors 510-11, 510-12, and 510-13, the heater 1100 is temperature-controlled to a predetermined temperature at the installation positions of each thermistor, i.e., P510-11, P510-12, and P510-13.

[0044] When heater A is used, the resistance value of the heating element 1102 in the regions of heating block HB11 and heating block HB12 is lower than the resistance value of heating block HB14 and heating block HB15. As a result, as shown in Figure 8(b), the heating element temperature in heating block HB14 and heating block HB15 becomes lower than in other regions. In other words, when heater A is used, thermistor 510-11 is installed in heating block HB11, so the temperature at the installation location of thermistor 510-11 (P510-11) is controlled to a predetermined temperature. Similarly, thermistor 510-12 is also installed in heating block HB12, so P510-12 is also controlled to a predetermined temperature. On the other hand, in heating blocks HB14 and HB15, the resistance value of the heater heating element is high and the amount of heat generated is small, and since the temperature is controlled by heating blocks HB12 and HB11, the heating element temperature drops even further. As a result, insufficient heat necessary for fixing may be supplied, potentially leading to fixing failure.

[0045] On the other hand, when heater B is used, the resistance value of the heating element 1102 in the regions of heating block HB11 and heating block HB12 is higher than the resistance value of heating block HB14 and heating block HB15. Therefore, when heater B is used, as a result of temperature control performed by thermistors 510-11 and 510-12, the heating element temperature of heating block HB14 and heating block HB15 becomes higher than in other regions, as shown in Figure 8(d). As a result, there is an excess of heat for fixing, which may cause hot offset.

[0046] (Film surface temperature of Comparative Example 1) Next, the longitudinal temperature distribution of the fixing film 25 surface of Comparative Example 1 will be explained using Figure 10. The longitudinal temperature distribution of the fixing film 25 surface is characterized by a gentler temperature change compared to the longitudinal temperature distribution of the heating element 1102. This is because the heat conduction in the longitudinal direction of the heater 1100 and the fixing film 25 is higher than the heat conduction in the thickness direction of the fixing film 25. In other words, when heat is transferred from the heating element 1102 to the heater substrate 1105 and the fixing film 25 in the thickness direction, heat is supplied in the longitudinal direction. Note that the temperature TL shown in Figure 10 is the threshold temperature for fixing failure, and the temperature TH is the threshold temperature for hot offset. Fixing failure occurs when the surface temperature of the fixing film 25 falls below temperature TL, and hot offset occurs when it exceeds temperature TH.

[0047] Figure 10(a) shows the longitudinal temperature distribution on the surface of the fixing film 25 when the temperature is controlled using the fixing device of Comparative Example 1 with heater A, as indicated by the solid line. From Figure 8(b), the longitudinal temperature distribution of the heating element 1102 of Comparative Example 1 shows that the temperature is low in both the heating block HB14 and the heating block HB15. As a result, heat is not supplied longitudinally to the region of the heat-generating block HB15, and the surface temperature of the fixing film 25 becomes low in the region of the heat-generating block HB15. Consequently, the surface temperature of the fixing film 25 falls below the temperature TL, which is the threshold temperature for fixing failure, resulting in fixing failure.

[0048] On the other hand, Figure 10(b) shows a solid line illustrating the longitudinal temperature distribution on the surface of the fixing film 25 when the temperature is controlled using heater B with the fixing device of Comparative Example 1. From Figure 8(d), the longitudinal temperature distribution of the heating element 1102 of Comparative Example 1 shows that the temperature is high in both heating block HB14 and heating block HB15. As a result, the heat supplied in excess to the region of heating block HB15 cannot escape to the other heating blocks HB, and the surface temperature of the fixing film 25 becomes high in the region of heating block HB15. Consequently, the surface temperature of the fixing film 25 exceeds the temperature TH, which is the threshold temperature for hot offset, and hot offset occurs.

[0049] As described above, in the fixing device of Comparative Example 1, if a heater 1100 with a resistance distribution such as heater A or heater B is used, fixing failure or hot offset may occur.

[0050] (Installation locations of thermistor and thermoswitch in Example 1) On the other hand, the fixing device of this embodiment 1 can solve the problems of comparative example 1. Figure 6 shows the installation positions of the thermistor 510 and thermoswitch 520 in embodiment 1. As shown in Figure 6, in embodiment 1, thermistors 510-11, 510-13, and 510-14 are installed on the heating block HB11, heating block HB13, and heating block HB14, respectively. That is, thermistor 510-11 as the second temperature sensing element is positioned to the left (the other side) of the transport reference position X in order to detect the temperature of heating block HB11, which is part of heating group 3 (heating blocks HB11 and HB15), which is part of the second heating element group. Thermistor 510-14 as the first temperature sensing element is positioned to the right (the other side) of the transport reference position X in order to detect the temperature of heating block HB14, which is part of heating group 2 (heating blocks HB12 and HB14), which is part of the first heating element group. In Example 1, temperature control is performed using three thermistors 510-11, 510-13, and 510-14. Thermoswitches 520-11, 520-13, and 520-14 are installed on heating blocks HB11, HB13, and HB14, respectively. Specifically, thermoswitch 520-11, as the second overheat protection element, is positioned in conjunction with heating block HB11, which is included in heating group 3 and corresponds to thermistor 510-11. Similarly, thermoswitch 520-14, as the first overheat protection element, is positioned in conjunction with heating block HB14, which is included in heating group 2 and corresponds to thermistor 510-14.

[0051] (Temperature control in Example 1) Figure 9(a) shows the temperature distribution of the heating element 1102 when thermistor temperature control is performed using the heater 1100 having the resistance distribution shown in Figure 8(a) in this embodiment 1. In this embodiment 1, temperature control is performed using thermistors 510-11, 510-13, and 510-14, so that the temperature is controlled to a predetermined temperature at the installation positions of each thermistor shown in Figure 6, P510-11, P510-13, and P510-14.

[0052] The difference between the heating element 1102 temperature of Comparative Example 1 and the temperature of heating element 1102 is the difference between Figure 8(b) and Figure 9(a), and between Figure 8(d) and Figure 9(b), namely the temperature difference between the regions of heating block HB12 and heating block HB14. In this embodiment 1, temperature control is performed by the thermistor 510-14 installed in heating block HB14, so the temperature of heating block HB14 is controlled to a predetermined temperature. On the other hand, the temperature of the heater heating element 1102 of heating block HB12 is compared to heating block HB14. When heater A is used, the temperature is higher, and when heater B is used, the temperature is lower. In other regions, the temperature is the same in Comparative Example 1 and Example 1.

[0053] (Film surface temperature in Example 1) The longitudinal temperature distribution of the fixing film 25 surface in this embodiment 1 will be explained using Figures 10(a) and 10(b).

[0054] Figure 10(a) shows the longitudinal temperature distribution of the fixing film 25 surface when temperature control is performed using the fixing device of Example 1 with heater A, indicated by a dotted line. As shown in Figure 10(a), the surface temperature of the fixing film 25 in the regions of heating block HB14 and heating block HB15 in Example 1 is higher than the surface temperature of the fixing film 25 in the same region in Comparative Example 1. This is because, since temperature control is performed by the thermistor 510-14 installed in heating block HB14, the temperature of the heating element 1102 of heating block HB14 is higher in Example 1 compared to Comparative Example 1, and that heat also spreads to the region of heating block HB15. As a result, in Example 1, unlike Comparative Example 1, the fixing film surface temperature exceeds TL even in the region of heating block HB15, so fixing failure does not occur. As described above, by using Example 1, the occurrence of fixing failure can be suppressed when heater A is used.

[0055] On the other hand, Figure 10(b) shows a dotted line illustrating the longitudinal temperature distribution on the surface of the fixing film 25 when the fixing device of Example 1 is temperature-controlled using heater B. As shown in Figure 10(b), the surface temperature of the fixing film 25 in the regions of heating blocks HB14 and HB15 in Example 1 is lower than the surface temperature of the fixing film 25 in the same region in Comparative Example 1. This is because the temperature is controlled by the thermistor 510-14 installed in heating block HB14, resulting in a lower temperature for the heating element 1102 of heating block HB14 compared to Comparative Example 1, and the heat from heating block HB15 also circulates to the region of heating block HB14. As a result, in Example 1, unlike Comparative Example 1, the surface temperature of the fixing film is below TH even in the region of heating block HB15, so no hot offset occurs. As described above, in Example 1, the occurrence of hot offset can be suppressed even when heater B is used.

[0056] Based on the above, by using the fixing device of this embodiment 1, it is possible to achieve effects and advantages that could not be obtained in the comparative example.

[0057] In this embodiment 1, the thermistor 510 was installed in three locations: heat-generating blocks HB11, HB13, and HB14. However, this is not limited to the installation of the thermistor 510 in a heat-generating group that includes multiple heat-generating blocks HB, provided that the locations are not adjacent. For example, the thermistor 510 could be installed in heat-generating blocks HB12, 13, and 15.

[0058] Furthermore, in this embodiment 1, we have described an example of a heater 1100 in which heating elements 1102a and 1102b are provided in the direction of transport of the recording material P. However, the shape of the heating elements is not limited as long as the heating element 1100 is divided in the width direction of the recording material P. Also, in this embodiment 1, we have shown a configuration in which electrodes E11~E15 and E18-1~2 are formed on the back surface of the recording material feeding area of ​​the heater 1100, but this is not the only configuration.

[0059] An example of the above configuration is shown in Figure 11. The heater 1100 in Figure 11(a) is divided into five heating elements 1102-1 to 1102-5, and the heating region is divided into five heating blocks HB11 to HB15. The heating block HB is divided into three heating groups for each drive circuit: heating group 1 (heating block HB13), heating group 2 (heating blocks HB12, HB14), and heating group 3 (heating blocks HB11, HB15). Heating group 1 is the heating region that includes the transport reference position X of the recording material P. Heating group 2 The heating element HB has heating blocks HB divided into left and right sides, flanking the transport reference position X of the recording material P, and is installed adjacent to heating group 1 on the side furthest from the transport reference position X of the recording material P. Heating group 3 has heating blocks HB divided into left and right sides, flanking the transport reference position X of the recording material P, and is installed adjacent to heating group 2 on the side furthest from the transport reference position X of the recording material P.

[0060] Here, the heating elements 1102-1 to 1102-5 have a shape that is folded multiple times in the width direction of the heater 1100, as shown in Figure 11(a). Furthermore, the heating elements 1102-1 to 1102-5 receive power from power sources E21 to E24 via conductors 1101a and 1101b-1 to 1101b-5 and generate heat. Thermistors 510 are installed on the heater 1101 at the positions shown in Figure 11(b). That is, thermistor 510-11 is installed in the region of heating block HB11, thermistor 510-13 is installed in heating block HB13, and thermistor 510-14 is installed in heating block HB14. By doing so, the effects of this embodiment can be achieved. Note that in this case as well, it is also possible to install thermistors on heating blocks HB12, HB13, and HB15.

[0061] Furthermore, although this embodiment describes a case where the heat generation group is divided into three parts, similar effects can be achieved in fixing devices with more divided heat generation areas. An example is shown in Figure 12. As shown in Figure 12, heat generation group (n) consists of heat generation blocks HB(n) and HB(n)' supplied with power by the same drive, and heat generation blocks HB(n) and HB(n)' are arranged on either side of the transport reference position X of the recording material P. Heat generation group (n+1) consists of heat generation blocks HB(n+1) and HB(n+1)' supplied with power by the same drive, and heat generation blocks HB(n+1) and HB(n+1)' are arranged on either side of the transport reference position X of the recording material P. Heat generation group (n+1) is installed adjacent to heat generation group (n) in a direction away from the transport reference position X of the recording material P. In this case, the thermistor 510 was installed in the position shown in Figure 12. Specifically, thermistor 510-(n) was installed in heating block HB(n), and thermistor 510-(n+1) was installed in heating block HB(n+1)'. By doing so, even in a fixing device using a more multi-segmented heater 1100, good fixing performance can be satisfied regardless of longitudinal variations in heater resistance.

[0062] Furthermore, in this embodiment 1, the insulating film 53 of the thermistor 510 was positioned to contact the heater 1100, but the position of the thermistor chip 51 is not particularly limited as long as it can detect the temperature of the area of ​​the heat-generating block HB.

[0063] Furthermore, in this embodiment 1, the thermistor 510 and the thermoswitch 520 are installed in the same heat-generating block HB, but from the viewpoint of space saving, it is also possible to install them in different heat-generating blocks HB of the same drive. For example, the thermistor 510 may be installed in heat-generating blocks HB11 and HB14, and the thermoswitch 520 may be installed in heat-generating blocks HB12 and HB15. By installing them in this way, the thermistor 510 and the thermoswitch 520 can be installed efficiently. As a result, the heater 1100 can be made smaller and its cost can be reduced.

[0064] (Example 2) This embodiment 2 describes a fixing device suitable for cases where the heater 1100 has a large longitudinal resistance distribution and has means for detecting that resistance distribution. The only differences between embodiment 2 and embodiment 1 are the resistance distribution of the heater 1100, the means for detecting the resistance distribution, and the control method thereof. Other configurations are the same as in embodiment 1, so a further explanation is omitted. Matters in embodiment 2 that are not specifically described here are the same as in embodiment 1.

[0065] (Heater resistance variation in Example 2) Figures 13(a) and 13(c) show the resistance unevenness of the heating elements 1102 of "Heater C" and "Heater D," which are representative heaters 1100 with large resistance unevenness used in Example 2. Figure 13(a) shows the resistance unevenness of "Heater C," and Figure 13(c) shows the resistance unevenness of "Heater D." Heater C has higher resistance values ​​towards the right, and Heater D has lower resistance values ​​towards the right, with larger resistance distributions than Heater A and Heater B in Example 1, respectively.

[0066] Next, the means for detecting heater resistance in Example 2 will be described. In the fixing device of Example 2, the resistance value distribution of the heating element 1102, which was measured in advance during the manufacturing of the heater 1100, is stored in a storage means such as a fixing memory.

[0067] In Example 2, the means for detecting the resistance distribution (acquisition unit) is shown as a method for pre-measuring the resistance distribution of the heating element 1102, but other means can also be used. For example, it is also possible to use means such as comparing the thermistor temperature at startup or comparing the power input during temperature control.

[0068] The fixing control of Example 2 will be explained with reference to Figures 13(b) and 13(d). In the fixing apparatus of Example 2, the temperature control means when heater C is used is shown in Figure 13(b), and the temperature control means when heater D is used is shown in Figure 13(d).

[0069] When heater C is used, as shown in Figure 13(b), the temperature control temperature of thermistor 510-11 is set higher than that of thermistor 510-13, and the temperature control temperature of thermistor 510-14 is set lower than that of thermistor 510-13. It is desirable to set the temperature control temperature so that the temperature difference between heating block HB11 and heating block HB12, and the temperature difference between heating block HB14 and heating block HB15, which can be expected from the resistance distribution of the heating element 1102, does not exceed a predetermined value.

[0070] In this embodiment 2, the temperature control temperatures for thermistors 510-11 and 510-14 were determined by the following procedure. Using heater resistance distribution data stored in the fixing memory, a predicted value for the heater heating element 1102 temperature is calculated when the same power is applied to all heating groups 1 to 3 (shown by a dotted line in Figure 13(b)). The predicted value T11a of the heating element 1102 temperature of P510-11 and the temperature control temperature T13 of P510-13 are averaged to calculate T11b. At this time, the difference between the predicted value T11a and T11b is the same as the difference between T11b and the temperature control temperature T13. Then, T11b is set as the temperature control temperature (control target temperature) for thermistor 510-11. Similarly, for thermistor 510-14, the predicted temperature T14a of the heating element 1102 of P510-14 is averaged with the temperature-controlled temperature T13 of P510-13 to calculate T14b. At this time, the difference between the predicted value T14a and T14b is the same as the difference between T14b and the temperature-controlled temperature T13. Then, this temperature T14b is set as the temperature-controlled temperature (control target temperature) of thermistor 510-14.

[0071] On the other hand, when using heater D, the temperature control temperatures for thermistors 510-11 and 510-14 were determined using the same procedure as when using heater C. When using heater D, as shown in Figure 13(d), the temperature control temperature for thermistor 510-11 was set lower than that for thermistor 510-13, and the temperature control temperature for thermistor 510-14 was set higher than that for thermistor 510-13.

[0072] The longitudinal temperature distribution of the fixing film 25 surface in this embodiment 2 will be explained using Figures 14(a) and 14(b). The longitudinal temperature distribution of the fixing film 25 surface when temperature control is performed using the fixing device of embodiment 2 with heater C is shown by a dotted line in Figure 14(a). As shown in Figure 14(a), in this embodiment 2, the surface temperature of the fixing film is above TL throughout the entire longitudinal region. No fixing failures occur. Furthermore, the longitudinal temperature distribution of the fixing film 25 surface when temperature control is performed using the fixing device of Example 2 with heater D is shown by a dotted line in Figure 14(b). As shown in Figure 14(b), in Example 2, the surface temperature of the fixing film is below TH throughout the entire longitudinal region, and no hot offset occurs.

[0073] As described above, by using the fixing device of this embodiment 2, variations in the longitudinal temperature distribution of the fixing film 25 can be reduced. This suppresses the occurrence of fixing failures and hot offsets. Furthermore, the temperature difference between the heating blocks HB, specifically between heating block HB11 and heating block HB12, and between heating block HB14 and heating block HB15, can be reduced. This suppresses the occurrence of image defects caused by temperature differences between heating blocks HB, such as uneven gloss.

[0074] (Example 3) The fixing device of Example 3 is characterized in that the thermistor 510 for temperature detection is a printed thermistor formed on the heater substrate 1105, and multiple printed thermistors are formed on a single heat-generating block HB. The other configurations are the same as those of Example 1, so a further explanation is omitted. Matters not specifically described here in Example 3 are the same as in Examples 1 and 2.

[0075] The placement of the thermistor in Example 3 will be explained using Figure 15(b). The heater 1100 in Example 3 has a sliding surface layer 1 on the sliding surface side that contacts the fixing film 25, and a sliding surface layer 2 that covers the sliding surface layer 1. Multiple printed thermistors are formed on the sliding surface layer 1 of the heater 1100 to detect the temperature of each heating block HB11 to HB15. The multiple thermistors are shown in Figure 15(b) as T11-1C, T11-3C, T11-1E to T11-3E, T12-4C, and T12-3E to T12-5E, respectively. The material of the thermistor can be any material with a large positive or negative TCR (Temperature Coefficient of Resistance). In this embodiment 3, a thermistor was constructed by thinly printing a material having NTC (Negative Temperature Coefficient) characteristics, where the TCR is negative, onto the substrate 1105.

[0076] Next, the thermistor placement for each heat-generating block HB will be described. In this embodiment 3, as shown in Figure 15(b), two or more thermistors are placed in all of the heat-generating blocks HB11 to HB15. For example, two thermistors, T11-1C and T11-1E, are installed in heat-generating block HB11, and the temperature of each thermistor is detected by conductive patterns ET11-1C and ET11-1E for resistance detection and a common conductive pattern EG11. Thermistor T11-1C is a thermistor for detecting the temperature of the central region of heat-generating block HB11 and is located approximately in the center of heat-generating block HB11 in the width direction of the recording material P. Thermistor T11-2E is an end thermistor for detecting the temperature of the end region of heat-generating block HB12 and is located at the position furthest from the transport reference X within the region of heat-generating block HB11 in the width direction of the recording material P. Thus, thermistors T11-1C, T11-3C, and T12-4C are positioned for the heating blocks HB11, HB13, and HB14 to detect the temperature in the central region. In addition, end thermistors T11-1E to T11-3E and T12-3E to T12-5E are positioned for each heating block HB11 to HB15 to detect the temperature in the end region.

[0077] In this embodiment 3, one temperature-controlled thermistor is set for each heat-generating group to control the temperature of the heat-generating block HB belonging to each heat-generating group. Heat-generating group 1 uses thermistor T11-3C, heat-generating group 2 uses thermistor T12-4C, and heat-generating group 3 uses thermistor T11-1C is used as a temperature control thermistor. In this embodiment 3, the temperature control thermistors that control the temperature of the heat-generating blocks belonging to each heat-generating group are arranged separately to the left and right of the transport reference of the recording material P in adjacent heat-generating groups. This makes it possible to suppress the occurrence of fixing failures and hot offsets even if there are variations in the resistance values ​​of the heater 1100.

[0078] In this embodiment 3, the temperature control thermistors only need to be positioned on either side of the transport reference point in adjacent heat-generating groups, and this does not apply to thermistors intended for temperature detection. For example, the detection result of thermistor T12-5E installed in the area of ​​heat-generating block HB15 can be used to perform an auxiliary role, such as changing the temperature control temperature. [Explanation of Symbols]

[0079] C... Fixing device, 1100... Heater, 1102... Heating element, 29... Heater holder, 510... Thermistor, 520... Thermoswitch, 25... Fixing film, 26... Pressure roller

Claims

1. A cylindrical film and A heater disposed in the internal space of the film, having a plurality of heating elements arranged in the longitudinal direction of the heater which is perpendicular to the transport direction of the recording material, A pressing member that contacts the outer circumferential surface of the film and forms a nip that clamps the recording material together with the heater through the film, A temperature detection unit for detecting the temperature of the heater, A control unit that controls the power supplied to the plurality of heating elements based on the temperature detected by the temperature detection unit, Equipped with, An image heating device that heats an image formed on a recording material held between the nip by the heat of the heater, The plurality of heating elements include a first group of heating elements having two heating elements arranged symmetrically with respect to the transport reference position of the recording material in the longitudinal direction, and a second group of heating elements having two heating elements arranged symmetrically with respect to the transport reference position at different positions in the longitudinal direction from the first group of heating elements. The control unit supplies power to the two heating elements of the first heating element group via the first common circuit by controlling a first triac provided in the first common circuit that supplies power to the first heating element group before it branches off to the two heating elements of the first heating element group, and supplies power to the two heating elements of the second heating element group via the second common circuit by controlling a second triac provided in the second common circuit that supplies power to the second heating element group before it branches off to the two heating elements of the second heating element group. In an image heating device, the temperature detection unit includes a first temperature detection element for detecting the temperature of one of the two heating elements included in the first heating element group, and a second temperature detection element for detecting the temperature of one of the two heating elements included in the second heating element group, The first temperature sensing element is positioned on one side with respect to the transport reference position in the longitudinal direction. The second temperature sensing element is positioned on the other side of the transport reference position in the longitudinal direction, The image heating device is characterized in that the control unit supplies power to two heating elements of the first heating element group via the first common circuit so that the temperature detected by the first temperature sensing element maintains the control target temperature, and supplies power to two heating elements of the second heating element group via the second common circuit so that the temperature detected by the second temperature sensing element maintains the control target temperature.

2. The image heating apparatus according to claim 1, characterized in that the first heating element group and the second heating element group are adjacent in the longitudinal direction.

3. The image heating device according to claim 1, characterized in that the first temperature sensing element and the second temperature sensing element are arranged to contact the surface of the heater opposite to the surface that forms the nip between it and the pressurizing member.

4. The image heating apparatus according to any one of claims 1 to 3, characterized in that the first temperature sensing element and the second temperature sensing element are thermistors.

5. The heater includes a substrate on which the plurality of heating elements are formed. The image heating apparatus according to any one of claims 1 to 3, characterized in that the first temperature sensing element and the second temperature sensing element are printed thermistors formed on the substrate.

6. The apparatus further comprises an acquisition unit for acquiring the resistance distribution of the heater in the longitudinal direction, The image heating apparatus according to any one of claims 1 to 5, characterized in that the control unit controls the power supplied to the plurality of heating elements based on the resistance distribution acquired by the acquisition unit and the temperature detected by the temperature detection unit.

7. The image heating apparatus according to claim 6, characterized in that the control unit controls the power supplied to the plurality of heating elements so that the temperature difference between the first heating element group and the second heating element group does not exceed a predetermined value.

8. The aforementioned device further comprises a plurality of protective elements, The aforementioned multiple protective elements are A first protective element is positioned corresponding to one of the heating elements included in the first group of heating elements, A second protective element is positioned corresponding to one of the heating elements included in the second group of heating elements, The image heating apparatus according to any one of claims 1 to 7, characterized by including the following:

9. The first protective element is positioned in accordance with the heating element included in the first heating element group, and the heating element on which the first temperature sensing element is positioned. The image heating device according to claim 8, characterized in that the second protective element is arranged in correspondence with a heating element among the heating elements included in the second heating element group, on which the second temperature sensing element is arranged.

10. The first protective element is positioned in relation to a heating element that is different from the heating element in the first heating element group to which the first temperature sensing element is positioned. The second protective element is positioned to correspond to a heating element among the heating elements included in the second heating element group, which is different from the heating element to which the second temperature sensing element is positioned. The image heating device according to claim 8, characterized by its features.

11. The first temperature sensing element is arranged to detect the temperature of the central region in the longitudinal direction of one of the heating elements included in the first heating element group, The image heating device according to any one of claims 1 to 10, characterized in that the second temperature sensing element is arranged to detect the temperature of the central region in the longitudinal direction of one of the heating elements included in the second heating element group.

12. The image heating apparatus according to claim 11, wherein the temperature sensing unit further includes a temperature sensing element for detecting the temperature of the end region in the longitudinal direction of each of the plurality of heating elements.

13. An image forming unit that forms an image on the recording material, A fixing unit that fixes the image formed on the recording material to the recording material, In an image forming apparatus having, An image forming apparatus characterized in that the fixing unit is an image heating device according to any one of claims 1 to 12.

Images