Fixing device and image forming apparatus

Abstract

To prevent deformation of a heater substrate caused by a positioning part of a soaking member.SOLUTION: A fixing device comprises: a heater 54 that has an elongated heater substrate 54a, and a plurality of heating elements 54b arranged on the heater substrate 54a; an aluminum plate 60 that averages the temperature of the heater substrate 54a; and a heater holder 52 that holds the heater 54 and the aluminum plate 60. In a thickness direction of the heater substrate 54a, the aluminum plate 60 is arranged between the heater 54 and the heater holder 52. The aluminum plate 60 has a positioning part 60a that determines the position in a longitudinal direction of the aluminum plate 60 relative to the heater holder 52. The positioning part 60a is located, in the longitudinal direction, at a position overlapping a heating element b1 of the plurality of heating elements 54b, and a position outside an area of a heating element 54b2 of the plurality of heating elements 54b.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus equipped with the fixing device. [Background technology]

[0002] Conventionally, image forming apparatuses include a fixing device that heats and pressurizes a toner image transferred onto a recording material to fix the toner image to the recording material. Some fixing devices include multiple heating elements of different lengths to heat the recording material according to the width of the recording material. For example, Patent Document 1 discloses the following configuration of a fixing device that includes multiple heating elements of different longitudinal lengths. In the fixing device of Patent Document 1, to suppress thermal deformation of the heater substrate, the heating elements that are long in the longitudinal direction are arranged symmetrically around the center of the heater substrate near both ends in the lateral direction, and the heating elements that are short in the longitudinal direction are arranged between the long heating elements in the longitudinal direction. Furthermore, Patent Document 2, for example, proposes a configuration in which a highly thermally conductive heat equalizing member is arranged on the back surface of the heater substrate to reduce temperature unevenness of the heater substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-115189 [Patent Document 2] Patent No. 6242181 Summary of the Invention [Problem to be solved by the invention]

[0004] In a configuration in which a heat equalizing member such as an aluminum plate is placed in contact with a heater substrate to reduce temperature unevenness in the heater, which is a heating element, a positioning portion may be provided on the heat equalizing member to secure the heat equalizing member to a heater holder that holds the heater. The positioning portion is formed, for example, by bending a portion of the aluminum plate used as the heat equalizing member, and the position of the heat equalizing member is fixed by fitting the bent portion into a recessed portion formed in the heater holder.

[0005] In this case, the bent portion, which is the positioning portion, has a larger volume of the temperature equalizing member than the portion not bent, and therefore a larger heat capacity. As a result, the region of the heater substrate facing the positioning portion of the temperature equalizing member is less likely to increase in temperature than other regions without positioning portions. The resulting regions of different temperatures on the heater substrate create a local temperature gradient, which may cause deformation of the heater substrate.

[0006] The present invention has been made under these circumstances, and has an object to suppress deformation of the heater substrate due to the positioning portion of the heat equalizing member. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0008] (1) A fixing device for fixing an unfixed toner image on a recording material to the recording material, comprising: a heater having an elongated substrate and a plurality of heating elements arranged on the substrate; a heat equalizing member for equalizing the temperature of the substrate; and a holder for holding the heater and the heat equalizing member, wherein the heat equalizing member is arranged between the heater and the holder in the thickness direction of the substrate, and the heat equalizing member has a positioning part for determining the longitudinal position of the heat equalizing member relative to the holder, and the positioning part is located in a position overlapping with a first heating element of the plurality of heating elements in the longitudinal direction, and outside the area of ​​a second heating element of the plurality of heating elements.

[0009] (2) An image forming apparatus comprising: an image forming means for forming an unfixed toner image on a recording material; and the fixing device according to (1) above for fixing the unfixed toner image on the recording material. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress deformation of the heater substrate due to the positioning portion of the heat equalizing member. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing the configuration of an image forming apparatus according to first to third embodiments; [Figure 2] FIG. 1 is a block diagram showing the configuration of a control unit of an image forming apparatus according to first to third embodiments. [Figure 3] Schematic cross-sectional view illustrating the configuration of the fixing device according to Examples 1 and 2. [Figure 4] Schematic diagram illustrating the configuration of the heater in Examples 1 and 2. [Figure 5] Circuit diagram of the power control circuit of the first embodiment [Figure 6] Schematic diagram illustrating a current path to a heating element in Example 1. [Figure 7] Schematic diagram showing the configuration of a heat equalizing member according to Example 1 [Figure 8] FIG. 1 is a diagram illustrating the positional relationship between the positioning portion of the heat equalizing member and the heating element in the first embodiment. [Figure 9] Circuit diagram of a power control circuit according to a second embodiment [Figure 10] FIG. 10 is a diagram illustrating the configuration of a heating element according to a second embodiment. [Figure 11] Schematic diagram showing the configuration of a heat equalizing member according to Example 2 [Figure 12] FIG. 10 is a diagram illustrating the positional relationship between the positioning portion of the heat equalizing member and the heating element in the second embodiment. [Figure 13] Circuit diagram of a power control circuit according to a third embodiment DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following embodiments, the term "passing" refers to passing a recording material through a fixing nip portion of a fixing device. [Example]

[0013] [Overall configuration of image forming device] FIG. 1 is a cross-sectional view showing the configuration of an in-line color image forming apparatus, which is an image forming apparatus equipped with the fixing device of Example 1. The configuration of the electrophotographic color image forming apparatus will be described using FIG. 1. The first station is a station for forming a yellow (Y) toner image, and the second station is a station for forming a magenta (M) toner image. The third station is a station for forming a cyan (C) toner image, and the fourth station is a station for forming a black (K) toner image.

[0014] In the first station, the photosensitive drum 1a, which serves as an image carrier, is an OPC photosensitive drum. The photosensitive drum 1a is a metal cylinder with multiple layers of functional organic materials laminated on it, including a carrier generation layer that generates charge upon photosensitivity and a charge transport layer that transports the generated charge. The outermost layer has low electrical conductivity and is substantially insulated. The charging roller 2a, which serves as a charging means, contacts the photosensitive drum 1a and rotates in accordance with the rotation of the photosensitive drum 1a, uniformly charging the surface of the photosensitive drum 1a. A voltage consisting of a DC voltage or a superimposed AC voltage is applied to the charging roller 2a, generating discharges in the small air gaps upstream and downstream of the rotational direction of the photosensitive drum 1a from the nip between the charging roller 2a and the surface of the photosensitive drum 1a. This charges the photosensitive drum 1a. The cleaning unit 3a cleans toner remaining on the photosensitive drum 1a after the primary transfer described below. The developing unit 8a, which is the developing means, stores non-magnetic single-component toner 5a and has a developing roller 4a and a developer application blade 7a. The photosensitive drum 1a, charging roller 2a, cleaning unit 3a, and developing unit 8a are housed in an integrated process cartridge 9a (image forming section) that is detachably attached to the image forming apparatus.

[0015] The exposure device 11a, which serves as an exposure means, is composed of a scanner unit or LED (light-emitting diode) array that reflects laser light from a rotating polygon mirror and scans the photosensitive drum 1a. The scanning beam 12a, modulated based on an image signal, is irradiated onto the photosensitive drum 1a. The charging roller 2a is connected to a charging high-voltage power supply 20a, which supplies voltage to the charging roller 2a. The developing roller 4a is connected to a developing high-voltage power supply 21a, which supplies voltage to the developing roller 4a. The primary transfer roller 10a is connected to a primary transfer high-voltage power supply 22a, which supplies voltage to the primary transfer roller 10a. The above describes the configuration of the first station, and the second, third, and fourth stations have similar configurations. In the second, third, and fourth stations, components having the same functions as those in the first station are designated by the same reference numerals, with the suffixes b, c, and d added to the reference numerals for each station. In the following description, the suffixes a, b, c, and d will be omitted except when describing a specific station.

[0016] The intermediate transfer belt 13 is supported by three rollers that serve as tensioning members: a secondary transfer opposing roller 15, a tension roller 14, and an auxiliary roller 19. Only the tension roller 14 is subjected to a force in the direction of tensioning the intermediate transfer belt 13 by a spring (not shown), thereby maintaining an appropriate tension on the intermediate transfer belt 13. The secondary transfer opposing roller 15 rotates by receiving rotational drive from a main motor 99 (see FIG. 2), causing the intermediate transfer belt 13 wound around its periphery to rotate. The intermediate transfer belt 13 moves at approximately the same speed in the direction of the arrow (e.g., clockwise in FIG. 1) as the photosensitive drums 1a-1d (e.g., counterclockwise in FIG. 1). The primary transfer roller 10 is positioned opposite the photosensitive drum 1 across the intermediate transfer belt 13 and rotates in response to the movement of the intermediate transfer belt 13. The position where the photosensitive drum 1 and the primary transfer roller 10 abut across the intermediate transfer belt 13 is called the primary transfer position. The auxiliary roller 19, tension roller 14, and secondary transfer opposing roller 15 are electrically grounded. Note that the primary transfer rollers 10b to 10d of the second to fourth stations have the same configuration as the primary transfer roller 10a of the first station, so a description thereof will be omitted.

[0017] Next, the image forming operation of the image forming apparatus shown in FIG. 1 will be described. When the image forming apparatus receives a print command while in standby mode, it starts the image forming operation. The photosensitive drum 1, intermediate transfer belt 13, etc. begin to rotate in the direction of the arrow in the figure at a predetermined process speed driven by a main motor 99 (see FIG. 2). The photosensitive drum 1a is uniformly charged by a charging roller 2a to which a charging voltage is applied from a charging high-voltage power supply 20a. Then, an electrostatic latent image corresponding to the image information is formed by a scanning beam 12a irradiated from an exposure device 11a. The toner 5a in the development unit 8a is negatively charged by a developer application blade 7a and applied to the development roller 4a. A predetermined development voltage is then applied to the development roller 4a from a development high-voltage power supply 21a. When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the development roller 4a, the electrostatic latent image is visualized by the adhesion of negative toner, and a toner image of a first color (e.g., Y (yellow)) is formed on the photosensitive drum 1a. The stations (process cartridges 9b-9d) for the other colors M (magenta), C (cyan), and K (black) operate in the same way. With a delay in the write start signal from the controller (not shown), scanning beams 12a-12d from exposure devices 11a-11d form electrostatic latent images on the photosensitive drums 1a-1d, respectively, at timings according to the distance between the primary transfer positions of each color. A high DC voltage of opposite polarity to the toner is applied to each of the primary transfer rollers 10a-10d from primary transfer high-voltage power supplies 22a-22d. As a result, the toner images on the photosensitive drums 1a-1d are transferred in sequence to the intermediate transfer belt 13 (hereinafter referred to as primary transfer), forming a multi-toner image on the intermediate transfer belt 13.

[0018] Thereafter, in synchronization with the formation of the toner image, paper P, which is a recording material loaded in cassette 16 (paper supply unit), is fed to a conveyance path Y by a feed roller 17, which is driven to rotate by a paper feed solenoid (not shown). The fed paper P is conveyed to a registration roller (hereinafter referred to as a registration roller) 18 by a conveyance roller (not shown). The paper P is conveyed by the registration roller 18 to a transfer nip, which is a contact portion between the intermediate transfer belt 13 and a secondary transfer roller 25, in synchronization with the toner image on the intermediate transfer belt 13. A voltage of opposite polarity to that of the toner is applied to the secondary transfer roller 25 by a secondary transfer high-voltage power supply 26, and the four-color multi-toner image carried on the intermediate transfer belt 13 is transferred collectively onto the paper P (recording material) (hereinafter referred to as a secondary transfer). Meanwhile, after the secondary transfer is completed, a cleaning unit 27 cleans off any toner remaining on the intermediate transfer belt 13. After the secondary transfer is completed, the paper P is transported to fixing device 50, which is a fixing means, and the paper P with the fixed toner image is discharged to discharge tray 30 as an image-formed product (print, copy). It takes, for example, about 9 seconds from the start of the image forming operation until the paper P reaches fixing nip N (see FIG. 3), which will be described later, and it takes, for example, about 12 seconds until the paper P is discharged. The fixing film 51, heater holder 52, pressure roller 53, and heater 54 of fixing device 50 will be described later.

[0019] A printing mode in which images are continuously printed on multiple sheets of paper P is hereinafter referred to as continuous printing or continuous job. In continuous printing, the distance between the rear end of a sheet of paper P (hereinafter referred to as a leading sheet) on which printing is performed first and the front end of a subsequent sheet of paper P (hereinafter referred to as a following sheet) on which printing is performed after the leading sheet is referred to as the paper gap. In this embodiment, in continuous printing of A4-sized sheets of paper P, the toner image on the intermediate transfer belt 13 and the sheets of paper P are transported synchronously so that the distance between the sheets is, for example, 30 mm, and printing is performed. The image forming apparatus of this embodiment is a center-based image forming apparatus that performs printing by aligning the center positions of each component and the sheets of paper P in a direction perpendicular to the transport direction (the longitudinal direction, described below). Therefore, the center positions of each sheet of paper P are aligned whether the printing operation is for a sheet of paper P that is long in the direction perpendicular to the transport direction or a sheet of paper P that is short in the direction perpendicular to the transport direction.

[0020] [Image forming device control block] Figure 2 is a block diagram showing the configuration of the control unit of the image forming apparatus, and the printing operation of the image forming apparatus will be described with reference to Figure 2. PC 110, which is a host computer, sends a print command including image data of the print image and print information to a video controller 91 inside the image forming apparatus.

[0021] The video controller 91 converts image data received from the PC 110 into exposure data and transfers it to an exposure control device 93 in the engine controller 92, while also sending a print command to the CPU 94 in the engine controller 92. The exposure control device 93 is controlled by the CPU 94, and controls the exposure device 11, which turns the laser light on and off according to the exposure data. The size of the exposure data is determined by the image size. When the CPU 94, which is a control means, receives a print command from the video controller 91, it starts the image formation operation.

[0022] The engine controller 92 is equipped with a CPU 94, a memory 95, and the like. The CPU 94 operates according to a program stored in advance in the memory 95. The CPU 94 also has a timer for measuring time, and the memory 95 stores various information for controlling the fixing device 50, which will be described later. The high-voltage power supply 96 is composed of the charging high-voltage power supply 20, the developing high-voltage power supply 21, the primary transfer high-voltage power supply 22, and the secondary transfer high-voltage power supply 26. The power control unit 97 also has a bidirectional thyristor (hereinafter referred to as a triac) 56, which serves as a supply control unit. The power control unit 97 also has a heating element switch 57, which is a switching unit that switches the heating element by switching the power supply path through which power is supplied. The power control unit 97 selects the heating element to which power is supplied in the fixing device 50 and determines the amount of power to be supplied. In this embodiment, the heating element switch 57 is, for example, an a-contact relay.

[0023] The drive device 98 is composed of a main motor 99, a fixing motor 100, etc. The sensor 101 is composed of a fixing temperature sensor 59, which is a temperature detection means for detecting the temperature of the fixing device 50, and a paper sensor 102, which has a flag and detects the presence or absence of paper P. The detection result of the sensor 101 is sent to the CPU 94. The CPU 94 acquires the detection result of the sensor 101 and controls the exposure device 11, the high-voltage power supply 96, the power control unit 97, and the drive device 98 based on the detection result. As a result, the CPU 94 performs the formation of an electrostatic latent image, the transfer of the developed toner image to paper P, the fixing of the transferred toner image to paper P, etc., and controls the image forming process in which image data received from the PC 110 is printed as a toner image on paper P. Note that the image forming apparatus to which the present invention is applied is not limited to the image forming apparatus configured as described in FIG. 1, but may be any image forming apparatus capable of printing on paper P of different widths and equipped with a fixing device 50 having a heater 54, which will be described later.

[0024] [Configuration of fixing device] Next, the configuration of the fixing device 50 that controls the heating device (heater) that heats the toner image on the paper P with a heat generating element will be described with reference to Figure 3. Here, the "longitudinal direction" refers to the direction of the rotation axis of the pressure roller 53, which is approximately perpendicular to the transport direction of the paper P, which will be described later. The length of the paper P in the direction (longitudinal direction) that is approximately perpendicular to the transport direction of the paper P is called the paper width.

[0025] FIG. 3 is a cross-sectional view illustrating the configuration of the fixing device 50. In the fixing device 50, a sheet of paper P carrying an unfixed toner image T is transported from the left side of the figure in the direction of the arrow toward a fixing nip N formed by a fixing film 51 (hereinafter referred to as film 51) and a pressure roller 53 in contact with each other. In the fixing nip N, the fixing film 51 is sandwiched between the pressure roller 53 and a heater 54. The sheet of paper P is heated while being transported from the left side to the right side of the figure in the fixing nip N, thereby fixing the toner image T to the sheet of paper P. The fixing device 50 includes a cylindrical film 51, a heater holder 52 that holds the film 51, a pressure roller 53 that forms the fixing nip N together with the film 51, and a heater 54 (heater unit) that heats the sheet of paper P. The fixing device 50 also includes an aluminum plate 60 that serves as a heat equalizer and is disposed between the heater 54 and the heater holder 52.

[0026] The film 51 is a fixing film that serves as a heating rotor. The film 51 uses, for example, polyimide as a base layer, and an elastic layer made of silicone rubber and a release layer made of PFA are formed on the base layer. The inner diameter of the film 51 is 18 mm, and the outer periphery of the film 51 is approximately 58 mm. Grease is applied to the inner surface of the film 51 to reduce the friction generated between the heater holder 52 and heater 54 and the film 51 as the film 51 rotates.

[0027] The heater holder 52 guides the film 51 from the inside and forms a fixing nip N between the film 51 and the pressure roller 53. The heater holder 52 is a rigid, heat-resistant, and heat-insulating member made of a liquid crystal polymer or the like. The film 51 is fitted onto the heater holder 52. The pressure roller 53 is a roller serving as a pressure rotating body and is composed of a core metal 53a, an elastic layer 53b, and a release layer 53c. The pressure roller 53 is rotatably supported at both longitudinal ends and is driven to rotate by a fixing motor 100 (FIG. 2). The film 51 is driven to rotate as the pressure roller 53 rotates. The fixing motor 100 is located on the front side of FIG. 3 and drives the pressure roller 53. Hereinafter, the side of the pressure roller 53 where the fixing motor 100 is located is referred to as the drive side, and the side of the pressure roller 53 opposite the side where the fixing motor 100 is located is referred to as the non-drive side.

[0028] Heater 54, which is a heating member, is disposed in the internal space of fixing film 51 and is held with one end in the longitudinal direction abutting against heater holder 52. A protrusion is formed at the position of heater holder 52 where heater 54 abuts, and defines the longitudinal position of heater 54. Heater 54 held by heater holder 52 is in contact with the inner surface of film 51. Heater substrate 54a, heating elements 54b1 (54b1a, 54b1b), 54b2, 54b3, protective glass layer 54e, and fixing temperature sensor 59 (not shown in FIG. 3) will be described later.

[0029] [Overview of the heater section] Next, the heater 54, which is a heating unit, will be described. FIG. 4(a) is a schematic diagram showing the configuration of the heater 54, in which the heating elements are arranged, as viewed from the pressure roller 53 side shown in FIG. 3. In FIG. 4(a), reference line a is the longitudinal center line of the heating elements 54b1a, 54b1b, 54b2, and 54b3, and is also the longitudinal center line (paper width direction) of the paper P transported to the fixing nip N of the fixing device 50. As shown in FIG. 4(a), the heater 54 includes a heater substrate 54a, heating elements 54b1a, 54b1b, 54b2, and 54b3, a conductor 54c, contacts 54d1 to 54d4, and a protective glass layer 54e. The conductor 54c is the black portion in the drawing. Hereinafter, the heating elements 54b1a, 54b1b, 54b2, and 54b3 may be collectively referred to as heating element 54b.

[0030] In this embodiment, the heater substrate 54a has an elongated shape and is made of alumina (Al2O3), a ceramic material. Widely known ceramic substrates include alumina (Al2O3), aluminum nitride (AlN), zirconia (ZrO2), and silicon carbide (SiC). Among these, alumina (Al2O3) is inexpensive and readily available. Alternatively, the heater substrate 54a may be made of a metal, which offers excellent strength. When using a metal substrate, stainless steel (SUS) is preferred due to its cost and strength. Whether the substrate is ceramic or metal, if it is conductive, an insulating layer may be provided. Heating elements 54b1a, 54b1b, 54b2, and 54b3, a conductor 54c, and contacts 54d1 through 54d4 are arranged on the heater substrate 54a (substrate), and a protective glass layer 54e is coated on top of the substrate to ensure insulation between the heating elements and the film 51.

[0031] The longitudinal positional relationship of the heating elements 54b will now be described. Each heating element has a different longitudinal length (length in the left-right direction in FIG. 4(a)). The longitudinal length L1 of heating elements 54b1a and 54b1b is 222 mm, the longitudinal length L2 of heating element 54b2 is 188 mm, and the longitudinal length L3 of heating element 54b3 is 154 mm. The longitudinal lengths L1, L2, and L3 are in the order L1 > L2 > L3. The heating elements are arranged in the short-side direction (vertical direction in FIG. 4(a)) in the order of heating elements 54b1a, 54b2, 54b3, and 54b1b. The heating elements 54b1 (54b1a, 54b1b), 54b2, and 54b3 are arranged on the heater substrate 54a with their longitudinal centers aligned. Furthermore, the largest paper width (hereinafter referred to as the maximum paper width) of the paper P that can be used in the image forming apparatus of this embodiment is 216 mm, and the smallest paper width (hereinafter referred to as the minimum paper width) is 76 mm. Therefore, the heating element 54b1, whose longitudinal length is length L1 (222 mm), has a length that allows it to fix an image size (206 mm) for the maximum paper width (216 mm).

[0032] As shown in FIG. 4(a), heating elements 54b1a and 54b1b are electrically connected at one end to contact 54d2 (first contact) and at the other end to contact 54d4 (fourth contact) via conductor 54c. Heating element 54b2 (third heating element) is electrically connected at one end to contact 54d2 and at the other end to contact 54d3 (third contact) via conductor 54c. Similarly, heating element 54b3 (fourth heating element) is electrically connected at one end to contact 54d1 (second contact) and at the other end to contact 54d3 via conductor 54c. As shown in FIG. 4(a), heating elements 54b1a and 54b1b have the same longitudinal length L1, and these two heating elements 54b1a and 54b1b are always used simultaneously. Hereinafter, the pair of heating elements 54b1a and 54b1b will be collectively referred to as heating element 54b1. Heating element 54b1a (first heating element) is disposed at one end of heater substrate 54a in the short side direction, and heating element 54b1b (second heating element) is disposed at the other end of heater substrate 54a in the short side direction. Heating elements 54b2 and 54b3 are disposed symmetrically with respect to the center of the short side direction between heating elements 54b1a and 54b1b in the short side direction of heater substrate 54a.

[0033] [Heat-equalizing material] 3, in this embodiment, an aluminum plate 60, which is a temperature equalizing member for equalizing the temperature of the heater substrate 54a, is installed between the heater holder 52 and the heater 54. The aluminum plate 60 is located on the opposite side of the heater substrate 54a from the heating element 54b and the protective glass layer 54e.

[0034] The aluminum plate 60 has a thickness of 0.3 mm, a length in the short direction of 7 mm, and a length in the long direction of 222 mm, which is the same length as the heating element 54b1. A positioning portion 60a (also referred to as a bent portion) (see FIG. 7) bent toward the heater holder 52 is formed at one location in the long direction of the aluminum plate 60. The positioning portion 60a fits into a positioning recess formed in the heater holder 52, thereby determining the longitudinal position of the aluminum plate 60. In this embodiment, the shape of the positioning portion 60a of the aluminum plate 60 is formed by bending the aluminum plate 60, but the shape is not limited to this and may be formed by, for example, a casting process, cutting process, drawing process, or the like.

[0035] [Fuser temperature sensor] 4(a), the fixing temperature sensor 59 is surrounded by a dashed line. The dashed line indicates that the fixing temperature sensor 59 is disposed on the rear surface of the heater substrate 54a (opposite the surface on which the heating elements 54b1, 54b2, and 54b3 are disposed), and also indicates the position where the fixing temperature sensor 59 abuts against the heater substrate 54a. A main thermistor 59a that detects the temperature of the fixing temperature sensor 59 is disposed on the center line of the heating elements 54b1, 54b2, and 54b3 in the short direction, and on a reference line a that is the center line of the paper P transported to the fixing device 50.

[0036] FIG. 4(b) is a schematic diagram showing a cross section of the heater 54 shown in FIG. 4(a) when the heater 54 is cut along the center line (reference line a in FIG. 4(a)) in the longitudinal direction of the paper P being conveyed to the fixing device 50. The fixing temperature sensor 59, which is a temperature detection means for detecting the temperature of the heater 54, has the following components: a main thermistor 59a, a holder 59b, ceramic paper 59c that blocks heat conduction between the holder 59b and the main thermistor 59a, and an insulating resin sheet 59d that physically and electrically protects the main thermistor 59a. The main thermistor 59a is a temperature detection element whose resistance value changes in response to the temperature of the heater 54, and whose output voltage changes. The main thermistor 59a is connected to the CPU 94 by a dumet wire (not shown) and wiring. The main thermistor 59a detects the temperature of the heater 54 via an aluminum plate 60 and outputs a voltage corresponding to the temperature of the heater 54 to the CPU 94. The CPU 94 controls the temperature of the heater 54 during the fixing process based on the temperature detection result of the fixing temperature sensor 59 (main thermistor 59a).

[0037] As shown in FIG. 4(a), the fixing temperature sensor 59 is disposed at the reference line a in the longitudinal direction of the heat generating element 54b, and is in contact with the aluminum plate 60. The fixing temperature sensor 59 is disposed at the center of the heater substrate 54a in the lateral direction. That is, the fixing temperature sensor 59 is disposed at approximately equal distances in the lateral direction from the heat generating elements 54b2 and 54b3. Therefore, even when either the heat generating element 54b2 or the heat generating element 54b3 is heated, the fixing temperature sensor 59 can detect the temperature of the heater substrate 54a, and the same applies to the two heat generating elements 54b1.

[0038] [Power Control Unit] 5 is a schematic circuit diagram of a power control circuit in which a power control unit 97 of the fixing device 50 controls the power supply from an AC power supply 55 to a heater 54 having heating elements 54b1, 54b2, and 54b3. The power control circuit of the fixing device 50 is composed of triacs 56a, 56b, and 56c and a heating element switch 57. A contact 54d1 of the heater 54 is connected to a triac 56c (third switch) and is connected to a first pole of the AC power supply 55 via the triac 56c. A contact 54d2 of the heater 54 is connected to the heating element switch 57 and a second pole of the AC power supply 55. A contact 54d3 of the heater 54 is connected to a triac 56b (second switch) and the heating element switch 57 and is connected to a first pole of the AC power supply 55 via the triac 56b. The contact 54d4 of the heater 54 is connected to a triac 56a (first switch) and to a first pole of the AC power supply 55 via the triac 56a. The heating element switch 57 switches the power supply path, thereby switching the heating element 54b to which power is supplied from the AC power supply 55. Therefore, in this embodiment, "switching the power supply path" is also expressed as "switching the heating element 54b." In this embodiment, the heating element switch 57 is specifically an electromagnetic relay with an a-contact configuration. The triacs 56a, 56b, and 56c are set to a conductive or non-conductive state, thereby supplying or cutting off power from the AC power supply 55 to the heating elements 54b1, 54b2, and 54b3. The CPU 94 calculates the amount of power required to set the heater 54 to a predetermined temperature (the target temperature required for fixing) based on the temperature information of the heater 54 acquired from the main thermistor element 59a. The CPU 94 then instructs the power control unit 97 to set the conductive / non-conductive states of the triacs 56a, 56b, and 56c. Based on the setting instruction from the CPU 94 of the engine controller 92, the heating element switch 57 is set to either a state in which the contacts 54d2 and 54d3 are connected, or a state in which the contacts 54d2 and 54d3 are disconnected.

[0039] [Power supply route] Next, a method of supplying power from AC power supply 55 to the heating elements by alternately switching between heating elements 54b1 and 54b2, and between heating elements 54b1 and 54b3 will be described. FIG. 6 is a diagram illustrating a supply path for supplying power from AC power supply 55 in the circuit schematic diagram described in FIG. 5. In FIG. 6, in heater 54 in which three types of heating elements 54b1, 54b2, and 54b3 with different longitudinal lengths are arranged, three current paths (electrical paths and power supply paths) to each of heating elements 54b1, 54b2, and 54b3 are shown by thick solid lines. Note that the current paths shown in FIG. 6 are just an example, and other current path configurations may be used.

[0040] (Power supply to heating element 54b1) When power is supplied from the AC power supply 55 to the heating element 54b1, the current flows through the current path indicated by the thick line in FIG. 6(a). The fixing temperature sensor 59 (not shown in FIG. 6) detects the temperature of the heater 54, and the CPU 94 operates the triac 56a based on the temperature information acquired from the fixing temperature sensor 59 so that the temperature of the heater 54 reaches a predetermined temperature. This controls the power supply from the AC power supply 55 to the heating element 54b1. The power supply to the heating element 54b1 is only required for the triac 56a to be in a conductive state, and is not dependent on the states of the triacs 56b and 56c or the state (open or short-circuited) of the heating element switch 57. In other words, when power is supplied to the heating element 54b1, the heating element switch 57 may be in an open or short-circuited state. In FIG. 6(a), the heating element switch 57 is in an open state, for example.

[0041] In this embodiment, by setting triacs 56a and 56b to a conductive state, triac 56c to a non-conductive state, and heating element switch 57 to an open state, it is possible to simultaneously supply power to heating elements 54b1 and 54b2 from AC power supply 55. Similarly, by setting triacs 56a and 56c to a conductive state, triac 56b to a non-conductive state, and heating element switch 57 to a short-circuited state, it is possible to simultaneously supply power to heating elements 54b1 and 54b3 from AC power supply 55. When power is to be supplied from AC power supply 55 only to heating element 54b1, triac 56a is set to a conductive state, and triacs 56b and 56c are set to a non-conductive state.

[0042] (Power supply to heating element 54b2) When power is supplied from AC power supply 55 to heating element 54b2, current flows through the current path indicated by the bold line in FIG. 6(b). When power is supplied to heating element 54b2, triac 56b is set to a conductive state, and the contacts of heating element switch 57 are set to an open state. In the open state, the contact impedance of heating element switch 57 is sufficiently greater than the impedance of heating element 54b2. Therefore, current from AC power supply 55 flows to heating element 54b2, and almost no current flows through heating element switch 57, allowing only heating element 54b2 to be heated. The power supplied to heating element 54b2 is controlled by triac 56b, and when power is supplied only to heating element 54b2, triacs 56a and 56c are set to a non-conductive state.

[0043] (Power supply to heating element 54b3) When power is supplied from AC power supply 55 to heating element 54b3, the current flows through the current path indicated by the thick line in Figure 6(c). When power is supplied to heating element 54b3, triac 56c is set to a conductive state, and the contacts of heating element switch 57 are set to a short-circuited state. As a result, almost all of the current from AC power supply 55 flows to heating element 54b3. Because the contact impedance of heating element switch 57 in the short-circuited state is sufficiently smaller than the impedance of heating element 54b2, almost no current flows to heating element 54b2, allowing only heating element 54b3 to generate heat. The power supplied to heating element 54b3 is controlled by triac 56c, and when power is supplied only to heating element 54b3, triacs 56a and 56b are set to a non-conductive state.

[0044] [Power supply path switching] As described above, when power is supplied from AC power supply 55 to heating element 54b1, heating element switch 57 may be in an open or short-circuited state. However, when power is supplied to heating element 54b2, the contacts of heating element switch 57 must be set to an open state. Therefore, when switching between the power supply path to heating element 54b1 shown in FIG. 6(a) (hereinafter referred to as power supply path 1) and the power supply path to heating element 54b2 shown in FIG. 6(b) (hereinafter referred to as power supply path 2), the contacts of heating element switch 57 are set to an open state in advance. This allows the triacs 56a and 56b, which are contactless switches, to be independently controlled to switch the power supply path. That is, by switching the conductive and non-conductive states of triacs 56a and 56b between power supply path 1 (FIG. 6(a)) and power supply path 2 (FIG. 6(b)), a seamless state transition can be achieved, or power supply path 1 and power supply path 2 can be used simultaneously.

[0045] Similarly, the power supply path 1 to the heating element 54b1 (FIG. 6(a)) and the power supply path to the heating element 54b3 shown in FIG. 6(c) (hereinafter referred to as power supply path 3) can be switched between in the same way. As described above, in the power supply path 1 that supplies power to the heating element 54b1, the heating element switch 57 may be in an open state or a short-circuited state. On the other hand, when supplying power to the heating element 54b3, the contacts of the heating element switch 57 must be set to a short-circuited state. Therefore, when switching between the power supply path 1 and the power supply path 3, if the contacts of the heating element switch 57 are short-circuited in advance, the following becomes possible. That is, by switching the conductive and non-conductive states of the triacs 56a and 56c between the power supply path 1 (FIG. 6(a)) and the power supply path 3 (FIG. 6(c)), a seamless state transition can be achieved, or the power supply path 1 and the power supply path 3 can be used simultaneously.

[0046] On the other hand, when supplying power to heating element 54b2, the contacts of heating element switch 57 must be set to an open state, and when supplying power to heating element 54b3, the contacts of heating element switch 57 must be set to a short-circuit state. Therefore, when switching between power supply path 2 (FIG. 6(b)) for heating element 54b2 and power supply path 3 (FIG. 6(c)) for heating element 54b3, the state of heating element switch 57 must be switched. In other words, only one of power supply path 2 (FIG. 6(b)) and power supply path 3 (FIG. 6(c)) can be used; they are mutually exclusive. Furthermore, unlike triacs 56a, 56b, and 56c, which are contactless switches, heating element switch 57 with an a-contact configuration requires time for the state to stabilize after switching the contact state.

[0047] Therefore, when transitioning between power supply path 2 ( FIG. 6( b)) and power supply path 3 ( FIG. 6(c)), the following procedure can be used. For example, a state transition can be performed from power supply path 2 ( FIG. 6(b)) to power supply path 1 ( FIG. 6(a)) to power supply path 3 ( FIG. 6(c)), or from power supply path 3 ( FIG. 6(c)) to power supply path 1 ( FIG. 6(a)) to power supply path 2 ( FIG. 6(b)). For either state transition, power supply path 1 ( FIG. 6(a)) can be passed between power supply path 2 ( FIG. 6(b)) and power supply path 3 ( FIG. 6(c)). While power supply path 1 ( FIG. 6(a)) is being used, i.e., while power is being supplied to the heating element 54b1, the state of the heating element switch 57, which has an a-contact configuration, is switched from an open state to a short-circuit state, or from a short-circuit state to an open state. By providing the power supply path 1, a period is provided until the state of the contact of the heating element switch 57 having the contact a configuration becomes stable. This makes it possible to avoid a situation in which the power supply from the AC power supply 55 to the heater 54 is cut off due to an unstable state of the heating element switch 57, making it impossible to supply the amount of heat required to heat the paper P.

[0048] [Heat equalizing member positioning part] Here, the positional relationship between the positioning portion 60a of the aluminum plate 60, which is a temperature equalizing member characteristic of this embodiment, relative to the heater holder 52, and the heating element 54b of the heater 54 will be described. First, the shape of the aluminum plate 60 will be described using FIG. 7. FIG. 7(a) is a top view showing the shape of the aluminum plate 60 as viewed from the heater holder 52 side, and the arrow on the right indicates the conveyance direction of the paper P shown in FIG. 3. FIG. 7(b) is a side view of the aluminum plate 60 as viewed from the drive side (the side of the fixing motor 100 that drives the pressure roller 53 in FIG. 3). In FIG. 7(b), the surface of the aluminum plate 60 that contacts the heater holder 52 is the upper surface in the figure, and surface 60b is the contact surface that contacts the heater substrate 54a.

[0049] In FIG. 7(a), the positioning portion 60a fits into a positioning recess formed in the heater holder 52 to regulate (determine) the longitudinal position of the aluminum plate 60. The positioning portion 60a has a longitudinal width H1 (FIG. 7(a)) of 5 mm and a height h1 (FIG. 7(b)) of 3 mm, and is formed perpendicular to the contact surface 60b. The aluminum plate 60 is positioned in the longitudinal direction by the positioning portion 60a fitting into the recess formed in the heater holder 52. As described above, the longitudinal position of the heater 54 relative to the heater holder 52 is determined by abutting the drive-side side of the heater 54 against a heater abutment formed in the heater holder 52. Therefore, the longitudinal positional relationship between the aluminum plate 60 and the heater 54 is regulated via the heater holder 52.

[0050] [Positional relationship between the heat equalizing element and the heater's heating element] FIG. 8 is a diagram showing the positional relationship between the heater 54 and the aluminum plate 60 in this embodiment. In FIG. 8, the upper diagram shows the positions of the heating elements 54b1 (54b1a, 54b1b), 54b2, and 54b3 of the heater 54 described in FIG. 4. Meanwhile, the lower diagram shows the aluminum plate 60, which is arranged on the surface of the heater 54 opposite to the surface on which the heating element 54b is arranged, as viewed from the side on which the heating element 54b is arranged. The area surrounded by a dotted line indicates the position where the positioning portion 60a is provided. Note that the position of the positioning portion 60a shown in FIG. 8 is an example, and as will be described later, the positioning portion 60a is arranged at a position at least partially within the region corresponding to the longest heating element 54b1 when viewed in the short-side direction of the heater substrate 54a.

[0051] As described above, the heating elements 54b1 (54b1a, 54b1b), 54b2, and 54b3 are arranged on the heater substrate 54a with their longitudinal centers aligned. The heating elements 54b1 (54b1a, 54b1b) have a longitudinal length of 222 mm. The heating element 54b2 has a longitudinal length of 188 mm, and its longitudinal end is located 17 mm (=(222 mm-188 mm) / 2) inward from the longitudinal end of the heating element 54b1. The heating element 54b3 has a longitudinal length of 154 mm, and its longitudinal end is located 34 mm (=(222 mm-154 mm) / 2) inward from the longitudinal end of the heating element 54b1.

[0052] Meanwhile, both longitudinal ends of the aluminum plate 60 are positioned at approximately the same positions as both longitudinal ends of the heating element 54b1. The positioning portion 60a of the aluminum plate 60 is formed 5 mm from a position 5 mm from the driving-side end of the aluminum plate 60 (the right end of the aluminum plate 60 in the figure) to a length of 5 mm in the longitudinal direction to the left in the figure. That is, as shown in FIG. 8, at least a portion of the positioning portion 60a of the aluminum plate 60 is positioned in a position corresponding to an area where only the heating element 54b1, which is symmetrically arranged at the end of the heater substrate 54a in the lateral direction, is arranged (heating element 54b1b in FIG. 8). The positioning portion 60a of the aluminum plate 60 is not positioned in a position corresponding to an area where the heating elements 54b2 and 54b3, which are not arranged at the end of the heater substrate 54a in the lateral direction (arranged in the center in the lateral direction), are arranged. That is, the positioning portion 60a of the aluminum plate 60 is positioned outside the area where the heating elements 54b2 and 54b3 are arranged.

[0053] If a temperature gradient occurs in the short-side direction of the heater substrate 54a, distortion occurs within the heater substrate 54a due to differences in the amount of thermal expansion. Furthermore, if a part of the fixing device 50 malfunctions and excessive power is supplied to the heating element 54b, deformation of the heater substrate 54a may occur. Such deformation of the heater substrate 54a becomes more pronounced when heating elements (e.g., heating elements 54b2 and 54b3 in this embodiment) that are not symmetrically arranged at both ends of the short-side direction of the heater substrate 54a generate heat.

[0054] When heating elements positioned asymmetrically at both ends of the heater substrate 54a relative to the centerline of the heater substrate 54a in the lateral direction generate heat, the temperature of the heater substrate 54a at the positions where the heating elements are located increases. Meanwhile, the end portions of the heater substrate 54a in the lateral direction have a large surface area, resulting in a large amount of heat dissipation. This is particularly noticeable at the end portions of the heater substrate 54a where there are no heating elements positioned asymmetrically at both ends of the heater substrate 54a in the lateral direction. As a result, the temperature of the heater substrate 54a decreases, and the temperature gradient in the lateral direction of the heater substrate 54a increases. Therefore, when power is supplied to heating elements positioned near the center of the heater substrate 54a in the lateral direction (54b2 and 54b3 in this embodiment), the heater substrate 54a deforms more due to the difference in thermal expansion caused by the temperature difference within the heater substrate 54a. This is particularly noticeable when the heating elements are positioned asymmetrically off-center rather than at the center of the heater substrate 54a in the lateral direction. On the other hand, in the case of the heating element (54b1 in this embodiment) arranged symmetrically at both ends of the heater substrate 54a in the short direction, the ends in the short direction where the heating element is arranged are less affected by the large amount of heat dissipation, and the temperature gradient in the short direction of the heater substrate 54a is less likely to become large.

[0055] As described above, in this embodiment, the positioning portion 60a of the aluminum plate 60, which is a heat-equalizing member with a large heat capacity that easily absorbs heat from the heater substrate 54a, is provided in the following position. That is, the positioning portion 60a is not positioned so as to overlap, via the heater substrate 54a, with the heating elements 54b2 and 54b3, which are positioned asymmetrically with respect to the center line of the heater substrate 54a in the lateral direction. Furthermore, the positioning portion 60a is positioned so that at least a portion of the positioning portion 60a overlaps, via the heater substrate 54a, with the heating element 54b1, which is positioned symmetrically at the end of the heater substrate 54a in the lateral direction. This reduces the increase in the thermal gradient when the heating element 54b generates heat, and suppresses deformation due to distortion of the heater substrate 54a.

[0056] As described above, according to this embodiment, it is possible to suppress deformation of the heater substrate due to the positioning portion of the temperature equalizing member. [Example]

[0057] In the second embodiment, a power control circuit having a different configuration from that of the first embodiment, and a heating element and a heat equalizing member having different shapes from those of the first embodiment will be described. Note that the configuration of the image forming apparatus used in the second embodiment is the same as that of the first embodiment, and the same members will be designated by the same reference numerals, and the description thereof will be omitted.

[0058] [Power Control Unit] FIG. 9 is a schematic circuit diagram of a power control circuit in which power control unit 97 of fixing device 50 of this embodiment controls the power supply from AC power supply 55 to heater 154, which has heating elements 154b1, 154b2, and 154b3. In FIG. 9, heater 154 is composed of heater substrate 154a, heating elements 154b1a, 154b1b, 154b2, and 154b3, conductor 154c, contacts 154d1-154d4, and protective glass layer 154e (not shown in FIG. 9). Heating elements 154b1 (154b1a and 154b1b), 154b2, and 154b3 are arranged on heater substrate 154a with their longitudinal centers aligned. In this embodiment, as will be described later, the shape of both longitudinal end portions of heating element 154b1 differs from that of embodiment 1.

[0059] The power control circuit of the fixing device 50 of this embodiment is composed of triacs 156a and 156b, and a heating element switch 157 which is a contact C relay. A contact 154d1 of the heater 154 is connected to a triac 156b (second switch) and a first contact of the heating element switch 157, and is connected to a first pole of the AC power supply 55 via the triac 156b. A contact 154d2 of the heater 154 is connected to a second contact of the heating element switch 157 and a second pole of the AC power supply 55. A contact 154d3 of the heater 154 is connected to the heating element switch 157. A contact 154d4 of the heater 154 is connected to a triac 156a (first switch), and is connected to a first pole of the AC power supply 55 via the triac 156a.

[0060] When power is to be supplied to heating element 154b1, triac 156a is set to a conductive state, thereby supplying power from AC power supply 55. When power is to be supplied to heating element 154b2, triac 156b is set to a conductive state and connected to the first contact of heating element switch 157, thereby supplying power from AC power supply 55. When power is to be supplied to heating element 154b3, triac 156b is set to a conductive state and connected to the second contact of heating element switch 157, thereby supplying power from AC power supply 55. As described above, in this embodiment, as shown in FIG. 9, triac 156a is connected to heating element 154b1, and heating element 154b2 or heating element 154b3 is selected by a contact c relay constituting heating element switch 157.

[0061] [Heater configuration] FIG. 10 is an enlarged view of the right-side longitudinal end of heater 154 of this embodiment shown in FIG. 9, showing the positional relationship with the heating elements when a standard-sized sheet P is passed through fixing device 50. In FIG. 10, (a) is an enlarged view of the right-side longitudinal end of heater 154, showing the shapes of heating elements 154b1a and 154b1b, and (b) is a view illustrating the regions near the longitudinal ends of heating elements 154b1a and 154b1b. FIG. 10(c) is a view illustrating the positional relationship when LTR paper (letter paper) is passed through heating elements 154b1a and 154b1b shown in FIG. 10(a). And FIG. 10(d) is a view illustrating the positional relationship when A4-size paper (referred to as A4 paper in the drawing) is passed through heating elements 154b1a and 154b1b shown in FIG. 10(a).

[0062] As shown in Figures 10(a) and (b), at the longitudinal ends of the heating elements 154b1a and 154b1b, a region where the width in the short side direction gradually narrows from width H2 to width H3 is designated as region F (Figure 10(b)). Also, a region adjacent to region F where the width in the short side direction gradually widens from width H3 to width H4 is designated as region G (Figure 10(b)). And a region where the width in the short side direction is constant at width H4 is designated as region H (Figure 10(b)).

[0063] In region F of the heating elements 154b1a and 154b1b, the width in the short-side direction gradually narrows from width H2 to width H3 toward the center in the longitudinal direction. In this embodiment, width H2 is 1.0 mm, and width H3 is 0.7 mm. While the width of region F narrows linearly in FIG. 10(a), it may narrow in a curved manner, for example. Furthermore, the longitudinal length L4 of region F is 6 mm. Next, region G will be described. In region G of the heating elements 154b1a and 154b1b, the width in the short-side direction gradually widens from width H3 to width H4 toward the center in the longitudinal direction. In this embodiment, width H4 is 0.8 mm. Therefore, the size relationship among widths H2, H3, and H4 is width H2 > width H4 > width H3. While the width of region G narrows linearly in FIG. 10, it may narrow in a curved manner, for example. The longitudinal length L5 of region G is 22 mm. Furthermore, the width H4 (first length) of the region H of the heating element 154b1a in the short-side direction is constant at 0.8 mm, and the length L6 from the center of the region H in the long-side direction is 83 mm (= (222 mm / 2) - 6 mm - 22 mm). Therefore, the relationship in magnitude between the lengths L4, L5, and L6 of the regions F, G, and H is length L6 > length L5 > length L4. Furthermore, as shown in FIG. 10(a), the heating elements 154b1a and 154b1b are symmetrical (vertically symmetrical) with respect to the center (middle) in the short-side direction of the heater substrate 154a, and have the same dimensions as the heating element 154b1a. 10(a) is an enlarged view of the vicinity of the right end portion in the longitudinal direction of heater 154 shown in Fig. 9, and the shapes of heat generating elements 154b1a and 154b1b on the left side in the longitudinal direction of heater 154 are not shown, but are symmetrical to the shape on the right side shown in Fig. 10(a). In other words, the longitudinal shapes of heat generating elements 154b1a and 154b1b are symmetrical (bilaterally symmetrical in Fig. 10) with respect to the center (center) in the longitudinal direction of heater substrate 154a.

[0064] The reason for the above-described shapes of the heating elements 154b1a and 154b1b is to increase the amount of heat generated per unit length (energy density P) in the order of regions G, H, and F when a voltage is applied to the heating elements 154b1a and 154b1b from the AC power supply 55. That is, if the energy densities in regions F, G, and H are P1, P2, and P3, respectively, the magnitude relationship is desired to be P2>P3>P1. Here, the average width of region F in the short side direction (average of width H2 and width H3) is set to width H23 (third length) (= (width H2 (1.0 mm) + width H3 (0.7 mm)) / 2 = 0.85 mm). Furthermore, the average width of region G in the short side direction (average of width H3 and width H4) is set to width H34 (second length) (= (width H3 (0.7 mm) + width H4 (0.8 mm)) / 2 = 0.75 mm). In this case, for the heating elements 154b1a and 154b1b of Example 2, the following relationship holds: width H23 (0.85 mm) of region F > width H4 (0.8 mm) of region H > width H34 (0.75 mm) of region G. Here, R1 denotes the electrical resistance per unit length of region F, which is the region closest to the longitudinal end of the heating elements 154b1a and 154b1b; R2 denotes the electrical resistance of region G adjacent to region F; and R3 denotes the electrical resistance of region H, which is located at the center in the longitudinal direction. The electrical resistance of each region is proportional to the length of the region and inversely proportional to the cross-sectional area (the width in the lateral direction in this case). Therefore, the relationship between the electrical resistances R1, R2, and R3 is R2 > R3 > R1, with the electrical resistance per unit length of each region being greatest in region G, followed by region H and region F, in that order. As a result, when a voltage is applied to the heating elements 154b1a and 154b1b, the amount of heat generated (energy density) per unit length increases in the order of regions G, H, and F. The magnitude relationship of the energy densities of the regions is energy density P2 (heat generation amount P2) of region G > energy density P3 (heat generation amount P1) of region H > energy density P1 (heat generation amount P3) of region F.

[0065] [Positional relationship between paper and heating element] FIG. 10(c) illustrates the positional relationship between LTR paper, which is the paper P with the longest longitudinal length, and regions F, G, and H of heating elements 154b1a and 154b1b. FIG. 10(d) illustrates the positional relationship between A4 paper, which is the paper P with the second longest longitudinal length after LTR paper, and regions F, G, and H of heating elements 154b1a and 154b1b. In FIGS. 10(c) and 10(d), the top of the paper indicates the leading edge of the paper in the paper transport direction. A 5-mm margin is provided from the leading edge and the right edge of the paper in the figure. The black portion outside the margin indicates the image area to be printed. The trailing edge of the paper and the left edge of the paper in the figure are not illustrated, but both have a 5-mm margin. As shown in FIG. 10(c), the longitudinal edge of the image area of ​​LTR paper passes through the fixing nip N area corresponding to region G of high energy density of heating elements 154b1a and 154b1b. 10(d), the region F of the heating elements 154b1a and 154b1b corresponding to the non-paper passing region of the fixing nip N where the longitudinal edge of an A4 sheet of paper does not pass is a region with low energy density. This suppresses temperature rise in the non-paper passing region (non-paper passing portion) of the fixing nip N corresponding to region F, and also reduces the temperature drop at the longitudinal edge, where the amount of heat dissipation is large, compared to the longitudinal center portion.

[0066] [Shape of heat equalizing member and configuration of positioning part] 11 is a top view showing the shape of aluminum plates 161 and 162, which are the heat equalizing members of this embodiment, as viewed from the heater holder 52 side, and the arrow on the right indicates the conveyance direction of paper P shown in FIG. 3. While aluminum plate 60, which is the heat equalizing member of Example 1, was a single member, the heat equalizing member of this embodiment is composed of two aluminum plates 161 and 162. The driving-side aluminum plate 161 (first heat equalizing member) and the non-driving-side aluminum plate 162 (second heat equalizing member) are arranged symmetrically with respect to the center of the heater 154 in the longitudinal direction of the fixing device 50. That is, aluminum plate 161 is arranged at one end of heater 154 in the longitudinal direction of heater 154, and aluminum plate 162 is arranged at the other end of heater 154 in the longitudinal direction of heater 154. The ends of the aluminum plates 161 and 162 opposite to the center end in the longitudinal direction are positioned at approximately the same positions as the ends of the heating element 154b1, via the heater substrate 154a. A gap is provided between the two aluminum plates 161 and 162 to prevent them from interfering with each other when they thermally expand. The aluminum plates 161 and 162 are each formed with a positioning portion 161a (first positioning portion) and a positioning portion 162a (second positioning portion) for positioning them relative to the heater holder 152 (not shown). Similar to the positioning portion 60a in Example 1, the positioning portions 161a and 162a are formed by, for example, bending an aluminum plate, and have a width H1 (length) of 5 mm in the longitudinal direction and a height of 3 mm in the direction of the heater holder 152. The heater holder 152 is formed with positioning holes into which the positioning portions 161a and 162a formed on the aluminum plates 161 and 162, respectively, fit. Positioning portions 161a and 162a of aluminum plates 161 and 162 are fitted into positioning holes of heater holder 152, respectively, thereby defining the longitudinal positions of aluminum plates 161 and 162 relative to heater holder 152.

[0067] [Positional relationship between the heat equalizing element and the heater's heating element] Fig. 12 is a diagram showing the positional relationship between heater 154 and aluminum plates 161 and 162 in this embodiment. In Fig. 12, the upper diagram shows the arrangement positions of heating elements 154b1 (154b1a, 154b1b), 154b2, and 154b3 of heater 154 described in Fig. 9. Meanwhile, the lower diagram shows aluminum plates 161 and 162, which are arranged on the surface of heater substrate 154a opposite to the surface on which heating elements 154b1, 154b2, and 154b3 are arranged, as viewed from the side on which the heating elements are arranged. The areas surrounded by dotted lines indicate the positions where positioning portions 161a and 162a are provided.

[0068] Positioning portion 161a of aluminum plate 161 arranged on the driving side is formed from a position 5 mm from the driving side end of aluminum plate 161 (the right end of aluminum plate 161 in the figure) to a length of 5 mm in the left direction in the figure toward the center in the longitudinal direction. Positioning portion 162a of aluminum plate 162 arranged on the non-driving side is formed from a position 5 mm from the non-driving side end of aluminum plate 162 (the left end of aluminum plate 161 in the figure) to a length of 5 mm in the right direction in the figure toward the center in the longitudinal direction.

[0069] As described above, the heating elements 154b1 (154b1a, 154b1b), 154b2, and 154b3 are arranged on the heater substrate 154a with their longitudinal centers aligned. The heating elements 154b1 (154b1a, 154b1b) have a longitudinal length of 222 mm. The heating element 154b2 has a longitudinal length of 188 mm, and its longitudinal end is located 17 mm (=(222 mm-188 mm) / 2) inward from the longitudinal end of the heating element 154b1. The heating element 154b3 has a longitudinal length of 154 mm, and its longitudinal end is located 34 mm (=(222 mm-154 mm) / 2) inward from the longitudinal end of the heating element 154b1. That is, in this embodiment, the longitudinal positioning portions 161a and 162a of the two divided aluminum plates 161 and 162 are arranged in the following positions: The positioning portions 161a and 162a are not arranged in positions that overlap with the heating elements 154b2 and 154b3, which are arranged asymmetrically with respect to the center line of the heater substrate 154a in the lateral direction, with the heater substrate 154a interposed therebetween. The positioning portions 161a and 162a are arranged in positions that overlap with the heating element 154b1, which is arranged symmetrically at the end of the heater substrate 154a in the lateral direction, with the heater substrate 154a interposed therebetween, with at least a portion of the positioning portions 161a and 162a interposed therebetween. This reduces the increase in the thermal gradient within the heater substrate 154a when the heating elements generate heat, and suppresses deformation of the heater substrate 154a due to distortion.

[0070] Furthermore, in this embodiment, the aluminum plates 161 and 162 serving as the temperature equalizing members disposed on the rear surface of the heater 154a (the surface opposite the surface in contact with the film 51) are separated into two bodies (two members) rather than a single component, which offers the following advantages. The temperature equalizing members disposed on the rear surface of the heater substrate 154a are heated by the heat generated by the heater 154 and thermally expand. When the heater 154 stops heating and the temperature drops, the aluminum plates 161 and 162 serving as the temperature equalizing members attempt to shrink back to their original dimensions. However, because they are strongly pressed between the heater 154 and the heater holder 152 by the pressure from the pressure roller 53, they do not fully return to their original dimensions. Repeating this process can result in a change in the dimensions of the temperature equalizing members. This phenomenon is particularly noticeable when the temperature equalizing members are made of a metal, such as aluminum, that has a different thermal expansion rate from the heater substrate 154a. Therefore, by dividing the aluminum plate serving as the temperature equalizing member into multiple pieces, the amount of expansion is reduced, thereby minimizing such dimensional changes.

[0071] As described above, according to this embodiment, it is possible to suppress deformation of the heater substrate due to the positioning portion of the temperature equalizing member. [Example]

[0072] In the third embodiment, an embodiment will be described in which the configuration of the heating element of the heater and the configuration of the power control circuit are different from those of the first and second embodiments. Note that the configuration of the image forming apparatus used in the third embodiment is the same as that of the first embodiment, and the same members are designated by the same reference numerals, and the description thereof will be omitted.

[0073] [Heater configuration] FIG. 13 is a schematic circuit diagram of a power control circuit in which power control unit 97 of fixing device 50 controls the power supply from AC power supply 55 to heater 254, which has heating elements 254b1 (254b1a, 254b1b) and 254b2. In FIG. 13, heater 254 is composed of heater substrate 254a, heating elements 254b1a, 254b1b, and 254b2, conductor 254c, contacts 254d1-254d3, and protective glass layer 254e (not shown in FIG. 13). The longitudinal length L1 of heating elements 254b1a and 254b1b is 222 mm, the same as that of heating elements 54b1a and 54b1b in Example 1. Furthermore, the longitudinal length L2 of heating element 254b2 is 188 mm. The heating elements 254b1 (254b1a, 254b1b) and 254b2 are arranged on the heater substrate 254a with their longitudinal centers aligned. The heating elements 254b1a and 254b1b are arranged near each end of the heater substrate 254a in the lateral direction. On the other hand, the heating element 254b2 is arranged in the center of the heater substrate 254a in the lateral direction.

[0074] The shape of the aluminum plates 261 and 262 (not shown), which are heat equalizing members, and their positions on the heater substrate 254a are the same as those of the aluminum plates 161 and 162, which are the heat equalizing members of the second embodiment. That is, the heat equalizing member of this embodiment is composed of two aluminum plates 261 and 262. The driving-side aluminum plate 261 and the non-driving-side aluminum plate 262 are arranged symmetrically with respect to the longitudinal center of the heater 254 of the fixing device 50. A gap is provided between the two aluminum plates 261 and 262 to prevent interference during thermal expansion. The aluminum plates 261 and 262 are each formed with positioning portions 261a and 262a for positioning relative to the heater holder 252 (not shown). The positioning portion 261a of the driving-side aluminum plate 261 extends 5 mm from the driving-side end of the aluminum plate 261 toward the longitudinal center, with a length of 5 mm. Furthermore, the positioning portion 262a of the aluminum plate 262 arranged on the non-drive side is formed with a length of 5 mm from a position 5 mm from the end of the aluminum plate 262 on the non-drive side toward the center in the longitudinal direction.

[0075] [Power Control Unit] Furthermore, the power control circuit of the fixing device 50 of this embodiment is composed of a triac 256a (first switch) and a triac 256b (second switch). One terminal of each of the heating elements 254b1a, 254b1b, and 254b2 is connected to a contact 254d1 via a conductor 254c. The other terminal of each of the heating elements 254b1a and 254b1b (first heating elements) is connected to a contact 254d2 via a conductor 254c. The other terminal of the heating element 254b2 (second heating element) is connected to a contact 254d3 via a conductor 254c.

[0076] A contact 254d1 (first contact) of the heater 254 is connected to a second pole of the AC power supply 55. A contact 254d2 (third contact) of the heater 254 is connected to a triac 256a (first switch) and is connected to a first pole of the AC power supply 55 via the triac 256a. A contact 254d3 (second contact) of the heater 254 is connected to a triac 256b (second switch) and is connected to the first pole of the AC power supply 55 via the triac 256b.

[0077] Next, in this embodiment, the temperature gradient that occurs on the heater substrate 254a when each heating element generates heat upon power supply will be described. In this embodiment, as shown in FIG. 13, the heating element 254b2 is disposed at the center of the heater substrate 254a in the lateral direction. Therefore, when power is supplied to the heating element 254b2, a temperature gradient occurs in which the temperature of the heater substrate 254a is higher in the lateral center and lower toward the lateral ends. Therefore, if the positioning portions 261a and 262a of the aluminum plates 261 and 262 are disposed in the longitudinal region where the heating element 254b2 is disposed, the thermal capacity of the positioning portions 261a and 262a enhances the temperature gradient in the lateral direction of the heater substrate 254a. Furthermore, a large temperature gradient results in distortion due to uneven thermal expansion of the heater substrate 254a, resulting in significant deformation of the heater substrate 254a. In other words, not only the heating elements arranged asymmetrically in the short direction of the heater substrate 254a, but also the heating elements arranged symmetrically will have a larger temperature gradient in the heater substrate 254a when heated compared to heating elements arranged at both ends of the short direction of the heater substrate 254a.

[0078] In this embodiment, the longitudinal positions of the positioning portions 261a, 262a of the aluminum plates 261, 262 are such that they do not overlap with the heating element 254b2, which is located in the center of the heater substrate 254a in the lateral direction, via the heater substrate 254a. The positioning portions 261a, 262a are located such that at least a portion of the positioning portions 261a, 262a overlap with the heating element 254b1, which is located symmetrically at the end of the heater substrate 254a in the lateral direction, via the heater substrate 254a. This reduces the thermal gradient that occurs when the heating element generates heat, and suppresses deformation of the heater substrate due to distortion.

[0079] As described above, according to this embodiment, it is possible to suppress deformation of the heater substrate due to the positioning portion of the temperature equalizing member. [Explanation of symbols]

[0080] 52 Heater holder 54 Heater 54a Heater board 54b1, 54b2, 54b3 Heating elements 60 Aluminum Plate 60a Positioning part

Claims

1. A fixing device that fixes an unfixed toner image on a recording material to the recording material, a heater having an elongated substrate and a plurality of heating elements disposed on the substrate; a temperature equalizing member for equalizing the temperature of the substrate; a holder that holds the heater and the temperature equalizing member; Equipped with the heat equalizing member is disposed between the heater and the holder in a thickness direction of the substrate, the temperature equalizing member has a positioning portion that determines a longitudinal position of the temperature equalizing member relative to the holder, The fixing device, wherein the positioning portion is located in a position overlapping a first heat generating element of the plurality of heat generating elements in the longitudinal direction, and outside an area of ​​a second heat generating element of the plurality of heat generating elements.

2. 2. The fixing device according to claim 1, wherein the temperature equalizing member is held by the holder by fitting the positioning portion into a recess provided in the holder.

3. 2. The fixing device according to claim 1, further comprising: a first switch for supplying or cutting off power to the first heating element; and a second switch for supplying or cutting off power to the second heating element.

4. 4. The fixing device according to claim 3, wherein both ends of the heat equalizing member in the longitudinal direction are disposed at substantially the same positions as both ends of the first heat generating element via the substrate.

5. 2. The fixing device according to claim 1, wherein the shape of the first heat generating element is symmetrical with respect to the center of the substrate in the longitudinal direction and the center of the substrate in the lateral direction.

6. the heat-equalizing member includes a first heat-equalizing member and a second heat-equalizing member; 6. The fixing device according to claim 1, wherein the first heat equalizing member is disposed on one end side of the heater in the longitudinal direction, and the second heat equalizing member is disposed on the other end side of the heater in the longitudinal direction.

7. the first heat equalizing member has a first positioning portion, the second heat equalizing member has a second positioning portion, the first positioning portion of the first heat equalizing member is located outside an area corresponding to the first heat generating element and a third heat generating element having a length in the longitudinal direction shorter than that of the second heat generating element when viewed in the short-side direction of the substrate, and at least a portion of the first positioning portion is located within an area corresponding to the first heat generating element; 7. The fixing device according to claim 6, wherein the second positioning portion of the second heat equalizing member is located outside the area corresponding to the third heat generating element when viewed in the short-side direction, and at least a portion of the second positioning portion is located within the area corresponding to the first heat generating element.

8. 8. The fixing device according to claim 1, wherein the positioning portion is formed by bending the heat equalizing member.

9. an image forming means for forming an unfixed toner image on a recording material; a fixing device according to any one of claims 1 to 8, which fixes an unfixed toner image on a recording material; An image forming apparatus comprising:

10. the fixing device, a cylindrical film heated by the heater; a pressure roller that forms a nip portion with the film; and 10. The image forming apparatus according to claim 9, wherein the heater is disposed in the internal space of the film, the film is sandwiched between the heater and the pressure roller, and the image on the recording material is heated through the film at the nip portion.

Images