Heating device, image forming device

Abstract

To prevent deformation of a nip forming member and a holding member.SOLUTION: A fixing device 9 comprises: an endless fixing belt 20; a pressure roller 21 that is opposite to the fixing belt 20; a heater 22; a heater holder 23 that is provided inside the fixing belt 20 and holds the heater 22; and a stay 24 that supports the heater holder 23 from the opposite side of the pressure roller 21. The heater 22 has a plurality of heater positioning parts 23b1, 23b2, 23b3 that determine a position of the heater 22 with respect to the heater holder 23 in a direction of rotation of the fixing belt 20. The heater holder 23 has a heater holder positioning part 23c that determines a position of the heater holder 23 with respect to the stay 24 in the direction of rotation of the fixing belt 20, and in a longitudinal direction, the heater holder positioning part 23c is arranged closer to a center position M1 than at least either one of the first heater positioning part 23b1 or the second heater positioning part 23b2.SELECTED DRAWING: Figure 12

Description

[Technical field]

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

[0002] In a fixing device as a heating device, a nip forming member provided on the inside of a fixing belt (belt member) contacts a pressure roller (opposing member) through the fixing belt to form a fixing nip between the fixing belt and the pressure roller. The nip forming member is held by a holding member from the opposite side of the fixing belt.

[0003] In such a fixing device, the fixing belt rotates in response to the rotation of the pressure roller. The rotation of the fixing belt causes a force in the rotation direction on the nip forming member that contacts the inside of the fixing belt. This causes a problem of deformation such as bending of the nip forming member. In particular, in a configuration in which the nip forming member is positioned relative to the holding member at two points on both sides in the longitudinal direction, there is a problem of the center side of the nip forming member that is not positioned bending toward the downstream side in the rotation direction.

[0004] In Patent Document 1 (JP 2002-72719 A), a heater is held in a recess of a stay holder. On the upstream side of the recess of the stay holder, abutment portions are provided on both ends, and a deformation prevention portion is provided between the abutment portions.

[0005] As disclosed in Patent Document 1, by providing a third contact portion between the two contact portions at both ends, deformation of the nip forming member can be suppressed.

[0006] However, when the nip forming member is positioned by a positioning portion provided on the holding member, a pressure force is generated on the holding member toward the downstream side in the rotation direction of the fixing belt, causing the holding member to bend toward the downstream side. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to suppress deformation of the nip forming member and the holding member. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a heating device comprising an endless belt member, an opposing member opposing the belt member, a heating member, a nip forming member provided inside the belt member and forming a nip portion between the belt member and the opposing member, a holding member that holds the nip forming member, and a support member that supports the holding member from the opposite side to the opposing member side, wherein the heating member and the nip forming member are the same member or different members, and when a center position of a heating area in a longitudinal direction of the heating member is taken as a center position in the longitudinal direction, at least one of the nip forming member or the holding member has a plurality of nip forming member positioning portions, and the nip forming member is positioned by abutting against the holding member in a direction from the upstream side to the downstream side in a rotation direction of the belt member at the nip forming member positioning portions, and the nip forming member positioning portions are provided on one side and the other side of the center position in the longitudinal direction. a first nip forming member positioning portion and a second nip forming member positioning portion disposed respectively, and a third nip forming member positioning portion disposed closer to the central position than the first nip forming member positioning portion and the second nip forming member positioning portion, at least one of the holding member and the support member has a holding member positioning portion, the holding member abuts against the support member in a direction from the upstream side to the downstream side in the rotation direction of the belt member at the holding member positioning portion, and the holding member is positioned, and in the longitudinal direction, the holding member positioning portion is disposed closer to the central position than at least one of the first nip forming member positioning portion and the second nip forming member positioning portion. The heating member and the nip forming member are the same member, the heating member is made of one or more resistive heating elements and includes a central heating portion and an end heating portion which can be energized independently, the central heating portion is provided at a position closer to the center position in the longitudinal direction than the end heating portions, and at least one of the nip forming member positioning portion and the holding member positioning portion is provided at a position in the longitudinal direction outside the central heating portion, outside an area through which a recording medium with the largest width passes among recording media to which the central heating portion corresponds, and corresponding to an area through which a recording medium one width wider than the recording medium passes. It is characterized by: Effect of the Invention

[0009] According to the heating device of the present invention, deformation of the nip formation member and the holding member can be suppressed. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of an image forming apparatus. [Diagram 2] FIG. 2 is a schematic diagram of a fixing device. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. 13 is a diagram showing a state in which a connector is attached to a heater and a heater holder. [Figure 10] 10A and 10B are diagrams showing a configuration of a positioning part different from that of the present embodiment, in which FIG. 10A is a plan view showing a state in which a heater is not deformed, and FIG. 10B is a plan view showing a state in which a heater is deformed. [Figure 11] FIG. 11 is a side cross-sectional view showing the displacement of the heater. [Figure 12] 1A and 1B are diagrams showing the configuration of the positioning part of this embodiment, in which (a) is a plan view showing the heater positioning part, (b) is a plan view showing the holder positioning part, and (c) is a diagram showing the longitudinal distribution of the deflection amount in the short side direction of the heater holder. [Figure 13] 10A and 10B are diagrams illustrating the configuration of a positioning portion according to a second embodiment of the present invention, in which FIG. 10A is a plan view illustrating a heater positioning portion, and FIG. 10B is a plan view illustrating a holder positioning portion. [Figure 14] 13A and 13B are diagrams illustrating the configuration of a positioning portion according to a third embodiment of the present invention, in which FIG. 13A is a plan view showing a heater positioning portion, and FIG. 13B is a plan view showing a holder positioning portion. [Figure 15] FIG. 8 is a plan view showing a heater having a different configuration from that in FIG. 7. [Figure 16] FIG. 8 is a plan view showing a heater having a different configuration from that in FIG. 7. [Figure 17] FIG. 8 is a plan view showing a heater having a different configuration from that in FIG. 7. [Figure 18] FIG. 8 is a plan view showing a heater having a different configuration from that in FIG. 7. [Figure 19] FIG. 13 is a plan view showing a configuration of a positioning portion according to a fourth embodiment of the present invention. [Figure 20] FIG. 13 is a plan view showing a configuration of a positioning portion according to a fifth embodiment of the present invention. [Figure 21] FIG. 13 is a plan view showing a configuration of a positioning portion according to a sixth embodiment of the present invention. [Figure 22] FIG. 13 is a plan view showing a configuration of a positioning portion according to a seventh embodiment of the present invention. [Diagram 23] FIG. 13 is a plan view showing the configuration of a positioning portion according to an eighth embodiment of the present invention. [Figure 24] FIG. 13 is a plan view showing the configuration of a positioning portion according to a ninth embodiment of the present invention. [Diagram 25] FIG. 10 is a side cross-sectional view showing the configuration of a positioning portion according to a tenth embodiment of the present invention. [Figure 26] FIG. 23 is a side cross-sectional view showing the configuration of a positioning portion of an eleventh embodiment of the present invention. [Figure 27] 26A and 26B are diagrams showing the configuration of a positioning section according to a twelfth embodiment of the present invention. [Figure 28] 3 is a schematic diagram showing a fixing device different from that in FIG. 2. [Figure 29] 3 is a schematic diagram showing a fixing device different from that in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and the duplicated description will be appropriately simplified or omitted. Hereinafter, a fixing device provided in an image forming apparatus will be described as a heating device according to one embodiment of the present invention.

[0012] FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.

[0013] The image forming apparatus 100 shown in FIG. 1 includes four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body. The imaging units 1Y, 1M, 1C, and 1Bk have the same configuration except that they contain different color developers, namely, yellow, magenta, cyan, and black. These color developers correspond to the color separation components of a color image. Each imaging unit 1Y, 1M, 1C, and 1Bk includes a drum-shaped photoconductor 2 as an image carrier, a charging device 3, a developing device 4, and a cleaning device 5. The charging device 3 charges the surface of the photoconductor 2. The developing device 4 supplies toner as a developer to the surface of the photoconductor 2 to form a toner image. The cleaning device 5 cleans the surface of the photoconductor 2.

[0014] The image forming apparatus 100 also includes an exposure device 6, a paper feeder 7, a transfer device 8, a fixing device 9, and a paper discharge device 10. The exposure device 6 exposes the surface of each photoconductor 2 to light and forms an electrostatic latent image on the surface. The paper feeder 7 supplies paper P as a recording medium to a paper transport path 14. The transfer device 8 transfers the toner image formed on each photoconductor 2 to the paper P. The fixing device 9 fixes the toner image transferred to the paper P to the surface of the paper P. The paper discharge device 10 discharges the paper P to the outside of the apparatus. The imaging units 1, the photoconductor 2, the charging device 3, the exposure device 6, the transfer device 8, etc. constitute an image forming means for forming an image on paper.

[0015] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body, four primary transfer rollers 12 as primary transfer members, and a secondary transfer roller 13 as a secondary transfer member. The intermediate transfer belt 11 is stretched by a plurality of rollers. The primary transfer rollers 12 transfer the toner images on the photoconductors 2 to the intermediate transfer belt 11. The secondary transfer rollers 13 transfer the toner images transferred onto the intermediate transfer belt 11 to a sheet of paper P. Each of the primary transfer rollers 12 contacts the photoconductors 2 via the intermediate transfer belt 11. As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other, and a primary transfer nip is formed between them. Meanwhile, the secondary transfer roller 13 contacts one of the rollers stretching the intermediate transfer belt 11 via the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0016] Further, a pair of timing rollers 15 is provided on the paper transport path 14 between the paper feeder 7 and the secondary transfer nip (secondary transfer roller 13).

[0017] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0018] When an instruction to start a printing operation is given, in each of the imaging units 1Y, 1M, 1C, and 1Bk, the photoconductor 2 is rotated clockwise in FIG. 1, and the surface of the photoconductor 2 is charged to a uniform high potential by the charging device 3. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the original reading device or the print information instructed to be printed from the terminal. This reduces the potential of the exposed portion, forming an electrostatic latent image. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

[0019] The toner images formed on each photoconductor 2 rotate with the rotation of each photoconductor 2 and reach the primary transfer nip (the position of the primary transfer roller 12). The toner images are transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 1, so as to be superimposed one on the other. The toner images transferred onto the intermediate transfer belt 11 are transported to the secondary transfer nip (the position of the secondary transfer roller 13) with the rotation of the intermediate transfer belt 11. The toner images are transferred to the paper P transported at the secondary transfer nip. This paper P is supplied from the paper feeder 7. The paper P supplied from the paper feeder 7 is stopped once by the timing roller 15, and then transported to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip. Thus, a full-color toner image is carried on the paper P. After the toner image is transferred, the toner remaining on each photoconductor 2 is removed by each cleaning device 5.

[0020] The paper P onto which the toner image has been transferred is transported to a fixing device 9, which fixes the toner image onto the paper P. Thereafter, the paper P is discharged outside the apparatus by a paper discharge device 10, completing a series of printing operations.

[0021] Next, the configuration of the fixing device will be described.

[0022] As shown in FIG. 2, the fixing device 9 according to the present embodiment includes a fixing belt 20 as a belt member or fixing member, a pressure roller 21 as an opposing member or pressure member, a planar heater 22 as a nip forming member or heating member, a heater holder 23 as a holding member, a stay 24 as a supporting member, and a thermistor 38 as a temperature detecting member. The fixing belt 20 is an endless belt member. The pressure roller 21 contacts the outer peripheral surface of the fixing belt 20 to form a fixing nip N as a nip portion. The heater holder 23 holds the heater 22. The stay 24 supports the heater holder 23 from the rear side of the heater holder 23 in the longitudinal direction. The thermistor 38 contacts the rear side of the heater 22 and detects the temperature of the heater 22. 2 (the direction of the double-headed arrow X in FIG. 3) is the longitudinal direction of the fixing device 9, or the fixing belt 20, the pressure roller 21, the heater 22, the heater holder 23, the stay 24, etc., and hereinafter, this direction is simply referred to as the longitudinal direction. Note that this longitudinal direction also corresponds to the width direction of the paper being transported, the belt width direction of the fixing belt 20, and the axial direction of the pressure roller 21.

[0023] The fixing belt 20 has a cylindrical substrate (substrate layer) made of polyimide (PI) having an outer diameter of 25 mm and a thickness of 40 to 120 μm. A release layer made of fluororesin such as PFA or PTFE and having a thickness of 5 to 50 μm is formed on the outermost surface of the fixing belt 20 in order to increase durability and ensure releasability. An elastic layer made of rubber or the like having a thickness of 50 to 500 μm may be provided between the substrate and the release layer. The substrate of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with polyimide, PTFE, or the like as a sliding layer.

[0024] The pressure roller 21 has an outer diameter of, for example, 25 mm, and is composed of a solid iron core 21a, an elastic layer 21b formed on the surface of the core 21a, and a release layer 21c formed on the outside of the elastic layer 21b. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 mm. In order to improve the release property of the surface of the elastic layer 21b, it is desirable to form the release layer 21c made of a fluororesin layer having a thickness of, for example, about 40 μm.

[0025] The heater 22 is disposed so as to be in contact with the inner circumferential surface of the fixing belt 20. The heater 22 in this embodiment comes into contact with the pressure roller 21 via the fixing belt 20 and serves as a nip forming member that forms a fixing nip N between the heater 22 and the pressure roller 21. The fixing belt 20 is a member to be heated by the heater 22.

[0026] The heater 22 may be in non-contact with the fixing belt 20 or indirectly in contact with the fixing belt 20 via a low friction sheet, etc. When the heater 22 is in direct contact with the fixing belt 20, the efficiency of heat transfer to the fixing belt 20 is improved.

[0027] The heater 22 is composed of a substrate 50, a first insulating layer 51, a conductor layer 52 having a resistive heating element 60, a second insulating layer 53, which are stacked in sequence on the fixing nip N side of the substrate 50, and a third insulating layer 54 stacked on the opposite side of the substrate 50.

[0028] The heater holder 23 and the stay 24 are disposed on the inner circumferential side of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends thereof are supported by both side walls of the fixing device 9. The stay 24 supports the surface of the heater holder 23 opposite to the heater 22 side, so that the heater 22 and the heater holder 23 are maintained without being significantly deflected by the pressure force of the pressure roller 21. This allows the fixing nip N to be stably formed between the fixing belt 20 and the pressure roller 21.

[0029] Note that the stay 24 supporting the heater holder 23 means that the stay 24, which has a portion extending in the pressure direction of the pressure roller 21 (left and right direction in the figure) or a portion with thickness, abuts against the heater holder 23 from the side opposite the pressure roller 21 (left side in the figure). This makes it possible to suppress bending of the heater holder 23 due to the pressure force from the pressure roller 21 (particularly bending in the longitudinal direction in this embodiment). However, the above-mentioned abutment is not limited to the case where the stay 24 abuts against the heater holder 23 directly, but also includes the case where the stay 24 abuts against the heater holder 23 via another member. Even in such a case, the stay 24 can suppress bending of the heater holder 23 against the pressure force from the pressure roller 21.

[0030] The heater holder 23 is desirably formed of a heat-resistant material because it is likely to become hot due to the heat of the heater 22. For example, when the heater holder 23 is formed of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, the heat transfer from the heater 22 to the heater holder 23 is suppressed. This allows the heater 22 to heat the fixing belt 20 efficiently.

[0031] The pressure roller 21 and the fixing belt 20 are pressed against each other by a spring as a biasing member. As a result, a fixing nip N is formed between the fixing belt 20 and the pressure roller 21. The pressure roller 21 functions as a drive roller that is rotated by a driving force transmitted from a driving means provided in the image forming apparatus main body 103 (see FIG. 1). Meanwhile, the fixing belt 20 is configured to rotate in accordance with the rotation of the pressure roller 21. When the fixing belt 20 rotates, the fixing belt 20 slides against the heater 22. In order to improve the sliding property of the fixing belt 20, a lubricant such as oil or grease may be interposed between the heater 22 and the fixing belt 20.

[0032] When the printing operation is started, the pressure roller 21 is rotated and the fixing belt 20 starts to rotate. Furthermore, the fixing belt 20 is heated by supplying power to the heater 22. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), the paper P carrying an unfixed toner image is conveyed in the direction of the arrow A (paper conveyance direction) and enters the fixing nip N between the fixing belt 20 and the pressure roller 21, as shown in FIG. 2. As a result, the unfixed toner image on the paper P is heated and pressurized by the fixing nip N, and is fixed to the paper P.

[0033] FIG. 3 is a perspective view of the fixing device, and FIG. 4 is an exploded perspective view thereof.

[0034] As shown in Figs. 3 and 4, the device frame 40 of the fixing device 9 includes a first device frame 25 including a pair of side walls 28 as side plates and a front wall 27, and a second device frame 26 including a rear wall 29. The pair of side walls 28 are disposed at one end and the other end of the fixing belt 20 in the width direction. The two side walls 28 support the pressure roller 21 and flanges 32 provided on both ends of the fixing belt 20. Each side wall 28 is provided with a plurality of engagement protrusions 28a. The engagement protrusions 28a are engaged with engagement holes 29a provided in the rear wall 29, whereby the first device frame 25 and the second device frame 26 are assembled together.

[0035] Each side wall portion 28 has an insertion groove 28b for inserting the rotating shaft of the pressure roller 21. The insertion groove 28b opens on the rear wall portion 29 side and is a butting portion that does not open on the opposite side. A bearing 30 that supports the rotating shaft of the pressure roller 21 is provided at the end on the butting portion side. The pressure roller 21 is rotatably supported by both side wall portions 28 by mounting both ends of the rotating shaft to the bearings 30.

[0036] Further, a drive transmission gear 31 is provided as a drive transmission member on one end side of the rotation shaft of the pressure roller 21. The drive transmission gear 31 is arranged in a state where the pressure roller 21 is supported by both side wall portions 28 and is exposed outside the side wall portions 28. As a result, when the fixing device 9 is mounted on the image forming apparatus main body 103 (see FIG. 1), the drive transmission gear 31 is connected to a gear provided on the image forming apparatus main body 103, and a drive force from a drive source can be transmitted to the pressure roller 21. Note that the drive transmission member that transmits the drive force to the pressure roller 21 may be a pulley that stretches a drive transmission belt or a coupling mechanism, in addition to the drive transmission gear 31.

[0037] At both ends of the fixing belt 20 in the longitudinal direction, flanges 32 are provided as a pair of end holding members for supporting the fixing belt 20 and the like. The flanges 32 are part of the device frame 40 of the fixing device 9. The fixing belt 20 is supported by the flanges 32 in a so-called free belt manner in which no tension is applied in the circumferential direction when the fixing belt 20 is not rotating. Each flange 32 is provided with a guide groove 32a. The flanges 32 are assembled to the sidewall portion 28 by inserting the guide groove 32a along the edge of the insertion groove 28b of the sidewall portion 28.

[0038] In addition, a pair of springs 33 serving as urging members are provided between each flange 32 and the rear wall portion 29. The stays 24 and the flanges 32 are urged toward the pressure roller 21 by each spring 33, so that the fixing belt 20 is pressed against the pressure roller 21. As a result, a fixing nip N is formed between the fixing belt 20 and the pressure roller 21.

[0039] As shown in FIG. 4, a hole 29b is provided as a positioning portion at one end in the longitudinal direction of the rear wall 29 constituting the second device frame 26. The hole 29b is a portion for positioning the fixing device body relative to the image forming device body 103. The image forming device body 103 is provided with a protrusion 101 as a positioning portion. When the fixing device body is attached to the image forming device body 103, the protrusion 101 is inserted into the hole 29b of the fixing device 9, so that the protrusion 101 and the hole 29b fit together, and the fixing device body is positioned in the longitudinal direction relative to the image forming device body 103. Note that no positioning portion is provided at the end opposite to the end where the hole 29b of the rear wall 29 is provided. This prevents the longitudinal expansion and contraction of the fixing device body due to temperature changes from being restricted.

[0040] Fig. 5 is a perspective view of a heater unit consisting of a heater 22, a heater holder 23, and a flange 32, and Fig. 6 is an exploded perspective view thereof. Note that in Figs. 5 and 6, the shape of the heater holder 23 is shown in a simplified form for convenience, and the specific shape will be described later.

[0041] 5 and 6, a rectangular accommodating recess 23a for accommodating the heater 22 is provided on the surface of the heater holder 23 on the fixing belt 20 side (the fixing nip N side). The heater 22 is held in the accommodating recess 23a by being sandwiched together with the heater holder 23 by a connector (described later).

[0042] The pair of flanges 32 have a belt support portion 32b, a belt regulation portion 32c, and a support recess 32d. The belt support portion 32b is a C-shaped portion that is inserted into the inner periphery of the fixing belt 20 to support the fixing belt 20. The belt regulation portion 32c is a flange-shaped portion that contacts an end face of the fixing belt 20 to regulate longitudinal movement (deviation). The heater holder 23 and the stay 24 are inserted into the support recess 32d to support them.

[0043] 5 and 6, a positioning recess 23e is provided as a positioning portion at one end of the heater holder 23 in the longitudinal direction. A fitting portion 32e of a flange 32 shown on the left side of Figs. 5 and 6 fits into this positioning recess 23e, thereby positioning the heater holder 23 and the flange 32 in the longitudinal direction. The flange 32 shown on the right side of Figs. 5 and 6 does not have a fitting portion 32e, and is not positioned in the longitudinal direction relative to the heater holder 23. This prevents the heater holder 23 from expanding and contracting in the longitudinal direction due to temperature changes.

[0044] 4, the flanges 32 are assembled to the side wall portions 28 by inserting the guide grooves 32a into the insertion grooves 28b of the side wall portions 28. Of the two flanges 32 shown in FIG. 4, the flange 32 that is positioned in the longitudinal direction relative to the heater holder 23 is the rear flange 32. The rear flange 32 is assembled to the side wall portions 28, thereby positioning the heater holder 23 in the longitudinal direction relative to the side wall portions 28. In this way, the side wall portions 28 and the flanges 32 function as positioning portions of the fixing device main body that position the heater holder 23 in the longitudinal direction.

[0045] The stay 24 is not positioned in the longitudinal direction relative to the flanges 32. As shown in Fig. 6, the stay 24 is provided at both end sides with step portions 24a that restrict longitudinal movement (falling off) relative to each flange 32, but each step portion 24a is disposed with a longitudinal gap relative to at least one of the flanges 32. In other words, the stay 24 is assembled to both flanges 32 with some play in the longitudinal direction so that longitudinal expansion and contraction due to temperature changes is not restricted, and is not configured to be positioned relative to one of the flanges 32.

[0046] FIG. 7 is a plan view of the heater 22, and FIG. 8 is an exploded perspective view thereof. In the following description, the fixing belt 20 side (fixing nip N side) of the heater 22 is referred to as the "front side", and the heater holder 23 side is referred to as the "back side".

[0047] As shown in FIG. 7 and FIG. 8, the heater 22 is configured by laminating a plurality of constituent layers, including a plate-shaped base material 50, a first insulating layer 51 provided on the front side of the base material 50, a conductor layer 52 provided on the front side of the first insulating layer 51, a second insulating layer 53 covering the front side of the conductor layer 52, and a third insulating layer 54 provided on the back side of the base material 50. The conductor layer 52 is configured by a pair of resistance heating elements 60, a pair of electrode parts 61 as power supply parts, and a plurality of power supply lines 62. The electrode parts 61 are provided on one end side of each resistance heating element 60 in the longitudinal direction. The power supply lines 62 connect between the electrode parts 61 and the resistance heating elements 60 and between the resistance heating elements 60. Also, as shown in FIG. 7, at least a portion of each electrode part 61 is not covered by the second insulating layer 53 and is exposed in order to ensure connection with a connector described later.

[0048] Each resistance heating element 60 can be formed by, for example, applying a paste prepared by mixing silver palladium (AgPd) and glass powder to the substrate 50 by screen printing or the like, and then firing the substrate 50. In addition to these, a resistance material such as silver alloy (AgPt) or ruthenium oxide (RuO2) may be used as the material of the resistance heating element 60. In this embodiment, each resistance heating element 60 is provided so as to extend in parallel with each other in the longitudinal direction of the substrate 50. One end (right end in FIG. 7) of each resistance heating element 60 is electrically connected to each other via a power supply line 62, and the other end (left end in FIG. 7) of each resistance heating element 60 is electrically connected to the electrode portion 61 via a separate power supply line 62. The power supply line 62 is made of a conductor having a resistance value smaller than that of the resistance heating element 60. The power supply line 62 and the electrode portion 61 may be made of a material such as silver (Ag) or silver palladium (AgPd), and the power supply line 62 and the electrode portion 61 are formed by screen printing such a material.

[0049] 7 is the region in which the resistance heating element 60 is provided in the longitudinal direction of the heater 22, and is the main heat generation region of the heater 22. Hereinafter, this region M will be referred to as the heating region M of the heater 22. The center of the heating region M is the central position M1 in the longitudinal direction. The central position M1 is also the central position in the longitudinal direction of the paper P passed through the fixing device 9.

[0050] The substrate 50 is made of a metal material such as stainless steel (SUS), iron, or aluminum. In addition to metal materials, ceramics, glass, and the like can also be used as the material of the substrate 50. When an insulating material such as ceramics is used for the substrate 50, the first insulating layer 51 between the substrate 50 and the conductor layer 52 can be omitted. On the other hand, metal materials are excellent in durability against rapid heating and are easy to process, so they are suitable for reducing costs. Among metal materials, aluminum and copper are particularly preferable in that they have high thermal conductivity and are less likely to cause temperature unevenness. Stainless steel also has the advantage of being cheaper to manufacture than these materials.

[0051] Each of the insulating layers 51, 53, and 54 is made of heat-resistant glass, and may be made of ceramic, polyimide (PI), or the like.

[0052] FIG. 9 is a perspective view showing a state in which a connector 70 serving as a power supply member is attached to the heater 22 and the heater holder 23. As shown in FIG.

[0053] 9, the connector 70 has a resin housing 71 and leaf spring contact terminals 72 fixed to the housing 71. The contact terminals 72 have a pair of contact points 72a that come into contact with the electrode portions 61 of the heater 22. In addition, a power supply harness 73 is connected to the connector 70 (contact terminals 72).

[0054] 9, the connector 70 is attached so as to sandwich the heater 22 and the heater holder 23 from the front and back sides together. As a result, each contact portion 72a of the contact terminal 72 elastically contacts (pressure-welds) with the electrode portion 61 of the heater 22. As a result, the resistance heating element 60 and a power supply unit provided in the image forming apparatus are electrically connected via the connector 70, and power can be supplied from the power supply unit to the resistance heating element 60.

[0055] In the fixing device 9 as described above, the fixing belt 20 is rotated by the rotation of the pressure roller 21, so that the heater 22 and the heater holder 23 in contact with the inside of the fixing belt 20 receive a force in the rotation direction of the fixing belt 20. This causes deformation such as bending (or positional deviation) in the heater 22 and the heater holder 23. This causes the resistance heating element 60 provided in the heater 22, etc. to be displaced from its predetermined position.

[0056] First, the deformation of the heater will be described with reference to FIG. 10. The heater holder 23' shown in FIG. 10 has a different heater positioning portion from the heater holder 23 of this embodiment, which will be described later, but otherwise has the same structure. FIG. 10(a) shows the heater 22 in an undeformed state, and FIG. 10(b) shows the heater 22 in a bent state due to friction with the fixing belt 20. The Y direction indicated by the double-headed arrow in FIG. 10 is the short-side direction of the heater 22, heater holder 23, etc. This short-side direction is a direction that intersects with the longitudinal direction (particularly, a direction perpendicular to the longitudinal direction in this embodiment), and is different from the thickness direction of the heater 22, etc. The short-side direction is also the same as the paper transport direction.

[0057] As shown in Fig. 10(a), the heater holder 23' has a recess 23a recessed toward the side opposite the fixing belt 20 (the rear side of the paper surface of Fig. 10a and the left side of Fig. 2). The heater 22 is attached to this recess 23a, whereby the heater 22 is held by the heater holder 23'. In other words, the heater 22 is sandwiched between the heater holder 23' and the inner surface of the fixing belt 20, whereby the heater 22 is held at a predetermined position within the fixing device 9.

[0058] The recess 23a has a first heater positioning portion 23b1 and a second heater positioning portion 23b2 on both sides in the longitudinal direction downstream of the heater 22 in the paper transport direction (upper left and right sides in FIG. 10a). The heater positioning portions 23b1 and 23b2 are portions of the downstream wall surface portion that forms the recess 23a that partially protrude upstream in the paper transport direction further than the other wall surface portions. Hereinafter, the heater positioning portions 23b1, 23b2, etc. are also referred to as heater positioning portions 23b.

[0059] 10A, which is the same direction as the paper transport direction, from the fixing belt 20. As a result, the heater 22 moves in the direction of the arrow A, and both longitudinal ends of the downstream side of the heater 22 come into contact with the heater positioning portions 23b1 and 23b2. As a result, the heater 22 is positioned in the short direction relative to the heater holder 23'.

[0060] In this way, the positioning of the heater 22 in the short direction relative to the heater holder 23' can be improved by performing the positioning of the heater 22 in the short direction relative to the heater holder 23' in a partial region in the longitudinal direction of the heater holder 23' (i.e., the heater positioning portions 23b1, 23b2). For example, in a configuration in which the heater 22 is abutted against the heater holder 23' from one end to the other end in the longitudinal direction and the heater 22 is positioned in the heater holder 23', it is necessary to ensure dimensional accuracy over the entire abutment surface of the heater holder 23'. However, by partially providing the heater positioning portions 23b1, 23b2 as in this embodiment, it is only necessary to ensure positional accuracy in this portion. Therefore, the positional accuracy of the heater 22 in the heater holder 23' can be improved, and the heater holder 23' can be easily manufactured.

[0061] However, in such a configuration in which positioning is performed only on both longitudinal sides, as shown in FIG. 10(b), when heater 22 receives a force in the direction of arrow A, the longitudinal center portion is deflected (see the dotted line portion in FIG. 10b).

[0062] Fig. 11 is a cross-sectional view taken along line BB in Fig. 10(b), showing a cross-sectional view of a deflected portion of heater 22. Due to the deflection of the central portion of heater 22 in the longitudinal direction, as shown in Fig. 11, heater 22 is displaced downstream (upper side in Fig. 11) with respect to dashed line NA, which is the central position of fixing nip N in the paper transport direction.

[0063] The heater 22 is disposed at a position (left side position in FIG. 11) where the end surface of the heater 22 on the fixing belt 20 side is recessed from the fixing belt 20 as compared with the heater holder 23'. As a result, the heater 22 comes into close contact with the fixing belt 20 at a position close to the center line NA (i.e., the position where the pressure roller 21 is most convex toward the fixing belt 20 and the heater 22 side). On the other hand, the heater 22 is less likely to come into contact with the fixing belt 20 at a position far from the center line NA, that is, at the end side of the heater 22 in the paper conveying direction. As a result, when the heater 22 is disposed at a target position where it is not displaced (position in FIG. 10a), the resistance heating element 60 comes into close contact with the fixing belt 20 at the center side in the paper conveying direction to efficiently heat the fixing belt 20, and at the end side, contact between the corners of the heater 22 and the fixing belt 20 is suppressed, and wear of the fixing belt 20 due to sliding between the corners of the heater 22 and the fixing belt 20 is prevented.

[0064] 10(b), the downstream portion of the resistance heating element 60 moves away from the center line NA and does not contact the fixing belt 20. This causes the downstream portion of the resistance heating element 60 to enter a dry-burning state. This dry-burning causes the heater 22 to overheat, which may result in damage to the heater 22.

[0065] Furthermore, when the heater 22 is displaced downstream, the corner 221 on the upstream side of the heater 22 approaches the center line NA, and the fixing belt 20 is likely to come into contact with the corner 221. This causes the fixing belt 20 to wear out.

[0066] In recent years, the fixing device has become smaller and faster. This has resulted in a relative decrease in the rigidity of the heater 22. In addition, the increase in pressure from the pressure roller 21 to the fixing belt 20 due to the increase in speed has also increased the frictional force generated between the fixing belt 20 and the heater 22. This has made the above problem particularly noticeable.

[0067] The configuration of the fixing device of this embodiment, which solves the above problems, will be described with reference to Fig. 12. Fig. 12(a) is a view of the heater 22 and heater holder 23 as viewed from the fixing nip N side (the right side in Fig. 2), and Fig. 12(b) is a view of the heater holder 23 and stay 24 as viewed from the opposite side to the fixing nip N side (the left side in Fig. 2). The upper side of Fig. 12(a) and Fig. 12(b) is the downstream side in the paper transport direction.

[0068] As shown in FIG. 12(a), the heater holder 23 of this embodiment has a first heater positioning portion (first nip forming member positioning portion) 23b1 and a second heater positioning portion (second nip forming member positioning portion) 23b2 on both sides in the longitudinal direction, and also has a third heater positioning portion (third nip forming member positioning portion) 23b3 on the longitudinal center side. The first heater positioning portion 23b1 is disposed on one side in the longitudinal direction from the center position M1 (see FIG. 7) of the heating region M of the heater 22, and the second heater positioning portion 23b2 is disposed on the other side in the longitudinal direction from the center position M1. The third heater positioning portion 23b3 is provided at a position closer to the center position M1 than the heater positioning portions 23b1 and 23b2. Note that this closer position also includes the case where the heater positioning portion 23b3 is provided at the center position M1.

[0069] The third heater positioning portion 23b3 abuts against the heater 22, thereby suppressing deflection at the center side in the longitudinal direction of the heater 22. That is, deflection (or displacement to the downstream side) of the heater 22 as shown in FIG. 11 can be suppressed. This suppresses the above-mentioned damage and wear of the heater 22. Note that in FIG. 12(a), the wall portion on the upstream side of the recess 23a also has portions protruding toward the heater 22 on both longitudinal end sides.

[0070] By the way, the heater holder 23 is pressed toward the downstream side in the paper conveyance direction by the contact of the heater 22 with the heater positioning portion 23b. This pressure may cause the heater holder 23 to bend toward the downstream side. In particular, when the heater holder 23 is made of a resin material, even if the material is heat-resistant, the rigidity of the heater holder 23 decreases due to the heat generated by the heater 22. For this reason, the heater holder 23 is more likely to bend.

[0071] When the heater holder 23 is deformed downstream in the paper transport direction, the positions at which the heater positioning portions 23b1 to 23b3 position the heater 22 are also shifted downstream accordingly, which may cause the heater 22 to bend (displace).

[0072] 12(b), the heater holder 23 has a first holder positioning portion (first holding member positioning portion) 23c1 and a second holder positioning portion (second holding member positioning portion) 23c2 that position the heater holder 23 with respect to the stay 24. Hereinafter, the holder positioning portions 23c1, 23c2, etc. are also referred to as holder positioning portions 23c.

[0073] The first holder positioning portion 23c1 or the second holder positioning portion 23c2 abuts against the stay 24 from the upstream side in the paper transport direction, and thereby the heater holder 23 is positioned in the paper transport direction with respect to the stay 24. This makes it possible to suppress bending of the heater holder 23 due to pressure being applied to the downstream side in the paper transport direction of the heater 22, and thus to suppress deformation of the heater 22. Therefore, damage and wear of the heater 22 can be suppressed.

[0074] Particularly in this embodiment, the holder positioning parts 23c1 and 23c2 are disposed closer to the center in the longitudinal direction than the heater positioning parts 23b1 and 23b2. Specifically, the holder positioning parts 23c1 and 23c2 are disposed closer to the center position M1 (see FIG. 7) of the heating region M of the heater 22 than the heater positioning parts 23b1 and 23b2. This makes it possible to effectively suppress deflection of the heater holder 23 and the heater 22 at the center in the longitudinal direction. Note that this "close position" also includes the case where the holder positioning parts 23c1 and 23c2 are provided at the center position M1. For example, the holder positioning part 23c1 is closer to the center position M1 than the heater positioning part 23b1 means that the part of the holder positioning part 23c1 closest to the center position M1 is disposed closer to the center position M1 than the heater positioning part 23b1.

[0075] It is not necessary that both of the holder positioning portions 23c1 and 23c2 are disposed closer to the center in the longitudinal direction than the heater positioning portions 23b1 and 23b2. However, by providing the holder positioning portions 23c1 and 23c2 on one and the other longitudinal sides, respectively, and disposing the holder positioning portions 23c1 and 23c2 closer to the center in the longitudinal direction than the heater positioning portions 23b1 and 23b2, respectively, deflection of the heater holder 23 can be effectively suppressed.

[0076] 12(c) is a diagram showing the distribution of the amount of deflection in the longitudinal direction of heater holder 23, where the horizontal axis indicates each position in the longitudinal direction and the vertical axis indicates the amount of deflection (amount of deformation) in the lateral direction of heater holder 23. The solid line in the figure indicates the amount of deflection of heater holder 23 in the fixing device of this embodiment, and the two-dot chain line in the figure indicates the amount of deflection of heater holder 23 in a fixing device of a comparative example, specifically, in a fixing device configured such that stay 24 does not have holder positioning portions 23c1, 23c2.

[0077] 12(c), by positioning the heater holder 23 using the holder positioning parts 23c1 and 23c2, it is possible to reduce the amount of deflection of the heater holder 23, particularly at the positions of the holder positioning parts 23c1 and 23c2 in the longitudinal direction and around them. In particular, by arranging the holder positioning parts 23c1 and 23c2 closer to the longitudinal center than the heater positioning parts 23b1 and 23b2, it is possible to effectively suppress the deflection of the heater holder 23 at the longitudinal center, which is the part where the amount of deflection is large.

[0078] Additionally, the longitudinal widths E11, E12, and E13 of the heater positioning portion 23b are greater than the longitudinal widths E21 and E22 of the holder positioning portion 23c. The heater 22 has a small thickness, and the depth of the recess 23a is also small. Therefore, in order to ensure the strength of the heater positioning portion 23b, it is preferable that the longitudinal widths E11, E12, and E13 are large. However, it is not necessarily required that the longitudinal widths of all the heater positioning portions 23b are greater than the longitudinal widths of all the holder positioning portions 23c.

[0079] Conversely, the longitudinal widths E11, E12, E13 of the heater positioning portions 23b can be made smaller than the longitudinal widths E21, E22 of the holder positioning portions 23c. By making the longitudinal widths E11, E12, E13 of the heater positioning portions 23b smaller, the amount of heat transferred from the heater 22 to the heater holder 23 is suppressed, and the heater 22 can efficiently heat the fixing belt 20. However, it is not necessarily required that the longitudinal widths of all the heater positioning portions 23b are made smaller than the longitudinal widths of all the holder positioning portions 23c.

[0080] As shown in Fig. 12(b), by providing holder positioning portions 23c on one side and the other side in the longitudinal direction (more specifically, on one side and the other side of center position M1 in Fig. 7), heater holder 23 can be positioned with respect to stay 24 on both sides in the longitudinal direction, and the attitude of heater holder 23 is stabilized. However, the configuration of holder positioning portion 23c is not limited to this. For example, only a single holder positioning portion 23c may be provided from one side to the other side in the longitudinal direction.

[0081] 12(a) and 12(b), heater positioning portion 23b and holder positioning portion 23c are provided symmetrically with respect to center position M1 (see FIG. 7) of heating region M of heater 22. This allows heater 22 or heater holder 23 to be positioned evenly on one side and the other side in the longitudinal direction.

[0082] In addition, the fixing belt 20 of this embodiment has a polyimide base. This makes the fixing belt 20 more flexible than a fixing belt having a metal base. Therefore, even if the heater 22 is displaced in the short-side direction relative to the fixing belt 20 as shown in FIG. 11, the fixing belt 20 is more likely to come into contact with the heater 22, and dry-burning of the heater 22 can be suppressed. Therefore, by combining this with the configuration of the positioning unit of this embodiment, dry-burning of the heater 22 can be more reliably prevented. Conversely, in the case where the fixing belt 20 has a metal base, the fixing belt 20 and the heater 22 are more likely to be out of contact with each other when the heater 22 is displaced in the short-side direction, and dry-burning of the heater 22 is more likely to occur. Therefore, it is preferable to apply the configuration of the positioning unit.

[0083] The fixing belt 20 of this embodiment is a rubberless belt that does not have an elastic layer. This makes the fixing belt 20 more flexible than a fixing belt having an elastic layer. Therefore, even if the heater 22 is displaced in the short direction relative to the fixing belt 20 as shown in FIG. 11, the fixing belt 20 is more likely to come into contact with the heater 22, and dry heating of the heater 22 can be suppressed. Therefore, by combining this with the configuration of the positioning unit of this embodiment, dry heating of the heater 22 can be more reliably prevented. Specifically, the fixing belt 20 is made of a cylindrical body and a release layer that forms the outer circumferential surface as described above.

[0084] Furthermore, in a configuration as in this embodiment, in which the heater holder 23 is formed from a resin material and the stay 24 is formed from a material having greater rigidity than the heater holder 23 (a metal material in this embodiment), the heat transfer from the heater 22 to the heater holder 23 is suppressed to improve the energy saving performance of the fixing device 9, while the heater holder 23 and the heater 22 are supported by the highly rigid stay 24, thereby improving the positional accuracy of the heater 22.

[0085] Next, examples of modifications and arrangements of the heater positioning portion and the holder positioning portion will be described.

[0086] As shown in FIGS. 13(a) and 13(b), in this embodiment, the heater holder 23 has a third holder positioning portion 23c3 on the longitudinal center side in addition to a first holder positioning portion 23c1 and a second holder positioning portion 23c2.

[0087] In the longitudinal direction, the third holder positioning portion 23c3 partially overlaps with the third heater positioning portion 23b3. The position where the heater positioning portion 23b in the longitudinal direction is provided is a position where the heater holder 23 is particularly likely to deform when pressure is applied from the heater 22. Therefore, by providing the holder positioning portion 23c at this position, deformation of the heater holder 23 can be effectively suppressed, and therefore deformation of the heater 22 can be effectively suppressed.

[0088] 13, the third holder positioning portion 23c3 overlaps with the third heater positioning portion 23b3, but the longitudinal positions of the other positioning portions may overlap with each other. In this case as well, deformation of the heater holder 23 can be effectively suppressed.

[0089] Moreover, it is preferable to dispose heater positioning portion 23b (particularly third heater positioning portion 23b3 in this embodiment) or holder positioning portion 23c (particularly third holder positioning portion 23c3 in this embodiment) at central position M1 (see FIG. 7) of heat generating region M of heater 22. This makes it possible to position heater 22 or heater holder 23 at a position where deflection of heater 22 or heater holder 23 is most likely to occur, and deflection of heater 22 or heater holder 23 can be effectively suppressed.

[0090] 14(a) and 14(b), the longitudinal center position of the third holder positioning portion 23c3 and the longitudinal center position of the third heater positioning portion 23b3 coincide (see the dotted line in FIG. 14). This makes it possible to effectively suppress deformation of the heater holder 23 in particular. Furthermore, it is preferable that the longitudinal center positions of the third holder positioning portion 23c3 and the third heater positioning portion 23b3 coincide with the central position M1.

[0091] The configuration of the positioning portion of this embodiment is suitable for application to a fixing device 9 that has a component that conducts electricity in the short side direction and is equipped with a resistance heating element 60 that has PTC characteristics.

[0092] The PTC characteristic is a characteristic in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). Since the resistance heating element 60 has the PTC characteristic, the output of the heater 22 increases at low temperatures, and the temperature of the fixing belt 20 can be increased quickly. In addition, since the output of the heater 22 decreases at high temperatures, excessive temperature increase of the heater 22 and fixing belt 20 in non-paper passing areas, such as when small size paper is continuously printed, can be suppressed.

[0093] However, in the case where the resistance heating element 60 has the PTC characteristic and has a component that conducts electricity in the short side direction, when the heater 22 is displaced in the short side direction as shown in FIG. 11, the resistance heating element 60 having the PTC characteristic has a negative effect on the excessive temperature rise of the heater 22. In other words, when only a part of the paper conveying direction (only the upper resistance heating element 60 in FIG. 11) is out of contact with the fixing belt 20, the temperature of the resistance heating element 60 rises in this part, and the resistance value increases. However, when electricity is applied to the resistance heating element 60 in the short side direction (the vertical direction in FIG. 11), the resistance value does not change significantly in the upstream part of the resistance heating element 60, so the current value flowing through the resistance heating element 60 does not change significantly either. And since the amount of heat generated by the resistance heating element 60 is proportional to the square of the current value and the resistance value, if the current value remains almost the same and only the resistance value increases, the amount of heat generated by the resistance heating element 60 increases due to the increase in the resistance value.

[0094] An example of the configuration of a heater 22 having such a resistance heating element 60 is shown in Fig. 15. The resistance heating element 60 provided in the heater 22 in Fig. 15 has PTC characteristics. The current flowing through this resistance heating element 60 has a component Iy that flows in the short side direction. In such a heater 22, excessive temperature rise is likely to occur when the heater 22 is bent and displaced as described above, so it is particularly preferable to suppress deformation of the heater 22 by the configuration of the positioning part of this embodiment.

[0095] Next, a case where the above-mentioned configuration of the positioning portion is applied to a heater 22 having a different form from that shown in FIG. 7 will be described.

[0096] As shown in FIG. 16, in the heater 22, a plurality of (four in FIG. 16) divided resistance heating elements 60 are connected in parallel in the longitudinal direction. A divided region C between the resistance heating elements 60 is provided between each pair of the resistance heating elements 60. The divided region C is a portion in which the area occupied by the resistance heating elements 60 in the longitudinal direction of the heater 22 is small (or the resistance heating elements 60 are not arranged), and is a region in which the amount of heat generated by the heater 22 is small. For example, as shown in FIG. 17, even in the heater 22 having a rectangular resistance heating element 60, the amount of heat generated is small in the divided region C between the resistance heating elements 60. In the heater 22 in FIG. 16, the heat generating region M is a range in which the resistance heating elements 60 are provided in the longitudinal direction, including the divided region C. The divided region C is a longitudinal region including the entire portion in which the resistance heating elements 60 are divided in the longitudinal direction.

[0097] Each resistance heating element 60 in Fig. 16 can be made to have a PTC characteristic. As a result, when a small size paper is passed through, if the temperature of the resistance heating element 60 corresponding to the non-paper passing area rises, the resistance value of the resistance heating element 60 increases, and the amount of heat generated by only the resistance heating element 60 corresponding to the non-paper passing area can be suppressed. Therefore, excessive temperature rise in the non-paper passing areas of the heater 22 and the fixing belt 20 can be suppressed.

[0098] As shown in FIG. 18, the heater 22 may have a configuration having a plurality of heating parts 65A, 65B made up of resistance heating elements 60. Of the plurality of resistance heating elements 60 arranged in the longitudinal direction of the substrate 50, a central heating part 65A made up of the resistance heating elements 60 other than those at both ends and an end heating part 65B made up of the resistance heating elements 60 at both ends are configured to be capable of independently controlling heat generation. Specifically, each of the resistance heating elements 60 other than those at both ends constituting the central heating part 65A is connected to a first electrode part 61A provided on one end side in the longitudinal direction of the substrate 50 via a first power supply line 62A. Also, each of the resistance heating elements 60 constituting the central heating part 65A is connected to a second electrode part 61B provided on the end side opposite to the first electrode part 61A via a second power supply line 62B. On the other hand, each of the resistance heating elements 60 on both ends constituting the end side heating portion 65B is connected via a third power supply line 62C or a fourth power supply line 62D to a third electrode portion 61C (different from the first electrode portion 61A) provided on one end side in the longitudinal direction of the substrate 50. Also, each of these resistance heating elements 60 on both ends is connected to the second electrode portion 61B via a second power supply line 62B, similar to each of the resistance heating elements 60 in the center side heating portion 65A.

[0099] When a voltage is applied to the first electrode portion 61A and the second electrode portion 61B, the resistive heating elements 60 other than those at both ends are energized, and only the central heating portion 65A generates heat. On the other hand, when a voltage is applied to the second electrode portion 61B and the third electrode portion 61C, the resistive heating elements 60 at both ends are energized, and only the end heating portion 65B generates heat. Also, when a voltage is applied to all the electrodes 61A to 61C, it is possible to make both (all) the resistive heating elements 60 at the central heating portion 65A and the end heating portion 65B generate heat. For example, when a relatively small width paper of A4 size (paper passing width: 210 mm) or less is passed through, only the central heating portion 65A generates heat, and when a relatively large width paper of more than A4 size (paper passing width: 210 mm) is passed through, the end heating portion 65B as well as the central heating portion 65A generates heat, so that the heating area corresponds to the paper width.

[0100] In such a heater 22, too, the amount of heat generated is small in the divided region C between the resistance heating elements 60. Note that, although Fig. 18 illustrates only the divided region C between the left end of the figure and the adjacent resistance heating element 60, in reality, divided regions C are formed between all of the resistance heating elements 60.

[0101] In the heater 22 in which the resistance heating element 60 is divided into a plurality of parts in the longitudinal direction, the positioning portion can be provided at a position corresponding to the division region C in the longitudinal direction. Specifically, for example, as shown in FIG. 19, the heater positioning portion 23b3 is arranged in the longitudinal direction corresponding to the division region C. The division region C is a portion in which the amount of heat generated by the heater 22 is small and the amount of deformation due to thermal expansion of the heater 22 and the heater holder 23 is small. Therefore, by arranging the heater positioning portion 23b3 in correspondence with the division region C, the heater positioning portion 23b3 can position the heater 22 in the lateral direction with high precision. In addition, not limited to the heater positioning portion 23b, the holder positioning portion 23c may be arranged in correspondence with the division region C. This allows the heater holder 23 to be positioned in the lateral direction with high precision, and therefore the heater 22 to be positioned in the lateral direction with high precision.

[0102] Conversely, in the heater 22 in which the resistance heating element 60 is divided into a plurality of parts in the longitudinal direction, the positioning portion can be provided at a position outside the longitudinal division region C. For example, as shown in FIG. 20, the heater positioning portions 23b1, 23b2, and 23b3 are provided outside the longitudinal division region C. At the positions where the heater positioning portions 23b1, 23b2, and 23b3 abut against the heater 22, the heat of the heater 22 flows to the heater holder 23, and the temperature of the heater 22 decreases. Therefore, by providing the heater positioning portions 23b1, 23b2, and 23b3 to avoid the positions of the division region C where the heat generation amount is small, the temperature of the heater 22 and the fixing belt 20 can be made uniform in the longitudinal direction, as compared with the configuration in which the positioning portion is provided corresponding to the division region C as shown in FIG. 19. Also, instead of the heater positioning portion 23b, the holder positioning portion 23c may be provided outside the longitudinal division region C. Even at the position where the holder positioning portion 23c abuts against the heater holder 23, the heat of the heater holder 23 flows toward the stay 24. As a result, the heat of the heater 22 is also easily absorbed by the heater holder 23 at this position in the longitudinal direction. Therefore, by arranging the holder positioning portion 23c on the outside of the longitudinal division region C, the temperature of the heater holder 23, and therefore the heater 22 and fixing belt 20 can be made uniform in the longitudinal direction.

[0103] 18, when a sheet of paper P having a width different from the range of each of the heat generating parts 65A, 65B is passed through the fixing device 9, a part of the heat generating area of ​​the heater 22 becomes a non-paper passing area. In the non-paper passing area, the heat is not absorbed by the sheet of paper P, so the temperature of the heater 22 is likely to be high, and the heater 22 and the heater holder 23 are likely to thermally expand compared to the paper passing area. Therefore, by arranging the positioning part to avoid this non-paper passing area, the heater 22 and the heater holder 23 can be accurately positioned in the short side direction.

[0104] 21, for example, the heater 22 is provided with a central heat generating portion 65A with a longitudinal width corresponding to the paper P2 (e.g., A4 paper: 210 mm). The third heater positioning portion 23b3 provided on the heater holder 23 is provided within the paper passing area D1 of the paper P1 with the smallest width that is passed through the fixing device 9. This allows the third heater positioning portion 23b3 to be disposed within the paper passing area in the longitudinal direction regardless of the type of paper passed through the fixing device 9. Therefore, the heater 22 can be positioned in a portion with small thermal expansion, and the heater 22 can be positioned with high accuracy in the short side direction.

[0105] The heater holder 23 is also provided with a fourth heater positioning portion 23b4. The fourth heater positioning portion 23b4 is provided in the longitudinal direction outside the paper passage area D2 of the paper P2 (i.e. outside the area of ​​the center heat generating portion 65A) and within the paper passage area D3 of the paper P3 (e.g. B4 paper: paper width 257 mm) that is one width larger than the paper P2. This allows the fourth heater positioning portion 23b4 to be located within the paper passage area when the end side heat generating portion 65B generates heat. Therefore, the heater 22 can be positioned in a portion with small thermal expansion, and the heater 22 can be positioned with high accuracy in the short direction.

[0106] Moreover, holder positioning portion 23c may be disposed like third heater positioning portion 23b3 or fourth heater positioning portion 23b4 in Fig. 21. This allows heater holder 23 to be positioned with high accuracy in the short side direction, and therefore heater 22 to be positioned with high accuracy in the short side direction.

[0107] The positioning portion can also be provided at a position corresponding to the non-paper passing region in the longitudinal direction. For example, as shown in FIG. 22, the longitudinal heat generating region of the center side heat generating portion 65A and the end side heat generating portion 65B is provided with a width of 300 mm, which is slightly larger than the maximum width of the paper P4 (for example, A3 paper: paper width 297 mm) that is passed through the fixing device 9. The fourth heater positioning portion 23b4 is provided outside the paper passing region D3 of the paper P3, which is one width smaller than the paper P4, within the paper passing region D4 of the paper P4. In other words, the fourth heater positioning portion 23b4 is provided at a position corresponding to the non-paper passing region when the paper P4 is passed. This allows the heater holder 23 to abut against the heater 22 in the region where the temperature of the heater 22 is likely to increase. Therefore, the temperature of the heater 22 and the fixing belt 20 can be uniformed in the longitudinal direction.

[0108] Moreover, the holder positioning portion 23c may be disposed as in the fourth heater positioning portion 23b4 of Fig. 22. This allows the heater holder 23 to be positioned accurately in the short side direction, and the temperatures of the heater holder 23, and therefore the heater 22 and the fixing belt 20, can be made uniform in the long side direction.

[0109] Also, the heater positioning portion 23b can be provided at a position corresponding to the electrode portion 61 of the heater 22. Specifically, as shown in Fig. 23, the fourth heater positioning portion 23b4 is provided at a position corresponding to the electrode portion 61 in the longitudinal direction. This allows the heater 22 to be positioned in the lateral direction with high accuracy at the position where the electrode portion 61 is provided. This makes it possible to improve the positional accuracy between the electrode portion 61 and the contact portion 72a of the contact terminal 72 of the connector 70 (see Fig. 9), thereby preventing power supply failure due to misalignment between them.

[0110] 24, a thermistor 38 and a thermostat 39 as a temperature detection member can be disposed at a position corresponding to the positioning portion 23b in the longitudinal direction. In this embodiment, the thermistor 38 is provided at a position corresponding to the third heater positioning portion 23b3, and the thermostat 39 is provided at a position corresponding to the fourth heater positioning portion 23b4 in the longitudinal direction. However, this is not limited to this.

[0111] The thermostat 39 is a power cut-off member that detects an abnormal rise in temperature of the heater 22 and cuts off power to the heater 22. When the temperature detected by the thermostat 39 exceeds a predetermined threshold value, power to the heater 22 is cut off.

[0112] By arranging the thermistor 38 or the thermostat 39 at a position corresponding to the positioning portion 23b, it is possible to improve the positional accuracy of the thermistor 38 or the thermostat 39 and the heater 22. Therefore, the thermistor 38 or the thermostat 39 can detect the temperature of the heater 22 more accurately.

[0113] 12 and other drawings show a case where the holder positioning portion 23c positions the heater holder 23 upstream of the heater 22 in the paper transport direction, but it may be positioned downstream in the paper transport direction. For example, as shown in FIG. 25, the heater holder 23 is provided with the holder positioning portion 23c. The holder positioning portion 23c abuts against the downstream portion of the stay 24 (the portion downstream of the heater 22) from the upstream side (from the lower side in FIG. 25). This positions the heater holder 23 with respect to the stay 24.

[0114] As described above, the heater 22 comes into contact with the heater positioning portion 23b of the heater holder 23, which pushes the heater holder 23 downstream in the paper transport direction. Therefore, by positioning the heater holder 23 with respect to the stay 24 at a position downstream of the heater 22 in the paper transport direction, it is possible to improve the positional accuracy of the heater 22 and the heater holder 23 in the short side direction (paper transport direction).

[0115] 26, the flange 32 may have a stay positioning portion (support member positioning portion) 32f that the stay 24 abuts against to position the stay 24 in the short-side direction. The stay positioning portion 32f is formed of a flat portion. The stay positioning portion 32f abuts against the stay 24 downstream of the heater 22 in the paper transport direction to position the stay 24. This allows the stay 24 to be positioned relative to the flange 32 downstream of the heater 22, thereby improving the positional accuracy of the stay 24, and therefore the heater holder 23 and heater 22, in the short-side direction.

[0116] 4, the flange 32 is configured to have the guide groove 32a enter the insertion groove 28b of the side wall portion 28. That is, as shown in FIG. 27, the lower wall surface portion 32g forming the guide groove 32a on the downstream side in the paper transport direction abuts against the upper surface of the wall surface portion forming the insertion groove 28b, thereby positioning the flange 32 in the short side direction relative to the side wall portion 28. The abutment position of this wall surface portion 32g against the wall surface portion forming the insertion groove 28b is provided downstream of the heater 22 in the paper transport direction. This makes it possible to improve the positional accuracy in the short side direction of the flange 32, and therefore of the heater holder 23 and the heater 22.

[0117] Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0118] The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0119] Examples of recording media include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic film, prepreg, copper foil, and the like.

[0120] In the above fixing device 9, the heater 22 is the same member as the nip forming member, but the fixing device (heating device) of the present invention is not limited to this. In other words, the fixing device may have a heating member and a nip forming member as different members.

[0121] 28, for example, the fixing device 9 of the present embodiment has a halogen heater 43 in addition to a nip forming member 41 that contacts the inner surface of the fixing belt 20. The fixing device 9 also has a fixing pad 42 as a holding member. Note that a reflective member may be provided between the halogen heater 43 and the stay 24.

[0122] The nip forming member 41 forms a fixing nip N between the pressure roller 21 and the fixing belt 20 .

[0123] Nip forming member 41 also functions as a heat equalizing plate that equalizes the temperature of fixing belt 20 in the longitudinal direction. Nip forming member 41 is made of a material having a higher thermal conductivity than fixing pad 42. Materials that can be used for nip forming member 41 include aluminum, SUS, and copper-based materials.

[0124] Next, a method for calculating the thermal conductivity will be described. When calculating the thermal conductivity, first, the thermal diffusivity of the object is measured, and then the thermal conductivity is calculated using the measured thermal diffusivity.

[0125] The thermal diffusivity was measured using a thermal diffusivity / thermal conductivity measuring device (product name: ai-Phase Mobile 1u, ai-Phase Corporation).

[0126] In order to convert the thermal diffusivity to thermal conductivity, the values ​​of density and specific heat capacity are necessary. A dry automatic density meter (product name: Accupyc 1330, manufactured by Shimadzu Corporation) was used to measure the density. A differential scanning calorimeter (product name: DSC-60, manufactured by Shimadzu Corporation) was used to measure the specific heat capacity, and sapphire was used as a reference material with a known specific heat capacity. In this embodiment, the specific heat capacity was measured five times, and the average value at 50°C was used. If the density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be obtained from the thermal diffusivity α obtained by the thermal diffusivity measurement by the following formula 1.

[0127]

number

[0128] The fixing pad 42 holds the nip forming member 41. The stay 24 supports the fixing pad 42 from the rear side (the side opposite to the fixing nip N).

[0129] The halogen heater 43 heats the inner surface of the fixing belt 20 by radiant heat. The halogen heater 43 has a densely wound portion and an openly wound portion in which the filament is densely wound in the longitudinal direction. The heat generating region M (see FIG. 7) of the halogen heater 43 is the main heat generating region of the halogen heater 43, and is a region including the entire densely wound portion (when the densely wound portions are provided intermittently in the longitudinal direction, the region including the spaces between them).

[0130] Fixing belt 20 is rotated in the direction of the arrow in Fig. 28 by the rotation of pressure roller 21. As a result, like heater 22 and heater holder 23 described above, nip forming member 41 and fixing pad 42 are subjected to a frictional force in the rotational direction of fixing belt 20 and are deflected. Therefore, by applying the configuration of the positioning portion described above to nip forming member 41 and fixing pad 42, that is, by providing fixing pad 42 with a nip forming member positioning portion that positions nip forming member 41 and a holding member positioning portion that positions fixing pad 42 with respect to stay 24, it is possible to suppress deformation of fixing pad 42 due to the frictional force of fixing belt 20, and therefore deformation of nip forming member 41 can be suppressed.

[0131] 29 has a fixing roller 44 and a pressure belt 45 instead of the fixing belt 20 and the pressure roller 21. A halogen heater 43 is provided inside the fixing roller 44. A nip forming member 41, a fixing pad 42, a stay 24, etc. are provided inside the pressure belt 45.

[0132] The halogen heater 43 heats the fixing roller 44 from its inside. The nip forming member 41 forms a fixing nip N between the fixing roller 44 and the nip forming member 41 via the pressure belt 45. The fixing pad 42 holds the nip forming member 41. The stay 24 supports the fixing pad 42 from the rear side (the side opposite to the fixing nip N).

[0133] 29, nip formation member 41 and fixing pad 42 are deformed by the frictional force in the rotational direction of pressure belt 45. Therefore, by applying the configuration of the positioning portion described above to nip formation member 41, deformation of fixing pad 42 due to the frictional force of pressure belt 45 can be suppressed, and deformation of nip formation member 41 can be suppressed.

[0134] Furthermore, the present invention is not limited to the fixing device described in the above embodiment, but can also be applied to a drying device that dries ink applied to paper, and further to a heating device such as a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, or a heat sealer that thermocompresses the seal portion of a packaging material, thereby making it possible to suppress deformation of the holding member or nip forming member (or heating member).

[0135] In the above description, a nip forming member positioning portion for positioning the nip forming member (heater 22 or nip forming member 41) relative to the holding member is provided on the holding member, but it may be provided on the nip forming member side. For example, in the embodiment shown in Fig. 12(a), a heater positioning portion that protrudes toward the heater holder 23 side (upper side in Fig. 12a) may be provided on a part of the longitudinal direction on the downstream side of the short side of the heater 22 (base material 50 thereof).

[0136] In the above embodiment, the holding member positioning portion for positioning the holding member (heater holder 23 or fixing pad 42) with respect to the stay 24 is provided on the holding member, but may be provided on the stay 24 side.

[0137] In the above embodiment, for example, the left side in FIG. 7 is one side in the longitudinal direction, and the right side in FIG. 7 is the other side in the longitudinal direction, but this may be reversed. [Explanation of symbols]

[0138] 1. Image forming device 9 Fixing device (heating device) 20 Fixing belt (belt member or fixing member) 21 Pressure roller (opposing member or pressure member) 22 Heater (nip forming member or heating member) 23 Heater holder (holding member) 23b1 First heater positioning portion (first nip forming member positioning portion) 23b2 Second heater positioning portion (second nip forming member positioning portion) 23b3 Third heater positioning portion (third nip forming member positioning portion) 23b4 Fourth heater positioning portion (fourth nip forming member positioning portion) 23c1 First holder positioning portion (holding member positioning portion) 23c2 Second holder positioning portion (holding member positioning portion) 23c3 Third holder positioning portion (holding member positioning portion) 24 Stay (support member) 28 Side wall (side plate) 32 Flange (end retaining member) 38 Thermistor (temperature detection component) 39 Thermostat (temperature sensing device or power cut-off device) 50 Base material 60 Resistance Heating Element 61 Electrode part (power supply part) 65A central heating section 65B End side heating part 70 Connector (power supply component) A Paper transport direction C split area M Heating area of ​​heater M1 Center position of the heater heating area N Fixing nip (nip part) P Paper (recording medium) X Longitudinal direction Y Short side [Prior art documents] [Patent documents]

[0139] [Patent Document 1] JP 2002-72719 A

Claims

1. An endless belt member; an opposing member opposed to the belt member; A heating element; a nip forming member provided on an inner side of the belt member and forming a nip portion between the belt member and the opposing member; a holding member for holding the nip forming member; A heating device including a support member that supports the holding member from an opposite side to the opposing member, The heating member and the nip forming member may be the same member or different members, If the center position of the heating area in the longitudinal direction of the heating member is defined as the center position in the longitudinal direction, At least one of the nip forming member and the holding member has a plurality of nip forming member positioning portions, and the nip forming member is positioned by contacting the holding member in a direction from the upstream side to the downstream side of the rotation direction of the belt member at the nip forming member positioning portions, the nip forming member positioning portion includes a first nip forming member positioning portion and a second nip forming member positioning portion disposed on one side and the other side of the central position in the longitudinal direction, respectively, and a third nip forming member positioning portion disposed closer to the central position than the first nip forming member positioning portion and the second nip forming member positioning portion, At least one of the holding member and the supporting member has a holding member positioning portion, and the holding member is positioned by contacting the holding member with the supporting member in a direction from the upstream side to the downstream side in a rotation direction of the belt member at the holding member positioning portion, In the longitudinal direction, the holding member positioning portion is disposed closer to the central position than at least one of the first nip forming member positioning portion and the second nip forming member positioning portion, the heating member and the nip forming member are the same member, The heating member is made of one or more resistive heating elements and includes a central heating portion and an end heating portion that can be energized independently of each other; the central heat generating portion is provided at a position closer to a central position in the longitudinal direction than the end heat generating portions, A heating device characterized in that at least one of the nip forming member positioning portion or the holding member positioning portion is provided at a position in the longitudinal direction outer than the central heat generating portion, outer than the area through which the widest recording medium among the recording media that the central heat generating portion corresponds to passes, and corresponding to an area through which a recording medium one width wider than the recording medium passes.

2. A heating device as described in claim 1, wherein at least one of the nip forming member positioning portion or the holding member positioning portion is provided in the longitudinal direction within the area through which a recording medium of the widest width that the heating device can accommodate passes, at a position corresponding to the outside of the area through which a recording medium one width smaller than the recording medium passes.

3. An endless belt member; an opposing member opposed to the belt member; A heating element; a nip forming member provided on an inner side of the belt member and forming a nip portion between the belt member and the opposing member; a holding member for holding the nip forming member; A heating device including a support member that supports the holding member from an opposite side to the opposing member, The heating member and the nip forming member may be the same member or different members, If the center position of the heating area in the longitudinal direction of the heating member is defined as the center position in the longitudinal direction, At least one of the nip forming member and the holding member has a plurality of nip forming member positioning portions, and the nip forming member is positioned by contacting the holding member in a direction from the upstream side to the downstream side of the rotation direction of the belt member at the nip forming member positioning portions, the nip forming member positioning portion includes a first nip forming member positioning portion and a second nip forming member positioning portion disposed on one side and the other side of the central position in the longitudinal direction, respectively, and a third nip forming member positioning portion disposed closer to the central position than the first nip forming member positioning portion and the second nip forming member positioning portion, At least one of the holding member and the supporting member has a holding member positioning portion, and the holding member is positioned by contacting the holding member with the supporting member in a direction from the upstream side to the downstream side in a rotation direction of the belt member at the holding member positioning portion, In the longitudinal direction, the holding member positioning portion is disposed closer to the central position than at least one of the first nip forming member positioning portion and the second nip forming member positioning portion, the heating member and the nip forming member are the same member, The heating member is made of one or more resistive heating elements and includes a central heating portion and an end heating portion that can be energized independently of each other; the central heat generating portion is provided at a position closer to a central position in the longitudinal direction than the end heat generating portions, A heating device characterized in that, in the longitudinal direction, at least one of the nip forming member positioning portion or the holding member positioning portion is provided at a position within the area through which the recording medium of the widest width that the heating device can accommodate passes, which corresponds to the outside of the area through which a recording medium one width narrower than the recording medium passes.

4. The heating device according to claim 1 , further comprising a plurality of the holding member positioning portions, In the longitudinal direction, at least one of the holding member positioning portions is disposed on one side of the central position and is disposed closer to the central position than the first nip forming member positioning portion, At least one of the holding member positioning portions is disposed on the other side of the central position and is disposed closer to the central position than the second nip forming member positioning portion.

5. The heating device according to claim 1 , wherein at least a portion of the third nip forming member positioning portion is disposed in an area through which a recording medium having a minimum length that the heating device can accommodate passes in the longitudinal direction.

6. The heating device according to claim 1 , wherein the third nip forming member positioning portion is disposed at the central position in the longitudinal direction.

7. The heating device according to claim 1 , wherein the holding member positioning portion is disposed at the central position in the longitudinal direction.

8. The heating device according to claim 1 , wherein the third nip forming member positioning portion and the holding member positioning portion are arranged to overlap each other in the longitudinal direction.

9. The heating member includes a plurality of resistance heating elements arranged side by side in the longitudinal direction, 9. The heating device according to claim 1, wherein at least one of the nip forming member positioning portion and the holding member positioning portion is provided at a position corresponding to a dividing region between the resistance heating elements in the longitudinal direction.

10. The heating member includes a plurality of resistance heating elements arranged side by side in the longitudinal direction, 9. The heating device according to claim 1, wherein at least one of the nip forming member positioning portion and the holding member positioning portion is provided at a position outside a region separating the resistance heating elements in the longitudinal direction.

11. the heating member includes a resistance heating element and a plurality of power supply parts that contact a power supply member and supply power to the resistance heating element; The heating device according to claim 1 , wherein the nip forming member positioning portion is provided at a position corresponding to the power supply portion in the longitudinal direction.

12. The heating device according to claim 1 , further comprising a temperature detection member, the nip forming member positioning portion is provided at a position corresponding to the temperature detecting member in the longitudinal direction of the heating device.

13. The heating device according to claim 1 , wherein the holding member is made of a resin material, and the supporting member is made of a material having a higher rigidity than the holding member.

14. The heating device according to claim 1 , wherein the nip forming member positioning portion and the holding member positioning portion position the nip forming member or the holding member from a downstream side of the nip forming member in a rotational direction of the belt member.

15. A heating device described in any one of claims 1 to 14, wherein the longitudinal width of some or all of the first nip forming member positioning portion, the second nip forming member positioning portion, and the third nip forming member positioning portion is larger than the longitudinal width of the holding member positioning portion.

16. A heating device described in any one of claims 1 to 14, wherein the longitudinal widths of some or all of the first nip forming member positioning portion, the second nip forming member positioning portion, and the third nip forming member positioning portion are smaller than the longitudinal width of the holding member positioning portion.

17. The heating device according to claim 1 , wherein the belt member has a base layer made of a resin material.

18. 18. The heating device according to claim 1, wherein the belt member is a rubberless belt that does not have an elastic layer made of rubber.

19. 19. The heating device according to claim 1, which is a fixing device for fixing toner on a recording medium by heat.

20. 19. The heating device according to claim 1, which is a drying device that dries a liquid on a recording medium by heat.

21. 21. An image forming apparatus comprising the heating device according to claim 19 or 20.

Images