Fixing device and image forming apparatus

Abstract

To provide a fixing device that can suppress the occurrence of image defects. [Solution] The fixing device 7 includes a fixing belt 20 for heating toner on paper, a pressure roller for pressurizing toner on paper as it passes through a pressure area, a heater 22 for heating the fixing belt 20, a heat equalization member 23 that contacts one surface of the heater 22 and absorbs the heat emitted from the heater 22 and moves in the axial direction, a support member 26 that contacts one surface of the heat equalization member 23 and supports the heat equalization member 23, and a positioning structure 40 for positioning the heat equalization member 23 with respect to the support member 26. The positioning structure 40 has a positioning hole 41 that penetrates in the thickness direction in the axial intermediate region of the heat equalization member 23, a positioning recess 42 that is recessed in the thickness direction in the axial intermediate region of the support member 26 that coincides with the positioning hole 41, and a positioning member 43 that fits into a positioning space S1 formed by the positioning hole 41 and the positioning recess 42 while in contact with one surface of the heater 22.

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a medium and an image forming apparatus. [Background technology]

[0002] An image heating device (fixing device) is known that heats toner on a recording material while the recording material passes through a fixing nip between an endless belt and a rotating body (Patent Document 1). The image heating device includes a heating member in contact with the inner peripheral surface of the endless belt, a holding member that holds the heating member, and a heat conductive member sandwiched between the heating member and the holding member. The heat conductive member is formed in a rectangular shape and is engaged with the holding member via a restricting portion formed on one side in the longitudinal direction. The restricting portion restricts longitudinal movement of the heat conductive member relative to the holding member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-72780 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the image heating device (fixing device) described above, heat from the heating element is also transferred to the heat conduction element, causing the heat conduction element to thermally expand (stretch) primarily in the other longitudinal direction, the side opposite the regulating portion. This causes the heat conduction element to significantly move (shift) in the other longitudinal direction relative to the heating element, resulting in an uneven temperature distribution in the heating element (belt). As a result, the toner on the recording material cannot be properly heated, which can result in poor image quality.

[0005] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that can suppress the occurrence of image defects. [Means for solving the problem]

[0006] The fixing device of the present invention comprises: a fixing belt formed in a cylindrical shape that heats toner on a medium while rotating around an axis; a pressurizing member that forms a pressurizing region between itself and the fixing belt and pressurizes the toner on the medium as it passes through the pressurizing region while rotating around an axis; a heater that extends in the axial direction of the fixing belt, contacts the inner surface of the fixing belt facing the pressurizing region, and heats the fixing belt; and a component that extends in the axial direction to be less than or equal to the axial dimension of the heater, contacts one surface of the heater opposite to the fixing belt, and absorbs the heat emitted from the heater. The system comprises a heat equalization member that moves in the axial direction, a support member that contacts one surface of the heat equalization member opposite to the heater and supports the heat equalization member, and a positioning structure that positions the heat equalization member with respect to the support member, wherein the positioning structure has a positioning hole that penetrates in the thickness direction in the intermediate region of the heat equalization member in the axial direction, a positioning recess that is recessed in the thickness direction in the intermediate region of the support member in the axial direction that coincides with the positioning hole, and a positioning member that fits into the positioning space formed by the positioning hole and the positioning recess while in contact with the one surface of the heater.

[0007] In this case, the positioning structure further includes a biasing member provided between the support member and the positioning member within the positioning space, wherein the biasing member presses the positioning member against one surface of the heater.

[0008] In this case, the positioning structure may further have a plurality of rotation restricting portions that protrude from the support member toward the heater, and the plurality of rotation restricting portions may contact the side surface of the heat equalization member and restrict the rotation of the heat equalization member around the positioning member.

[0009] In this case, the positioning structure may further include at least one anti-rotation hole penetrating the heat equalizing member in the thickness direction on at least one of both axial regions of the heat equalizing member, at least one anti-rotation recess recessed in the thickness direction on at least one of both axial regions of the support member that coincides with the anti-rotation hole, and at least one anti-rotation member placed in an anti-rotation space formed by the anti-rotation hole and the anti-rotation recess while in contact with the one surface of the heater, and at least one of the anti-rotation hole and the anti-rotation recess may be formed to be longer in the axial direction than the anti-rotation member, thereby allowing relative movement of the anti-rotation member in the axial direction.

[0010] In this case, the thermal conductivity (λ1) of the temperature equalizing member, the thermal conductivity (λ2) of the support member, and the thermal conductivity (λ3) of the positioning member may satisfy the relationship (λ3)≧(λ1)>(λ2).

[0011] An image forming apparatus according to the present invention includes the fixing device described above. [Effects of the Invention]

[0012] According to the present invention, the occurrence of image defects can be suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram (side view) showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 2 is a bottom view showing a heater of a fixing device according to an embodiment of the present invention. [Figure 5] FIG. 2 is a plan view showing a heater, a heat equalizing member, and a positioning structure of a fixing device according to an embodiment of the present invention. [Figure 6] 6 is a cross-sectional view taken along the line VI-VI in FIG. 5. [Figure 7]FIG. 10 is a cross-sectional view showing a heater, a heat equalizing member, and a positioning structure of a fixing device according to a first modified example of one embodiment of the present invention. [Figure 8] FIG. 10 is a plan view showing a heater, a heat equalizing member, and a positioning structure of a fixing device according to a second modified example of one embodiment of the present invention. [Figure 9] 9 is a cross-sectional view taken along line IX-IX in FIG. 8. [Figure 10] FIG. 10 is a plan view showing a heater, a heat equalizing member, and a positioning structure of a fixing device according to a third modified example of one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, Fr, Rr, L, R, U, and D indicate front, rear, left, right, top, and bottom. The front-to-back direction, left-to-right direction (axial direction), and top-to-bottom direction are perpendicular to one another. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention. Furthermore, the terms "upstream," "downstream," and similar terms refer to "upstream" and "downstream" in the transport direction of paper P (medium) and similar concepts. In each drawing, the dimensions and angles of components are not accurate and are shown schematically for the purpose of explanation.

[0015] An image forming apparatus 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (side view) showing the image forming apparatus 1.

[0016] The image forming apparatus 1 is an electrophotographic printer. The image forming apparatus 1 has an apparatus main body 2 that has a substantially rectangular parallelepiped appearance. A paper feed cassette 3 that stores, for example, paper P (medium) is detachably provided at the bottom of the apparatus main body 2. A paper output tray 4 is provided on the top surface of the apparatus main body 2. Note that the paper P, which is an example of a medium, is not limited to being made of paper, and may be a resin sheet or the like.

[0017] The image forming apparatus 1 includes a paper feeder 5, an imaging device 6, and a fixing device 7. The paper feeder 5 is provided at the upstream end of a transport path 9A that extends from the paper feed cassette 3 to the paper output tray 4, and sends out paper P stored in the paper feed cassette 3 one sheet at a time to the transport path 9A. The imaging device 6 is provided in the middle of the transport path 9A, and forms a toner image on the transported paper P. The fixing device 7 is provided downstream of the transport path 9A, and thermally fixes the toner image to the paper P.

[0018] The conveying path 9A is provided with a pair of registration rollers 10A that temporarily block the conveyed paper P to correct (skew correct) the inclination of the paper P. Below the conveying path 9A, a reversing conveying path 9B is provided that branches off on the downstream side of the conveying path 9A and merges with the upstream side of the conveying path 9A. The reversing conveying path 9B is provided with a plurality of pairs of conveying rollers 10B that convey the paper P.

[0019] The image forming device 6 includes a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is located at the upper front of the device main body 2 and contains, for example, black toner (developer). The drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape and is driven to rotate about its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged around the photosensitive drum 14 in the order of the image formation process. The transfer roller 17 contacts the photosensitive drum 14 from below to form a transfer nip. The optical scanning device 13 is located above the photosensitive drum 14 and emits scanning light toward the surface of the photosensitive drum 14.

[0020] The image forming apparatus 1 is provided with a control device 8 that controls the entire apparatus. The control device 8 may be configured with a processor, or may be configured with a logic circuit (hardware) formed in an integrated circuit or the like. When configured with a processor, the processor reads and executes programs stored in memory to perform various processes.

[0021] [Image formation processing] A control device 8 that controls the image forming apparatus 1 performs the following image forming process based on image data input from an external terminal.

[0022] The charging device 15 charges the surface of the photosensitive drum 14, and the optical scanning device 13 emits scanning light based on image data to form an electrostatic latent image on the photosensitive drum 14. The developing device 16 develops a toner image on the photosensitive drum 14 using toner supplied from the toner container 11. The paper feeder 5 feeds paper P one sheet at a time from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew-corrected by a pair of registration rollers 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photosensitive drum 14 to the surface of the paper P as it passes through the transfer nip. The fixing device 7 thermally fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fixing device 7 is discharged to the paper output tray 4.

[0023] In the case of double-sided printing, the paper P that has passed through the fixing device 7 switches back at the downstream end of the conveying path 9A and is sent to the reverse conveying path 9B. The paper P is conveyed by the conveying roller pair 10B, returned from the reverse conveying path 9B to the conveying path 9A again, and after skew correction by the registration roller pair 10A, is sent to the transfer nip. Thereafter, the toner image is transferred onto the paper P and thermally fixed, and the double-sided printed paper P is discharged onto the paper output tray 4.

[0024] [Fixing device] Next, the fixing device 7 will be described with reference to Figures 2 to 6. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a bottom view showing the heater 22. Figure 5 is a plan view showing the heater 22, the heat equalization member 23, and the positioning structure 40.

[0025] As shown in Figures 2 and 3, the fixing device 7 comprises a fixing belt 20, a pressure roller 21, a heater 22, and a heat equalization member 23. The fixing belt 20 and the pressure roller 21 are supported by a frame (not shown), and the frame is fixed to the device body 2.

[0026] <Fixing belt> The fixing belt 20 is an endless belt formed in a generally cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of a heat-resistant and flexible material (polymer resin, metal, or a combination of polymer resin and metal). A pair of holding members 24 (see FIG. 2) is inserted into both left and right ends of the fixing belt 20. The pair of holding members 24 guide the fixing belt 20 to rotate around its axis while maintaining its generally cylindrical shape. The fixing belt 20 is supported by a frame (not shown) via the pair of holding members 24.

[0027] As shown in FIG. 3, a bridge member 25 and a support member 26 are provided in the space surrounded by the fixing belt 20. The bridge member 25 is formed, for example, from a metal material such as stainless steel into a generally rectangular cylindrical shape that is elongated in the left-right direction (axial direction), and is bridged between the pair of holding members 24. The support member 26 is fixed to the lower part of the bridge member 25. The support member 26 is formed, for example, from a heat-resistant and abrasion-resistant synthetic resin into a generally semi-cylindrical shape that is elongated in the left-right direction. The support member 26 curves along the inner surface of the fixing belt 20 and contacts the lower side of the inner surface of the fixing belt 20 (the side of the pressure region N). A fitting portion 26A into which the heater 22 is fitted is recessed in the lower part of the support member 26.

[0028] <Pressure Roller> As shown in Figures 2 and 3, a pressure roller 21, as an example of a pressure member, is formed in a roughly cylindrical shape that is long in the left-right direction. The pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on its outer surface (see Figure 3). A drive motor M is connected to the left end of the core 21A via a gear train (not shown) (see Figure 2). The pressure roller 21 contacts the fixing belt 20 from below, forming a pressure region N between it and the fixing belt 20. As the paper P passes through the pressure region N, a toner image is fixed onto the paper P. The pressure region N refers to the area from the upstream position where the pressure is 0 Pa, through the position where pressure is applied, to the downstream position where the pressure becomes 0 Pa again.

[0029] The paper P is transported with its width centered roughly aligned with the center of the pressurized area N in the left-right direction (axial direction). For this reason, the fixing belt 20 (or pressurized area N) is configured with a passage area A1 in the axial center that contacts the paper P, and non-passage areas A2 on both sides in the axial direction that do not contact the paper P (see Figure 4). The area near the axial center of the passage area A1 always comes into contact with the transported paper P, regardless of its size (dimensions in the left-right direction). In contrast, the areas on both sides in the axial direction of the passage area A1 come into contact with paper P of normal size (e.g., A4 size), but not with paper P of smaller size (e.g., A5, B5 size, etc.).

[0030] <Heater> As shown in Figures 3 and 4, the heater 22 extends in the left-right direction (axial direction) of the fixing belt 20 and is fitted into the fitting portion 26A of the support member 26. The heater 22 contacts the inner surface of the fixing belt 20 facing the pressurized area N and heats the fixing belt 20. As shown in Figure 4, the heater 22 has a substrate 30 and a heating element 31.

[0031] The substrate 30 is made of an insulator (electrical insulating material) such as ceramic and is formed in a roughly rectangular plate shape that is long in the left-right direction (axial direction). The axial dimension of the substrate 30 (heater 22) is set to be less than or equal to the axial dimension of the fixing belt 20. The heating element 31 is provided on the lower surface of the substrate 30, which is on the inner side of the fixing belt 20. The heating element 31 consists of three resistive heating elements 32A to 32C arranged in a row with a gap G in between in the axial direction. In this specification, when describing the three resistive heating elements 32A to 32C in common, only Arabic numerals will be used for the reference numerals. The gap G is set to an insulating distance (creepage distance) that can prevent creepage discharge between adjacent resistive heating elements 32.

[0032] The resistive heating element 32 is formed in a roughly rectangular shape using a metal material with high electrical resistance. The entire heating section 31 is shorter than the total length of the fixing belt 20 in the left-right direction (axial direction), and longer in the axial direction than the passage area A1 of the fixing belt 20. In other words, both sides of the resistive heating elements 32B and 32C, located on the outer sides in the axial direction, face the non-passing area A2 of the fixing belt 20. The resistive heating element 32A, located in the center in the axial direction, corresponds to the left-right width of a small-sized paper P, while all of the resistive heating elements 32A to 32C correspond to the left-right width of a standard-sized paper P.

[0033] Three individual electrodes 33A to 33C and a common electrode 33D are formed on the lower surface of the substrate 30. The three individual electrodes 33A to 33C and the common electrode 33D are formed of a metal material with a lower electrical resistance than the resistive heating element 32, for example. In this specification, when describing the three individual electrodes 33A to 33C and the common electrode 33D in common, they will simply be referred to as "electrode section 33" and will be denoted only by Arabic numerals.

[0034] Individual electrode 33A is connected to the downstream end (rear end) of the resistive heating element 32A, which is located in the axial center. The other individual electrodes 33B and 33C are connected to the downstream ends of the resistive heating elements 32B and 32C, respectively. The common electrode 33D is connected to the upstream end (front end) of all resistive heating elements 32A to 32C. Each of the multiple electrode sections 33 extends from the portion connected to the heating element 31 to both outer sides of the heating element 31 in the axial direction. The multiple electrode sections 33 are electrically connected to equipment such as a power supply (not shown) on both sides of the substrate 30 in the axial direction.

[0035] The heating element 31 and the electrode element 33 are covered with a coating layer (not shown). The heater 22 is fitted into the fitting portion 26A of the support member 26, and the coating layer is in contact with the inner surface of the fixing belt 20. The heater 22 receives the fixing belt 20 pressed against the pressure roller 21, thereby forming a pressurized area N at the contact point between the fixing belt 20 and the pressure roller 21. The fixing device 7 is also provided with a temperature detection unit (not shown) for detecting the temperature of the heater 22. The heater 22, drive motor M, and temperature detection unit are electrically connected to a control device 8 and a power supply (not shown), etc. The control device 8 controls the power supply and the heater 22 as appropriate.

[0036] <Heat-equalizing member> Since the fixing belt 20 has a smaller heat capacity compared to rollers, etc., a fixing device 7 employing a fixing belt 20 has the advantage of a shorter warm-up time. However, for example, when fixing small-sized paper P continuously, excessive heating is suppressed in most of the area A1 through which the fixing belt 20 passes because the paper P (toner image) absorbs heat. However, the axial ends of the area A1 through which the paper P does not pass and the non-passing area A2 may become excessively hot. Therefore, in the fixing device 7 according to this embodiment, a heat equalization member 23 is provided on the heater 22 to suppress excessive heating in the non-passing area A2 and other areas of the fixing belt 20.

[0037] The heat equalization member 23 is formed in a substantially rectangular plate shape from a metal material such as an aluminum alloy. As shown in Figure 5, the heat equalization member 23 extends axially so as to be less than or equal to the left-right (axial) dimension of the heater 22. As shown in Figures 5 and 6, the heat equalization member 23 is provided (in contact with) the upper surface (one side) of the heater 22 (substrate 30) on the side opposite to the fixing belt 20 (pressure region N). The support member 26 described above is in contact with the upper surface (one side) of the heat equalization member 23 on the side opposite to the heater 22 and supports the heat equalization member 23 (see Figure 3).

[0038] The heat equalization member 23 is in contact with the substrate 30 of the heater 22, with a lubricant such as silicone grease (not shown) in between. The lubricant ensures that the heat equalization member 23 adheres closely to the substrate 30 and facilitates the transfer of heat from the heater 22 to the heat equalization member 23. The heat equalization member 23 is positioned to cover the three resistance heating elements 32A to 32C, absorbing the heat emitted from the heater 22 and transferring it axially. In other words, the heat equalization member 23 equalizes the temperature of the heater 22 along the axial direction. As a result, the temperature of the fixing belt 20 is also equalized along the axial direction, and excessive heating in the non-passing region A2 is suppressed. In this specification, the term "uniform" does not refer only to a perfectly constant state, but rather to allowing for some error.

[0039] [Fixing process] Here, the operation of the fixing device 7 (fixing process) will be explained. The control device 8 drives and controls the drive motor M, causing the pressure roller 21 to rotate around its axis. The fixing belt 20 rotates in accordance with the pressure roller 21 (see arrow in Figure 3). The control device 8 also receives a detection signal from the temperature detection unit and controls the heater 22 (or power supply) to maintain a preset target temperature. The heater 22 (heating unit 31) generates heat when energized, heating the fixing belt 20 (pressure region N).

[0040] In this process, the control device 8 changes which of the three resistance heating elements 32A to 32C are heated (energized) according to the size of the paper P. For example, when a standard-sized paper P passes through the pressurized area N, the control device 8 controls all of the resistance heating elements 32A to 32C to heat up. When a small-sized paper P passes through the pressurized area N, the control device 8 controls only one of the resistance heating elements 32A to heat up. This allows only the necessary portion of the fixing belt 20 (pressurized area N) to be heated according to the size of the paper P. As a result, the power used can be kept to the absolute minimum. Furthermore, overheating of both ends of the fixing belt 20 in the axial direction can be suppressed.

[0041] When the fixing belt 20 (heater 22) reaches the target temperature, the control device 8 starts the image formation process described above. The paper P on which the toner image has been transferred enters the pressurized area N. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressurized area N while rotating around its axis. The pressurized roller 21 pressurizes the toner on the paper P as it passes through the pressurized area N while rotating around its axis. As a result, the toner image is fixed to the paper P, and a fixed image is formed on the paper P. The paper P with the fixed image is then discharged into the output tray 4.

[0042] [Positioning structure] Incidentally, the heat equalization member 23 receives heat from the heater 22 and therefore expands mainly in the axial direction (longitudinal direction). The support member 26 also receives heat and expands, but the support member 26, made of synthetic resin, is less conductive to heat than the metal heat equalization member 23 and therefore expands less. Considering the difference in thermal expansion coefficients between the support member 26 and the heat equalization member 23, the support member 26 needs to support the heat equalization member 23 in a way that allows for the heat equalization member 23's expansion. Therefore, the fixing device 7 is equipped with a positioning structure 40 that positions the heat equalization member 23 relative to the support member 26 while allowing for the heat equalization member 23's expansion. By being positioned on the support member 26, the heat equalization member 23 is also positioned relative to the heater 22. Note that "positioning" does not mean requiring fixing, but rather placing within a desired range.

[0043] The positioning structure 40 will be described with reference to Figures 5 and 6. Figure 6 is a cross-sectional view taken along line VI-VI in Figure 5.

[0044] As shown in Figures 5 and 6, the positioning structure 40 has a positioning hole 41 formed in the heat-equalizing member 23, a positioning recess 42 formed in the support member 26, a positioning member 43 that determines the position of the heat-equalizing member 23 in the axial direction (longitudinal direction), and a plurality of rotation control members 44 that determine the position of the heat-equalizing member 23 in the transport direction (transverse direction).

[0045] <Positioning holes> The positioning hole 41 penetrates the temperature equalizing member 23 in the thickness direction in an axially intermediate region thereof. Specifically, the positioning hole 41 is a circular hole with a circular opening when the temperature equalizing member 23 is viewed from the top (or bottom). The positioning hole 41 is formed in the center of the temperature equalizing member 23 in the axial direction (longitudinal direction) and in the transport direction (lateral direction). In other words, the positioning hole 41 is formed at the centroid of the temperature equalizing member 23 when viewed from the top (or bottom).

[0046] <Positioning recess> The positioning recess 42 is recessed in the thickness direction in the axial middle region of the support member 26, coinciding with the positioning hole 41. Specifically, the positioning recess 42 is a circular hole with a circular top surface when the support member 26 is viewed from the bottom. The inner diameter of the positioning recess 42 is approximately the same as the inner diameter of the positioning hole 41. The positioning recess 42 is formed in the center of the support member 26 in the axial direction (longitudinal direction) and in the conveying direction (lateral direction). The positioning recess 42 is recessed from the bottom surface of the support member 26 to near the center of the thickness.

[0047] The temperature equalizing member 23 is sandwiched between the heater 22 (upper surface of the substrate 30) and the support member 26 (top surface of the fitting portion 26A). The temperature equalizing member 23 and the support member 26 are stacked with the positioning holes 41 and positioning recesses 42 aligned. The positioning holes 41 and positioning recesses 42 form a positioning space S1 that houses the positioning member 43. More specifically, the positioning space S1 is a substantially cylindrical space surrounded by the upper surface of the heater 22 (substrate 30), the inner circumferential surfaces of the positioning holes 41, the inner circumferential surfaces of the positioning recesses 42, and the top surface.

[0048] <Positioning component> The positioning member 43 is formed in a substantially cylindrical shape from a metal material such as an aluminum alloy. The outer diameter of the positioning member 43 is set to be slightly smaller than the inner diameter of the positioning holes 41, etc. The height of the positioning member 43 is set to be slightly smaller than the sum of the thickness of the soaking member 23 (the height of the positioning holes 41) and the height (depth) of the positioning recesses 42.

[0049] The positioning member 43 is fitted into the positioning space S1 while contacting the upper surface (one surface) of the heater 22 (substrate 30). The lower surface of the positioning member 43 is in close contact with the upper surface of the heater 22, and the upper surface of the positioning member 43 faces the ceiling surface of the positioning recess 42 with a small gap between them. Furthermore, the outer peripheral surface of the positioning member 43 faces the inner peripheral surfaces of the positioning hole 41 and the positioning recess 42 with an extremely small gap between them. In other words, the positioning member 43 is fitted into the positioning space S1 without any rattle in the radial direction (front-rear and left-right directions).

[0050] <Rotation Control Section> The rotation restricting portions 44 (for example, two) are integrally molded with the support member 26 and protrude from the support member 26 toward the heater 22. Specifically, the two rotation restricting portions 44 are provided on the upstream side (front) of the support member 26 in the transport direction and on both sides in the axial direction (left and right direction) (see FIG. 5). Each rotation restricting portion 44 is formed in a substantially rectangular parallelepiped shape and protrudes downward from the top surface of the fitting portion 26A (see FIG. 6). The lower end surface of each rotation restricting portion 44 does not contact the heater 22, but faces the upper surface of the heater 22 (substrate 30) with a small gap therebetween. The two rotation restricting portions 44 contact the side surface of the temperature equalizing member 23 on the upstream side in the transport direction and restrict rotation of the temperature equalizing member 23 around the positioning member 43.

[0051] The positioning member 43 fits into the positioning space S1, and the two rotation restricting parts 44 contact the heat equalization member 23, thereby positioning the heat equalization member 23 relative to the support member 26. Furthermore, by being positioned relative to the support member 26, the heat equalization member 23 is also positioned relative to the heater 22.

[0052] As described above, the support member 26 is made of synthetic resin, and the temperature equalizing member 23 and the positioning member 43 are made of metal. Because the positioning member 43 is housed in the positioning space S1 and also functions as part of the temperature equalizing member 23, in this embodiment, the positioning member 43 is made of the same material as the temperature equalizing member 23. In this embodiment, the thermal conductivity (λ1) of the temperature equalizing member 23, the thermal conductivity (λ2) of the support member 26, and the thermal conductivity (λ3) of the positioning member 43 satisfy the relationship (λ3) = (λ1) > (λ2). The thermal conductivity (λ3) of the positioning member 43 may be greater than the thermal conductivity (λ1) of the temperature equalizing member 23. In other words, the thermal conductivities of the temperature equalizing member 23, the support member 26, and the positioning member 43 may satisfy the relationship (λ3) ≥ (λ1) > (λ2). While the positioning member 43 is made of a metal material, it is not limited to this and may be made of anisotropic thermally conductive graphite or the like.

[0053] [Function of the positioning structure] The function of the positioning structure 40 will now be described. When the fixing device 7 performs a fixing process, the temperature equalizing member 23 and the support member 26 receive heat from the heater 22 and thermally expand. Because the temperature equalizing member 23 transfers heat more easily than the support member 26, the temperature equalizing member 23 thermally expands primarily along the axial direction (increasing in axial dimension). The positioning member 43 is provided at the center of the temperature equalizing member 23, etc., and the temperature equalizing member 23 is positioned relative to the support member 26 via the positioning member 43. Therefore, the temperature equalizing member 23 thermally expands approximately evenly toward both outer sides in the axial direction (left and right directions) around the positioning member 43 (see the dashed arrows in FIG. 5). In other words, even in a thermally expanded state, the temperature equalizing member 23 has a shape that is line-symmetrical about the positioning member 43.

[0054] According to the fixing device 7 of this embodiment described above, the heat equalizing member 23 can transfer the heat generated by the heater 22 substantially uniformly throughout the entire axial direction, thereby suppressing uneven temperature distribution in the fixing belt 20. This allows the toner on the medium to be heated appropriately, thereby suppressing the occurrence of image defects. Furthermore, since the positioning member 43 fitted into the positioning space S1 is in contact with the heater 22, it can appropriately absorb the heat generated by the heater 22. This prevents excessive temperature changes (temperature increases or decreases) in the portion of the heater 22 corresponding to the positioning space S1.

[0055] Furthermore, according to the fixing device 7 of this embodiment, the rotation regulating portion 44 of the support member 26 is in contact with the side surface of the heat equalizing member 23 in the conveying direction (short direction), so that it is possible to regulate the rotation of the heat equalizing member 23 around the positioning member 43 while allowing thermal expansion of the heat equalizing member 23 on both sides in the axial direction.

[0056] Furthermore, in the fixing device 7 according to this embodiment, the thermal conductivity (λ1) of the heat uniforming member 23 is set to be greater than the thermal conductivity (λ2) of the support member 26, and the thermal conductivity (λ3) of the positioning member 43 is set to be greater than or equal to the thermal conductivity (λ1) of the heat uniforming member 23 ((λ3)≧(λ1)>(λ2)). As a result, the positioning member 43 fitted into the positioning space S1 functions as part of the heat uniforming member 23, making it possible to make the temperature of the fixing belt 20 generally uniform along the axial direction.

[0057] In the positioning structure 40 of the fixing device 7 according to this embodiment, two rotation restricting parts 44 were provided spaced apart in the left-right direction on the upstream side of the support member 26 in the transport direction, but the present invention is not limited to this. For example, two rotation restricting parts 44 may be provided spaced apart in the left-right direction on the downstream side of the support member 26 in the transport direction. Alternatively, for example, two rotation restricting parts 44 may be provided spaced apart in the transport direction (front-back direction) on one side of the axial direction of the support member 26 and in contact with both sides of the heat soaking member 23 in the transport direction (not shown). Furthermore, the rotation restricting parts 44 are not limited to two, but three or more may be provided (not shown).

[0058] [Variations] Hereinafter, modified examples of the fixing device 7 according to this embodiment will be described with reference to Figures 7 to 10. Figure 7 is a cross-sectional view showing the heater 22, heat equalization member 23, and positioning structure 40 of the fixing device 7 according to the first modified example. Figure 8 is a plan view showing the heater 22, heat equalization member 23, and positioning structure 40 of the fixing device 7 according to the second modified example. Figure 9 is a cross-sectional view taken along line IX-IX in Figure 8. Figure 10 is a plan view showing the heater 22, heat equalization member 23, and positioning structure 40 of the fixing device 7 according to the third modified example. The components of the fixing device 7 according to this embodiment described above are denoted by the same reference numerals, and their descriptions are omitted.

[0059] <First Modification> In the fixing device 7 according to the present embodiment described above, the positioning member 43 is held in contact with the upper surface of the heater 22 by its own weight, but the present invention is not limited to this. As shown in FIG. 7 , in the fixing device 7 according to the first modification, the positioning member 45 is held in contact with the upper surface of the heater 22 by a biasing member 46. The biasing member 46 is, for example, a compression coil spring, and is installed between the support member 26 and the positioning member 45 within the positioning space S1. A fitting recess 45A into which the lower part of the biasing member 46 is fitted is formed in the upper part of the positioning member 45. The biasing member 46 biases the positioning member 45 downward, pressing it against the upper surface (one surface) of the heater 22.

[0060] According to the fixing device 7 of the first modified example of the present embodiment described above, the biasing member 46 presses the positioning member 45 against the heater 22, so that the positioning member 45 can be kept in contact with the heater 22. This allows the positioning member 45 to appropriately absorb the heat of the heater 22, so that excessive temperature changes (temperature increases or decreases) in a portion of the heater 22 corresponding to the positioning space S1 can be suppressed.

[0061] The positioning member 43 described above is formed in a cylindrical shape that is thicker (higher) than the temperature equalizing member 23 (see FIG. 6), and therefore the heat capacity of the positioning member 43 is slightly greater than the heat capacity of the temperature equalizing member 23 having the same volume as the positioning hole 41. In contrast, in the fixing device 7 according to the first modified example, a fitting recess 45A (see FIG. 7) is formed on the upper part of the positioning member 45, so that the heat capacity of the positioning member 45 is made substantially the same as the heat capacity of the temperature equalizing member 23 having the same volume as the positioning hole 41. This suppresses excessive temperature changes (temperature rise or temperature drop) near the positioning member 45, and can suppress temperature unevenness in the temperature equalizing member 23, including the positioning member 45.

[0062] <Second Modification> In the fixing device 7 according to the present embodiment, the two rotation restriction members 44 contact the side surfaces of the temperature equalizing member 23 as a structure for restricting the rotation of the temperature equalizing member 23. However, the present invention is not limited to this. As shown in FIGS. 8 and 9 , in a fixing device 7 according to a second modification, the structure for restricting the rotation of the temperature equalizing member 23 is substantially the same as the structure for determining the axial (longitudinal) position of the temperature equalizing member 23 (the positioning hole 41, the positioning recess 42, and the positioning member 43 (45)). Specifically, the positioning structure 40 further includes a rotation stop hole 51 penetrating the temperature equalizing member 23 in the thickness direction in one axial region (the left side in FIG. 8 ) of the temperature equalizing member 23; a rotation stop recess 52 recessed in the thickness direction in one axial region of the support member 26 that coincides with the rotation stop hole 51; and a rotation stop member 53 that contacts the top surface of the heater 22 and is positioned in the rotation stop space S2 formed by the rotation stop hole 51 and the rotation stop recess 52. The rotation stop member 53 has substantially the same structure as the positioning member 43. The rotation prevention hole 51 is an elongated hole formed to be longer in the axial direction (left-right direction) than the rotation prevention member 53, and allows relative axial movement of the rotation prevention member 53. The rotation prevention recess 52 is a round hole (with a bottom) into which the rotation prevention member 53 is fitted to restrict movement.

[0063] The rotation-stopping member 53 is positioned in the rotation-stopping space S2, restricting the rotation of the heat-soothing member 23 around the positioning member 43. Furthermore, when the heat-soothing member 23 expands axially, the rotation-stopping member 53, fitted into the rotation-stopping recess 52, moves relatively axially within the range of the rotation-stopping hole 51. In this way, the rotation of the heat-soothing member 23 can be restricted while allowing thermal expansion on both sides in the axial direction. Note that at least one rotation-stopping hole 51 is required to be formed on at least one side of the axial region of the heat-soothing member 23; for example, a pair of rotation-stopping holes 51 may be formed on both sides of the heat-soothing member 23 in the axial direction (not shown). Similarly, at least one rotation-stopping recess 52 is required to be formed on the support member 26 at a position corresponding to the rotation-stopping hole 51, and at least one rotation-stopping member 53 is required depending on the number of rotation-stopping spaces S2 formed. Furthermore, for example, the rotation-stopping hole 51 may be a round hole that restricts the movement of the rotation-stopping member 53, and the rotation-stopping recess 52 may be an elongated hole that allows relative axial movement of the rotation-stopping member 53 (not shown). Alternatively, both the rotation-stopping hole 51 and the rotation-stopping recess 52 may be elongated holes that allow relative axial movement of the rotation-stopping member 53 (not shown).

[0064] Furthermore, similar to the fixing device 7 (positioning structure 40) according to the first modified example, the biasing member 46 may be installed between the support member 26 and the rotation-stopping member 53 in the rotation-stopping space S2 and pressed against the upper surface (one surface) of the heater 22 (not shown). Also, a recess may be formed in the upper part of the rotation-stopping member 53 for fitting the lower part of the biasing member 46 (not shown).

[0065] In the fixing device 7 according to the present embodiment (including the first and second modifications, the same applies below), the positioning holes 41 and the like are formed in the center (figure center) of the temperature equalizing member 23 and the like, and the positioning member 43 is disposed in the center of the temperature equalizing member 23 and the like. However, the present invention is not limited to this. For example, as shown in FIG. 10 , the positioning holes 41 may be cut in a substantially U-shape from one end of the temperature equalizing member 23 in the transport direction (the front end in FIG. 10 ) toward the center (third modification). In this case, the positioning recesses 42 are formed in the support member 26 so as to coincide with the positioning holes 41. Although not shown, the positioning holes 41 and the like may be formed in a position offset from the center of the temperature equalizing member 23 in the transport direction or in a position offset from the center in the axial direction of the temperature equalizing member 23. In this way, the positioning holes 41 and the like are not necessarily required to be formed in the center (figure center) of the temperature equalizing member 23 and the like, and may be formed in a position offset from the center in the axial direction or the transport direction. In other words, the "central region" referred to in the claims means a region having a certain extent of size that includes the center, and it is sufficient if it satisfies the condition that the heat equalizing member 23 undergoes approximately equal thermal expansion on both sides of the axial direction.

[0066] Furthermore, in the fixing device 7 according to this embodiment, the heat generating section 31 is divided into three resistance heating elements 32A to 32C, but this is not limiting and the heat generating section 31 may be divided into two, four or more, or may not be divided at all (all of which are not shown). Additionally, the heat generating section 31 may be a single resistance heating element extending from one side to the other in the axial direction, or a U-shaped resistance heating element extending from one side to the other in the axial direction and then folding back to extend from the other side to one side in the axial direction (all of which are not shown).

[0067] Furthermore, in the fixing device 7 according to this embodiment, the paper P passes through the center of the pressure region N in the axial direction, but this is not limiting, and the paper P may pass through a position closer to one side in the axial direction of the pressure region N (not shown). In this case, the non-passing region A2 is set only on one side in the axial direction of the fixing belt 20 (or the pressure region N).

[0068] Furthermore, in the fixing device 7 according to this embodiment, the pressure roller 21 is driven to rotate, and the fixing belt 20 is driven to rotate, but this is not limited to this, and the fixing belt 20 may be driven to rotate, and the pressure roller 21 may be driven to rotate.

[0069] Furthermore, in the description of the above embodiment, the present invention has been applied to a monochrome image forming device 1 as an example, but this is not limiting and the present invention may also be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

[0070] The above-described embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0071] 1. Image forming device 7 Fixing device 20 Fixing belt 21 Pressure roller (pressure member) 22 Heater 23 Heat-equalizing member 26 Support member 40 Positioning structure 41 Positioning hole 42 Positioning recess 43,45 Positioning member 44 Rotation restriction part 46 biasing member 51 Rotation stop hole 52 Rotation stop recess 53 Rotation stopper S1 Positioning space S2 Rotation stop space N pressure area P Paper (media)

Claims

1. a fixing belt formed in a cylindrical shape and rotating around its axis to heat the toner on the medium; a pressure member that forms a pressure region between itself and the fixing belt and that pressurizes the toner on the medium that passes through the pressure region while rotating around its axis; a heater extending in the axial direction of the fixing belt, contacting the inner surface of the fixing belt facing the pressure region, and heating the fixing belt; a heat equalizing member that extends in the axial direction so as to be equal to or smaller than the dimension of the heater in the axial direction, that contacts one surface of the heater opposite to the fixing belt, that absorbs heat generated by the heater, and that transfers the heat in the axial direction; a support member that contacts a surface of the temperature equalizing member opposite to the heater and supports the temperature equalizing member; a positioning structure for positioning the temperature equalizing member relative to the support member, The positioning structure includes: a positioning hole penetrating the heat equalizing member in a thickness direction in an intermediate region in the axial direction; a positioning recess recessed in a thickness direction in an axially intermediate region of the support member, the positioning recess coinciding with the positioning hole; a positioning member that is fitted into a positioning space formed by the positioning hole and the positioning recess while being in contact with the one surface of the heater.

2. the positioning structure further includes a biasing member provided between the support member and the positioning member in the positioning space, 2. The fixing device according to claim 1, wherein the biasing member presses the positioning member against the one surface of the heater.

3. the positioning structure further includes a plurality of rotation restriction portions protruding from the support member toward the heater, 3. The fixing device according to claim 1, wherein the plurality of rotation regulating portions contact a side surface of the heat equalizing member and regulate the rotation of the heat equalizing member around the positioning member.

4. The positioning structure includes: at least one rotation stop hole penetrating the temperature equalizing member in a thickness direction in at least one of both side regions in the axial direction; at least one rotation stop recess recessed in a thickness direction in at least one of both axial side regions of the support member, the rotation stop hole being aligned with the rotation stop recess; at least one rotation stop member disposed in a rotation stop space formed by the rotation stop hole and the rotation stop recess in a state of contacting the one surface of the heater, 3. The fixing device according to claim 1, wherein at least one of the rotation stop hole and the rotation stop recess is formed longer in the axial direction than the rotation stop member, thereby allowing relative movement of the rotation stop member in the axial direction.

5. 3. The fixing device according to claim 1, wherein the thermal conductivity (λ1) of the temperature equalizing member, the thermal conductivity (λ2) of the support member, and the thermal conductivity (λ3) of the positioning member satisfy the relationship (λ3) ≧ (λ1) > (λ2).

6. 3. An image forming apparatus comprising the fixing device according to claim 1.

Images