Fixing device and image forming apparatus

Abstract

To provide a fixing device that can accurately maintain the position of a sheet guide part, and an image forming apparatus.SOLUTION: A fixing device 32 has a heating roller 32a as a heating member that heats a sheet, and a pressure roller 32b being a pressure member that is in contact with an outer peripheral surface of the heating roller 32a to form a nip part and applies pressure to a sheet passing through the nip part. An upper cover member 132 being a cover member covering the heating roller 32a and the pressure roller 32b has a sheet guide part 136 guiding a sheet on a re-feeding passage 36. An opposite part 131a of a lower cover member 131 opposite to the sheet guide part 136 of the upper cover member 132 is provided with a regulation projection 135 regulating deformation of the sheet guide part 136.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Conventionally, a fixing device has been known that includes a heating element that heats a sheet, a pressure element that pressurizes the sheet passing through a nip portion formed by contacting the outer peripheral surface of the heating element, and a cover element that covers the heating element and the pressure element.

[0003] Patent Document 1 describes a fixing device having a sheet guide portion that guides a sheet to a cover member. Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a risk that the sheet guide portion may be deformed by the heat of the heating member, making it impossible to maintain the sheet guide position of the sheet guide portion with high precision. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides a fixing device comprising a heating element for heating a sheet, a pressure element for pressurizing the sheet passing through a nip portion formed by contacting the outer peripheral surface of the heating element, and a cover element for covering the heating element and the pressure element, wherein the cover element has a sheet guide portion for guiding the sheet, and a regulating protrusion is provided on an opposing portion facing the sheet guide portion for regulating deformation of the sheet guide portion. [Effects of the Invention]

[0006] According to the present invention, the position of the sheet guide portion can be maintained with high precision. [Brief explanation of the drawings]

[0007] [Figure 1]1 is a diagram showing an outline of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view schematically showing a fixing device. [Figure 3] FIG. 2 is a perspective view schematically showing a fixing device. [Figure 4] 10A and 10B are diagrams showing a restricting protrusion of the lower cover member. [Figure 5] 10A and 10B are diagrams showing other examples of the arrangement of the restriction protrusions. [Figure 6] 5A to 5C are diagrams showing examples of the shape of a restriction protrusion. DETAILED DESCRIPTION OF THE INVENTION

[0008] An image forming apparatus that forms an image by an electrophotographic method will be described below as an embodiment of an image forming apparatus to which the present invention is applied. FIG. 1 is a diagram showing an outline of an image forming apparatus according to one embodiment of the present invention. An image reading device 50 is attached to the top of a device main body 40 which is an image forming device.

[0009] A process cartridge 1 is provided inside the apparatus main body 40. The process cartridge 1 includes a photosensitive member 2 serving as a latent image carrier, and a charging device 3, a developing device 4, and a cleaning device 5, which are arranged around the photosensitive member 2 and serve as process means acting on the photosensitive member 2. The process cartridge 1 is detachably mounted in the apparatus main body 40. The photosensitive member 2, charging device 3, developing device 4, and cleaning device 5 are unitized as the process cartridge 1, making replacement and maintenance easier. Furthermore, the positional accuracy between each component can be maintained at a high level, improving the quality of the images formed.

[0010] The transfer device, which serves as a transfer means, includes a transfer roller 20, which is pressed against and in contact with the circumferential surface of the photosensitive member 2. A fixing device 32, which serves as a fixing means, is provided above the transfer device. The fixing device 32 includes a heating roller 32a, which serves as a heating member, and a pressure roller 32b, which serves as a pressure member. The device main body 100 also includes a laser writing device 30, which serves as a latent image forming means. The laser writing device 30 includes a laser light source, a rotating polygon mirror for scanning, a polygon motor, an fθ lens, and the like. The device main body also includes multiple sheet cassettes 11 for storing sheets P, such as transfer paper and overhead projector films.

[0011] When making copies using an apparatus configured as described above, the user presses the start switch. First, the contents of the document set in the image reading device 50 are read. At the same time, the photoreceptor drive motor rotates the photoreceptor 2, and the charging device 3 uniformly charges the surface of the photoreceptor 2. Next, a writing process is performed using the laser writing device 30, irradiating the photoreceptor with a laser beam according to the contents of the document read by the image reading device 50. Then, an electrostatic latent image is formed on the surface of the photoreceptor 2, and the developing device 4 applies toner to make the electrostatic latent image visible (developed).

[0012] At the same time as the user presses the start switch, a selected sheet P from a multi-stage sheet cassette 11 is sent out by a call roller 11a. Next, the sheets are separated one by one in a separation unit 12 and sent to a supply path 13. The sheet P sent to the supply path 13 is stopped by a registration roller 17. Then, in synchronization with the rotation timing of the visualized toner image on the photosensitive member 2, the sheet P is sent into a transfer nip formed by the transfer roller 20 abutting against the photosensitive member 2.

[0013] The toner image on the photoreceptor 10 is transferred onto the sheet P sent into the transfer nip by the transfer roller 20. After the image transfer, the residual toner on the photoreceptor 2 is removed and cleaned by the cleaning device 5, and the residual potential on the photoreceptor 2 from which the residual toner has been removed is removed by the charge removal device. Then, the photoreceptor 2 is prepared for the next image formation, which begins with the charging device 3. The residual toner removed by the cleaning device 5 is transported to a waste toner bottle.

[0014] Meanwhile, the sheet P after the image transfer is guided to the fixing device 32, passed between a heating roller 32a and a pressure roller 32b, and while being transported between these rollers, heat and pressure are applied to fix the toner image. During single-sided image formation, in which an image is formed on only one side of the sheet P, the sheet P with the fixed image is guided by the branch claw 14 to the paper discharge rollers 33. The paper discharge rollers 33 then discharge the sheet P onto the discharge stack section 34 and stack it thereon.

[0015] During double-sided image formation, the sheet P on which the image has been fixed is guided by the branch claw 14 to the reversing rollers 15, which then transport the sheet P to a reversing tray 35 arranged above the discharged paper stack section 34. Before the trailing end of the sheet P in the transport direction passes through the reversing rollers 15, the reversing rollers 15 are rotated in the reverse direction, and the sheet P is switched back and transported to a resupply path 36, which serves as a reversing transport path. The sheet P transported to the resupply path 36 is transported to registration rollers 17 by a plurality of transport rollers arranged in the resupply path 36. Then, in the same manner as described above, the sheet is sent to the transfer nip, where a toner image is transferred to the back side, which is the second side of the sheet, and the sheet is then discharged onto the discharged paper stack section 34 via the fixing device 32.

[0016] Fig. 2 is a cross-sectional view that schematically shows fixing device 32, and Fig. 3 is a perspective view that schematically shows fixing device 32. In the following explanation, the vertical direction of the sheet passing through the fixing nip is defined as the X direction, the width direction of the sheet passing through the fixing nip (the axial direction of the heating roller) is defined as the Y direction, and the conveyance direction of the sheet passing through the fixing nip (the vertical direction of the device) is defined as the Z direction. The fixing device 32 has a lower cover member 131 and an upper cover member 132, which are resin molded parts that cover the heating roller 32a and the pressure roller 32b. The lower cover member 131 has an inlet section 32c into which the sheet P is conveyed after passing through the transfer nip, and the upper cover member 132 has an outlet section 32d into which the sheet P with the toner image fixed thereon is discharged. Pressure levers 137 for pressing the pressure roller 32b against the heating roller 32a extend from both ends of the outlet section 32d in the Y direction.

[0017] The upper cover member 132 has a sheet guide portion 136 that guides the sheet moving in the resupply path 36. By providing the upper cover member 132 of the fixing device 32 with the sheet guide portion 136 that guides the sheet in the resupply path 36, the resupply path 36 can be disposed close to the fixing device 32, thereby enabling the image forming device to be made more compact.

[0018] The lower cover member 131 is attached to the fixing frame 133, which is a main body frame made of sheet metal, from the -Z direction. The upper cover member 132 is attached to the fixing frame 133 to which the lower cover member 131 is attached from the +Z direction. The upper surface of the upper cover member 132, which is perpendicular to the Z direction, is fastened to the fixing frame 133 with screws 134.

[0019] In this way, the upper surface portion of the upper cover member 132 perpendicular to the Z direction is fastened to the fixing frame 133 with the screws 134, so that the sheet guide portion 136 can be positioned with high precision in the Z direction.

[0020] As shown in FIG. 3, the sheet guide portion 136 has a plurality of guide ribs 136a arranged in the axial direction. When the heights of the guide ribs 136a are h1, h2, h3, and h4, the relationship h4>h3>h2>h1 holds, with the height of the guide ribs increasing toward the axial center. In this embodiment, the height of the guide ribs is varied in four stages, but the height of the guide ribs may be varied in five or more stages. The number of guide ribs 136a and the spacing between the guide ribs 136a may be determined appropriately depending on the device configuration.

[0021] The upper cover member 132 is a molded resin product, and warping can occur after molding, causing a dent in the center portion in the Y direction (axial direction, sheet width direction). If the heights of the guide ribs are the same, the positions in the X direction (vertical direction to the sheet surface) of the tops of the guide ribs 136a that contact and guide the sheet will be misaligned between the center and the end portions in the Y direction. Specifically, the X direction position of the top of the guide rib at the center in the Y direction is located further in the -X direction than the tops of the guide ribs at the end portions in the Y direction. In this case, there is a risk that the sheet in the resupply path 36 will be conveyed with its center portion in the width direction bent in accordance with the warping of the sheet guide portion 136. If the sheet is conveyed in this bent state, it may get caught midway through the resupply path 36, causing a paper jam.

[0022] In contrast, in this embodiment, as described above, the height of the guide ribs 136a increases toward the center in the Y direction. This reduces the misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the tops of the guide ribs at the ends in the Y direction when the center in the Y direction is recessed due to warping after molding. This maintains the positional accuracy of the tops of the guide ribs in the X direction, suppresses bending of sheets in the resupply path 36, and reduces the occurrence of paper jams. Note that in this embodiment, if the misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the tops of the guide ribs at the ends exceeds 1 mm, paper jams may occur. Therefore, the heights h1, h2, h3, and h4 of the guide ribs are set so that the misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the ends in the Y direction due to warping of the sheet guide unit 136 does not exceed 1 mm.

[0023] The fixing frame 133 shown in FIG. 2 is made of sheet metal and is susceptible to temperature rise due to the heat of the heating roller 32a. If the sheet guide portion 136 is in close contact with the fixing frame 133, the fixing frame 133 will cause the temperature of the sheet guide portion 136 to rise. As a result, the toner image on the sheet may be heated by the sheet guide portion 136, remelting it and distorting the image on the sheet. For this reason, in this embodiment, the upper cover member 132 is attached to the fixing frame 133 with a gap d between the sheet guide portion 136 and the fixing frame 133. By providing this gap d, it is possible to suppress temperature rise in the sheet guide portion 136 and prevent the image on the sheet from being distorted. Furthermore, by providing the gap d between the fixing frame 133 and the sheet guide portion 136, the upper cover member 132 can be easily assembled to the fixing frame 133.

[0024] However, the gap d between the sheet guide portion 136 and the fixing frame 133 may cause the following problem. Specifically, the heat of the heating roller 32a during operation of the device may worsen the warping of the sheet guide portion 136, causing the central portion of the sheet guide portion 136 in the Y direction (axial direction) to become further recessed. This makes it difficult to maintain the positional accuracy of the tops of the guide ribs that guide the sheet in the X direction, increasing the misalignment in the X direction between the tops of the guide ribs in the Y direction central portion and the tops of the guide ribs at the Y direction ends. As a result, the sheet in the resupply path 36 is transported with its Y direction central portion warped in accordance with the sheet guide portion 136, and the sheet may get caught midway through the resupply path 36, causing a paper jam.

[0025] Therefore, in this embodiment, a restricting protrusion 135 for restricting deformation of the sheet guide portion 136 is provided on the opposing portion 131a of the lower cover member 131 that faces the sheet guide portion 136.

[0026] FIG. 4 is a view showing the restricting protrusion 135 provided on the facing portion 131a of the lower cover member 131. As shown in FIG. As shown in Figure 4, the regulating protrusion 135 has a predetermined length in the Z direction (sheet conveying direction) and is composed of two convex portions 135a with flat tops, and four of them are arranged at equal intervals of L1 in the Y direction (axial direction and sheet width direction). These restricting protrusions 135 restrict deformation of the sheet guide portion 136 toward the fixing frame, preventing further warping of the sheet guide portion 136. This maintains the positional accuracy of the tops of the guide ribs 136a in the X direction and reduces misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the tops of the guide ribs at the ends. As a result, bending of the sheet in the resupply path 36 can be reduced, preventing paper jams. As described above, in this embodiment, if the misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the tops of the guide ribs at the ends exceeds 1 mm, paper jams may occur. Therefore, the restricting protrusions 135 restrict deformation of the sheet guide portion 136 so that the misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the tops of the guide ribs at the ends is 1 mm or less.

[0027] Furthermore, by restricting deformation of the sheet guide portion 136 with the restricting protrusion 135, it is possible to suppress relative misalignment in the X direction between this sheet guide portion 136 and another sheet guide in the re-supply path 36 adjacent to this sheet guide portion 136. This makes it possible to suppress the sheet from getting caught on the sheet guide portion 136 when it moves from the sheet guide on the upstream side in the conveying direction to the sheet guide portion 136. It is also possible to suppress the sheet from getting caught on the sheet guide portion 136 when it moves from the sheet guide portion 136 to the sheet guide on the downstream side in the conveying direction.

[0028] Furthermore, restricting deformation of the sheet guide portion 136 with the restricting protrusion 135 has the following advantages over restricting deformation of the sheet guide portion 136 on the opposing surface of the opposing portion 131a of the lower cover member 131. That is, when restricting deformation of the sheet guide portion 136 on the opposing surface of the sheet guide portion of the lower cover member 131, it is necessary to increase the positional accuracy in the X direction of the entire opposing surface. On the other hand, in the case of the restricting protrusion 135, it is sufficient to increase the positional accuracy in the X direction of only the restricting protrusion 135 (specifically, the convex portion 135a). Therefore, compared to restricting deformation of the sheet guide portion 136 on the opposing surface of the opposing portion 131a of the lower cover member 131, there are advantages in that dimensional accuracy is easier to achieve and the position of each guide rib in the X direction can be maintained with high precision.

[0029] Furthermore, by increasing the difference in height between the guide ribs at the center of the sheet guide portion 136 in the Y direction and the guide ribs at the ends in advance, it is possible to suppress misalignment in the X direction between the tops of the guide ribs at the center of the Y direction and the ends when the warping of the sheet guide portion 136 worsens due to the heat of the heating roller 32a. However, the warping of the sheet guide portion 136 is not uniform, and there are cases where the heat of the heating roller 32a hardly worsens the warping of the sheet guide portion 136. In that case, conversely, the tops of the guide ribs at the center of the Y direction will be more misaligned in the +X direction relative to the tops of the guide ribs at the ends, which could cause the sheet to bend in the direction opposite to the warping direction of the sheet guide portion.

[0030] On the other hand, by providing the restricting protrusion 135, it is possible to suppress misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the end portions when the warping of the sheet guide portion 136 worsens, without increasing the difference in height between the guide ribs at the center in the Y direction and the end portions. Therefore, even when the warping of the sheet guide portion due to the heat of the heating roller 32a hardly worsens, it is possible to suppress misalignment in the X direction between the tops of the guide ribs at the center in the Y direction and the end portions.

[0031] Furthermore, when the heat of the heating roller 32a worsens the warpage of the sheet guide portion 136, the restricting protrusion 135 comes into contact with the sheet guide portion 136 to restrict deformation of the sheet guide portion 136. Therefore, before the warpage of the sheet guide portion 136 worsens, the restricting protrusion 135 (convex portion 135a) is not in contact with the sheet guide portion 136. Therefore, when the upper cover member 132 is assembled to the fixing frame 133, the restricting protrusion 135 does not come into strong contact with the sheet guide portion 136. This makes it easy to assemble the upper cover member 132 to the fixing frame 133.

[0032] 2, in this embodiment, the restricting protrusion 135 is provided so as to face the sheet guide portion 136 on the downstream side in the assembly direction of the upper cover member 132 to the fixation frame 133. If the restricting protrusion 135 is located on the upstream side (+Z direction side) in the assembly direction of the upper cover member 132 to the fixation frame 133, there is a risk that the upper cover member 132 will be assembled to the fixation frame 133 while the restricting protrusion 135 slides on the sheet guide portion 136. As a result, sliding resistance may be generated, which may deteriorate the ease of assembly.

[0033] On the other hand, in this embodiment, at the beginning of assembling the upper cover member 132 to the fixation frame 133, the upper cover member 132 can be moved in the -Z direction with a sufficient gap between the sheet guide portion 136 and the fixation frame 133. This allows the upper cover member 132 to be easily moved in the -Z direction. Then, at the end of assembling, the position of the upper cover member 132 in the X direction in the figure is adjusted so that the side surface of the upper cover member 132 on the -X direction abuts against the fixation frame 133, and the upper cover member 132 is moved in the -Z direction. As a result, the restricting protrusion 135 faces the sheet guide portion 136, and the upper cover member 132 is assembled to the fixation frame 133. In this way, by having the restricting protrusion 135 face the sheet guide portion 136 on the downstream side (-Z direction side) of the assembling direction of the upper cover member 132 to the fixation frame 133, the ease of assembling the upper cover member can be improved compared to when the restricting protrusion 135 faces the sheet guide portion 136 on the upstream side.

[0034] In the above description, the guide ribs at the axial center are higher than the guide ribs at the ends. However, depending on the warpage of the sheet guide portion after molding, the heights of the guide ribs may be the same. In this case, however, the tolerance for worsening warpage of the sheet guide portion 136 due to the heat of the heating roller 32a is reduced. As a result, the gap between the restricting protrusion 135 and the sheet guide portion 136 before the warpage of the sheet guide portion 136 worsens becomes narrow, which may make it difficult to assemble the upper cover member 132.

[0035] On the other hand, by making the guide ribs at the axial center higher than the guide ribs at the ends, as in this embodiment, it is possible to increase the tolerance for worsening warpage of the sheet guide portion 136 due to the heat of the heating roller 32a. This makes it possible to widen the gap between the restricting protrusion 135 and the sheet guide portion 136 before the warpage of the sheet guide portion 136 worsens, and to suppress deterioration in the ease of assembling the upper cover member 132.

[0036] 4, the height H1 of the regulating protrusion 135 (two convex portions 135a) at the center in the Y direction may be made higher than the height H2 of the regulating protrusions 135 at the ends (H1>H2). When the warping of the sheet guide portion 136 worsens due to the heat of the heating roller 32a, the amount of deformation is greater at the center in the Y direction than at the ends. Therefore, by making the height H1 of the regulating protrusion 135 at the center in the Y direction higher than the height H2 of the regulating protrusions 135 at the ends, the effect of the regulating protrusion 135 in restricting deformation of the sheet guide portion 136 in the -X direction can be improved.

[0037] Furthermore, by providing restricting protrusions 135 at the Y-direction ends, even if the Y-direction ends of the sheet guide portion 136 are significantly deformed due to the heat of the heating roller 32a, the restricting protrusions 135 at the Y-direction ends can restrict the deformation of the sheet guide portion 136. This makes the sheet guide portion significantly convex, preventing the tops of the guide ribs in the center from shifting significantly in the +X direction relative to the tops of the guide ribs at the ends. Therefore, even if the Y-direction ends of the sheet guide portion 136 are significantly deformed due to the heat of the heating roller 32a, the positional accuracy of the tops of the guide ribs in the X direction can be maintained at a high level.

[0038] Also, the height H1 of the regulating projection 135 at the center in the Y direction and the height H2 of the regulating projection 135 at the end may be the same (H1 = H2). By making them the same, when the amount of deformation in the -X direction at the Y-direction end by the heating roller 32a is large and the sheet guide portion 136 abuts against all the regulating projections 135, the X-direction positions of the Y-direction end and the central portion can be made substantially the same. Therefore, when the heights of the respective guide ribs are the same, it is preferable that the positional deviation in the X direction at the tops of the guide ribs between the central portion and the end portion in the Y direction can be favorably suppressed.

[0039] Furthermore, when the height of the guide rib at the center in the Y direction is higher than the height of the guide rib at the end, the height H1 of the regulating projection 135 at the center in the Y direction may be lower than the height H2 of the regulating projection 135 at the end (H1 < H2). When the amount of deformation in the -X direction of the sheet guide portion 136 by the heating roller 32a is large and the sheet guide portion 136 abuts against all the regulating projections 135, the center in the Y direction of the sheet guide portion 136 can be recessed by the difference in the heights of the guide ribs 136a between the center and the end. Thereby, the positional deviation in the X direction at the tops of the guide ribs between the central portion and the end portion in the Y direction can be favorably suppressed.

[0040] Also, as shown in FIG. 5, the intervals in the axial direction (Y direction) of the regulating projections 135 may be unequal. In FIG. 5, the interval L3 between the regulating projections 135 near the center in the Y direction is narrower than the interval L2 between the regulating projections 135 at the end. Thus, by narrowing the interval between the regulating projections 135 at the center in the Y direction, the regulating force at the center can be increased. As described above, when the warping of the sheet guide portion 136 due to the heat of the heating roller 32a deteriorates, the amount of deformation at the center in the Y direction is larger than that at the end. Therefore, by narrowing the interval between the regulating projections 135 at the center in the Y direction to increase the regulating force at the center, the amount of deformation at the center in the Y direction of the sheet guide portion can be favorably regulated.

[0041] In the configuration shown in FIG. 5, by setting the heights H1, H2, and H3 of the respective regulating protrusions such that H1 > H2 > H3, the regulating effect of the deformation of the sheet guide portion 136 in the -X direction by the regulating protrusion 135 can be enhanced in the same manner as described above. Further, when the heights of the respective guide ribs 136a are the same, H1 = H2 = H3 may be set, or when the height of the guide rib 136a increases toward the center in the Y direction, H1 < H2 < H3 may be set.

[0042] Note that in the above description, the regulating protrusion 135 has a shape having two convex portions 135a, but the shape of the regulating protrusion 135 is not limited to this. For example, it may be appropriately set according to the ease of molding, etc., such as the shapes shown in FIGS. 6(a) to 6(d). Further, the number of the regulating protrusions 135 and the height of each regulating protrusion 135 are merely examples, and may be appropriately determined according to the manner of deformation of the sheet guide portion 136 due to the heat of the heating roller 32a, the amount of deformation, and the height of each guide rib. Further, the regulating protrusion 135 is not limited to the lower cover member 131, and may be provided on a member having a facing portion facing the sheet guide portion 136 on the side opposite to the sheet guide side of the sheet guide portion 136. Also, in the above description, the sheet guide portion 136 is provided on the upper cover member 132, but the sheet guide portion 136 may be provided on the lower cover member 131 and the regulating protrusion 135 may be provided on the upper cover member 132.

[0043] Note that in the above description, an image forming apparatus that outputs a monochrome image has been described, but the present invention can also be applied to an apparatus that has an image forming unit that forms toner images of Y, M, C, and K and forms a full-color toner image on a sheet.

[0044] The above description is merely an example, and each of the following aspects has a specific effect. (Aspect 1) In a fixing device 32 having a heating member such as a heating roller 32a that heats a sheet, a pressure member such as a pressure roller 32b that pressurizes a sheet passing through a nip portion formed by contacting the outer peripheral surface of the heating member, and a cover member such as an upper cover member 132 that covers the heating member and the pressure member, the cover member has a sheet guide portion 136 that guides the sheet, and a restricting protrusion 135 that restricts deformation of the sheet guide portion 136 is provided on an opposing portion facing the sheet guide portion 136. As a result, as described in the embodiment, deformation of the sheet guide portion 136 due to heat from a heating member such as the heating roller 32a can be restricted by the restricting protrusion 135. Furthermore, by using the restricting protrusion, it is easier to achieve positional accuracy compared to restricting deformation of the sheet guide portion 136 using the entire opposing surface of the opposing portion that faces the sheet guide portion 136. Therefore, the sheet guide position of the sheet guide portion 136 (in this embodiment, the position of the top of the guide rib) can be maintained with high accuracy compared to restricting deformation of the sheet guide portion 136 using the entire opposing surface.

[0045] (Aspect 2) In aspect 1, a heating member such as the heating roller 32a and a pressure member such as the pressure roller 32b are covered by a plurality of cover members (in this embodiment, a lower cover member 131 and an upper cover member 132), the sheet guide portion 136 has a predetermined gap d between it and a main body frame such as a fixing frame 133, the cover member such as the upper cover member 132 having the sheet guide portion 136 is made of resin, and the regulating protrusion 135 is provided on a cover member such as the lower cover member 131 that is separate from the cover member having the sheet guide portion 136. According to this, as described in the embodiment, by providing a predetermined gap d between the sheet guide section 136 and the fixing frame 133, it is possible to suppress the heat of a heating member such as the heating roller 32a from being transmitted to the sheet guide section 136 via a main body frame such as the fixing frame 133, and to suppress a rise in temperature of the sheet guide section 136. This makes it possible to suppress the toner image formed on the sheet from being heated by the sheet guide section, which would cause the toner in the toner image to re-melt and disrupt the image. When the cover member having the sheet guide portion is made of resin, the sheet guide portion may become concave due to warping during molding. Furthermore, providing a predetermined gap d between the sheet guide portion and the main frame may exacerbate the warping of the sheet guide portion due to heat from the heating element. However, in aspect 2, the restricting protrusion 135 provided on a cover member, such as the lower cover member 131, separate from the cover member having the sheet guide portion 136, restricts deformation of the sheet guide portion 136, thereby preventing the worsening of warping of the sheet guide portion due to heat from the heating element. This prevents relative misalignment in the sheet width direction between the sheet guide portion, which contacts the sheet and guides it, and allows the sheet guide portion to guide the sheet properly.

[0046] (Aspect 3) In the first or second embodiment, the direction in which a cover member such as upper cover member 132 is fastened to a main body frame such as fixing frame 133 is different from the direction in which sheet guide portion 136 is deformed. This makes it possible to improve the positional accuracy in a direction different from the deformation direction of the sheet guide portion (in this embodiment, the positional accuracy in the Z direction (sheet conveying direction)).

[0047] (Aspect 4) In any of the aspects 1 to 3, the restricting projection 135 faces the sheet guide portion 136 on the downstream side in the assembly direction of a cover member such as the upper cover member to a main body frame such as the fixing frame 133. This improves the ease of assembly of the cover member to the main body frame compared to when the regulating protrusion 135 faces the sheet guide portion 136 upstream in the assembly direction of the cover member, such as the upper cover member, to the main body frame, such as the fixing frame 133, as described in the embodiment.

[0048] (Aspect 5) In any one of the first to fourth aspects, the restricting protrusions 135 are provided in plurality. As a result, as described in the embodiment, the deformation of the sheet guide portion 136 can be regulated by multiple regulating protrusions 135, and the deformation of the sheet guide portion can be reduced compared to when the deformation of the sheet guide portion 136 is regulated by a single regulating protrusion 135.

[0049] (Aspect 6) In the fifth aspect, the plurality of restriction protrusions 135 are arranged side by side in the axial direction (Y direction), and the restriction protrusions on the central side in the axial direction are higher than the restriction protrusions on the end sides in the axial direction. As a result, as described in the embodiment, the amount of deformation of the axial center of the sheet guide portion due to heat from a heating member such as the heating roller 32a is greater than that at the ends, and therefore, by making the restricting protrusions at the axial center higher than the restricting protrusions at the axial ends, deformation of the sheet guide portion can be effectively suppressed.

[0050] (Aspect 7) In the fifth or sixth embodiment, the plurality of restriction protrusions 135 are arranged side by side in the axial direction, and the arrangement intervals of the restriction protrusions on the axial center side are different from the arrangement intervals of the restriction protrusions on the axial end side. As described in the embodiment, by varying the distance between the restricting protrusions 135 at the axial center of the sheet guide, where the amount of deformation due to heat from the heating member is large, and at the axial end portions, where the amount of deformation is small, it is possible to obtain a restricting force from the restricting protrusions according to the amount of deformation. This makes it possible to effectively suppress deformation of the sheet guide in the axial direction.

[0051] (Aspect 8) In the seventh aspect, the arrangement interval of the restriction protrusions on the axial center side is narrower than the arrangement interval of the restriction protrusions on the axial end side. As a result, as described in the embodiment, the regulating force of the regulating protrusion at the axial center of the sheet guide section, which is subject to a large amount of deformation in the axial direction due to the heat of the heating element, can be increased, and deformation at the axial center of the sheet guide section can be effectively suppressed.

[0052] (Aspect 9) In any of the first to eighth aspects, the sheet guide portion 136 has a plurality of guide ribs 136a arranged in the axial direction, with the guide ribs on the axially central side being higher than the guide ribs on the axially end sides. This allows for more accurate positional accuracy to be maintained than when the regulating protrusion alone is used to maintain the positional accuracy in the axial direction perpendicular to the sheet surface of the sheet guide of the sheet guide section, as described in the embodiment.

[0053] (Aspect 10) In any of the first to ninth aspects, the sheet guide section 136 guides the sheet in the reversing conveyance path such as the resupply path 36. This allows the distance between the reversing conveying path, such as the resupply path 36, and the fixing device to be narrowed, as described in the embodiment, thereby enabling the image forming apparatus to be made more compact. Also, jams in the reversing conveying path can be prevented.

[0054] (Aspect 11) In an image forming apparatus provided with a fixing device 32 that fixes a toner image carried on a sheet onto a recording material, the fixing device is provided with any one of the fixing devices of embodiments 1 to 10. This allows the image forming apparatus to be made smaller, and also prevents jams from occurring in the reverse transport path. [Explanation of symbols]

[0055] 32: Fixing device 32a: Heating roller 32b: Pressure roller 32c: Loading section 32d: Discharge section 33: Paper ejection roller 34: Paper ejection stack section 35: Reversing tray 36:Resupply route 131: Lower cover member 131a: opposing part 132: Upper cover member 133: Fixed frame 134: Screw 135: Regulating protrusion 136: Sheet guide section 136a: Guide rib 137: Pressure lever P: Seat d: Gap between the sheet guide and the fixing frame [Prior art documents] [Patent documents]

[0056] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-109676

Claims

1. a heating element for heating the sheet; a pressure member that presses the sheet passing through a nip portion formed by contacting an outer peripheral surface of the heating member; a fixing device including a cover member that covers the heating member and the pressure member, The fixing device is characterized in that the cover member has a sheet guide portion that guides the sheet, and a restricting protrusion that restricts deformation of the sheet guide portion is provided on an opposing portion that faces the sheet guide portion.

2. 2. The fixing device according to claim 1, the heating member and the pressure member are covered by a plurality of cover members, The sheet guide portion has a predetermined gap between itself and the main body frame, the cover member having the sheet guide portion is made of resin, The fixing device is characterized in that the regulating projection is provided on a cover member different from a cover member having the sheet guide portion.

3. 2. The fixing device according to claim 1, The fixing device according to claim 1, wherein the direction in which the cover member is fastened to the main body frame is different from the direction in which the sheet guide portion is deformed.

4. 2. The fixing device according to claim 1, The fixing device is characterized in that the regulating projection faces the sheet guide portion on the downstream side in the assembly direction of the cover member to the main body frame.

5. 2. The fixing device according to claim 1, The fixing device has a plurality of the regulating protrusions.

6. 6. The fixing device according to claim 5, A fixing device, characterized in that the plurality of regulating protrusions are arranged side by side in an axial direction, and the regulating protrusions on the central side in the axial direction are higher than the regulating protrusions on the end sides in the axial direction.

7. 7. The fixing device according to claim 5, A fixing device characterized in that the multiple regulating protrusions are arranged in a row in the axial direction, and the arrangement interval of the regulating protrusions on the center side of the axial direction is different from the arrangement interval of the regulating protrusions on the end side of the axial direction.

8. 8. The fixing device according to claim 7, The fixing device is characterized in that the arrangement interval of the regulating protrusions on the central side in the axial direction is narrower than the arrangement interval of the regulating protrusions on the end sides in the axial direction.

9. 2. The fixing device according to claim 1, The sheet guide portion has a plurality of guide ribs arranged in the axial direction, A fixing device, wherein the guide rib on the central side in the axial direction is higher than the guide ribs on the end sides in the axial direction.

10. 2. The fixing device according to claim 1, The fixing device is characterized in that the sheet guide portion guides the sheet on the reverse transport path.

11. In an image forming apparatus having a fixing device that fixes a toner image carried on a sheet onto a recording material, 10. An image forming apparatus comprising the fixing device according to claim 1 as the fixing device.

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