Fixing device

Abstract

The invention provides a new form of fixing device that builds upon conventional technology. [Solution] A fixing device comprising: an endless belt; a heater for heating the inner surface of the belt; a pressure roller including a roller portion that forms a nip portion for conveying a sheet together with the heater via the belt; and a frame made of resin that rotatably supports the pressure roller and faces the roller portion along the longitudinal direction of the pressure roller, wherein the frame includes a plurality of ribs arranged in the longitudinal direction of the pressure roller, and a plurality of ribs extending in a direction approaching the roller portion in a direction intersecting the longitudinal direction, the plurality of ribs including a first rib and a second rib provided in the longitudinal direction at a position further from the center of the roller portion than the first rib, and the distance between the tip of the second rib and the outer surface of the roller portion is greater than the distance between the tip of the first rib and the outer surface of the roller portion.

Description

Technical Field

[0001] The present invention relates to a fixing device provided in an electrophotographic image forming apparatus.

Background Art

[0002] The fixing device described in Patent Document 1 includes a heating unit having a heater that heats the inner surface of a belt, and a pressure roller that forms a nip portion together with the heater via the belt, and fixes the toner on the recording material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a new form of fixing device that develops conventional technology.

Means for Solving the Problems

[0005] One aspect of the present invention is as follows.

[0006] A fixing device for fixing an image on a sheet, comprising: An endless belt; A heater that heats the inner surface of the belt; A pressure roller including a roller portion that forms a nip portion for conveying the sheet together with the heater via the belt; A frame that rotatably supports the pressure roller and faces the roller portion over the longitudinal direction of the pressure roller, the frame being formed of resin; and The frame comprises a plurality of ribs arranged in the longitudinal direction of the pressure roller, including a plurality of ribs extending in a direction toward the roller portion in a direction intersecting the longitudinal direction. The plurality of ribs include a first rib and a second rib provided in the longitudinal direction at a position further from the center of the roller portion than the first rib, The distance between the tip of the second rib and the outer surface of the roller portion is greater than the distance between the tip of the first rib and the outer surface of the roller portion. A fixing device characterized by the following features. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a new form of fixing device that is an advancement of the conventional technology. [Brief explanation of the drawing]

[0008] [Figure 1] Cross-sectional view of the fixing device according to Example 1. [Figure 2] Cross-sectional view of the fixing device according to Example 1. [Figure 3] Cross-sectional view of the fixing device according to Example 1. [Figure 4] An exploded perspective view of the fixing device according to Example 1. [Figure 5] Front view and cross-sectional view (a, b, c, d) of the fixing device according to Example 1. [Figure 6] Cross-sectional views (a, b) of the fixing device according to Example 1. [Figure 7] An exploded perspective view of the fixing device according to Example 1. [Figure 8] A perspective view of the lower frame according to Example 1. [Figure 9] Cross-sectional view of the fixing device according to Example 1. [Figure 10] Plan view of the fixing device according to Example 1. [Figure 11] Plan view of the fixing device according to Example 1. [Figure 12] Plan view of the fixing device according to Example 2. [Figure 13] Plan view of the fixing device according to Example 3. [Figure 14] Plan view of the fixing device according to Embodiment 4. [Figure 15] Plan view of the fixing device according to Embodiment 5. [Figure 16] Plan view of the fixing device according to Embodiment 6.

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described based on the drawings. Note that dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments may be appropriately changed according to the configuration of the device to which the present invention is applied and various conditions. Therefore, unless otherwise specifically described, the scope of the present invention is not limited to this example.

[0010] FIG. 1 is a cross-sectional view of an electrophotographic image forming apparatus 1 to which a fixing device according to the present embodiment is applied. In the following description, as shown in FIG. 2, when the image forming apparatus 1 is installed on a horizontal plane, the vertical direction is defined as the Z direction. The direction intersecting the Z direction is defined as the Y direction. The Y direction is a direction parallel to the rotation axis direction of the pressing arm 652 described later. The direction intersecting both the Z direction and the Y direction is defined as the X direction. The X direction is a direction parallel to the direction in which the heating unit 61 described later conveys the recording material located at the nip portion. The X direction and the Y direction are preferably horizontal directions. Also, the X direction, the Y direction, and the Z direction preferably intersect each other orthogonally. Further, if necessary, the directions of the arrows X, Y, and Z shown in each drawing are respectively represented as the +X side, the +Y side, and the +Z side, and the opposite sides are respectively represented as the -X side, the -Y side, and the -Z side. In the following description, the direction in which the recording material is conveyed in the nip portion np1 described later is referred to as the recording material conveyance direction (+X direction). Also, the rotation axis direction of the pressing arm 652 described later is referred to as the axial direction. In the axial direction, the direction from the heating unit 61 described later toward the electrical contact 668b1 is referred to as the first axial direction (+Y direction). In the axial direction, the direction opposite to the first axial direction is referred to as the second axial direction (-Y direction). The Y direction is also the longitudinal direction of the heating unit 61 and the pressing rotating body 62, and in the following description, the longitudinal direction of the pressing rotating body 62 may be referred to as the roller longitudinal direction. Also, the Y direction is the generatrix direction of the belt 614.

[0011] <Example 1> The fixing device 6 in Example 1 will be described.

[0012] [Configuration of Image Forming Apparatus] The configuration of the image forming apparatus 1 will be described using FIG. 1. The image forming apparatus 1 includes an apparatus main body 2, a process cartridge 10, and a fixing device 6. The process cartridge 10 is detachably attached to the apparatus main body 2. The fixing device 6 is detachably attached to the apparatus main body 2. It can also be said that the fixing device 6 is mounted on the apparatus main body 2. Note that the fixing device 6 may be fixedly attached.

[0013] The main unit 2 of the apparatus comprises a paper feed tray 3, a sheet feeding unit 4, a transport path P, a transfer roller 51, a sheet discharge unit 7, a paper output tray 8, a laser scanner 9, and an opening / closing door 21. The process cartridge 10 comprises a photosensitive drum 11 and a developing roller 12 as a developer carrier. The process cartridge 10 also contains developer inside. The opening / closing door 21 is supported so as to be rotatable around a pivot axis 21a and is configured to move between a closed position that closes the opening 2a and an open position that opens the opening 2a. When the opening / closing door 21 is in the open position with the opening 2a open, the process cartridge 10 can be attached to and detached from the main unit 2 through the opening 2a.

[0014] The sheet feeding unit 4 consists of a paper feed roller 41, a separation roller 42, a separation pad 42a, and a transport roller pair 43. Based on the print start signal, the sheet S stored in the paper feed tray 3 is sent to the transport path P by the sheet feeding unit 4 and transported towards the transfer roller 51 via the registration roller pair 44.

[0015] When the sheet S is transported to a predetermined position, an image formation start signal is issued, and the image formation process begins. The photosensitive drum 11, which is rotated by a drive source (motor) (not shown), is uniformly charged to a predetermined potential by a charging means (not shown). The surface of the charged photosensitive drum 11 is exposed by a laser scanner 9 based on image information, and an electrostatic image is formed in which the charge of the exposed area is removed. The toner in the process cartridge 10 is carried on the developing roller 12 and supplied to the photosensitive drum 11 according to the electrostatic latent image, developing the latent image. As a result, the latent image is made visible on the photosensitive drum 11 as a toner image.

[0016] The transfer roller 51 is positioned opposite the photosensitive drum 11 of the process cartridge 10. When the sheet S, conveyed by the registration roller pair 44, passes through the nip between the photosensitive drum 11 and the transfer roller 51, a voltage is applied to the transfer roller 51 from the main unit 2 of the device, and the toner image on the photosensitive drum 11 is transferred to the sheet S as an unfixed image. Subsequently, the sheet S with the transferred toner image is conveyed to the fuser 6, which is equipped with a heating unit 61 and a pressurizing rotating body 62. The fuser 6 is a fixing device that fixes toner (developer) to the recording material. When the sheet S passes through the nip of the heating unit 61 and the pressurizing rotating body 62, the unfixed image transferred on the sheet S is heated and pressurized and fixed to the surface of the sheet S. The sheet S with the fixed toner image is discharged to the output tray 8 via the sheet discharge unit 7.

[0017] [Fuser configuration] Next, the configuration of the fuser unit will be described. Figure 2 is a plan view of the fuser unit 6. As shown in Figure 3, the heating unit 61 comprises a heater 611, a holder 612, a stay 613, and a belt 614. The heater 611 is provided on the inner surface side of the belt 614 and heats the belt 614. The heater 611 extends in the direction of the generatrix (Y direction) of the belt 614, and the shape of the heater 611 is flat. The heater 611 has a first surface 611a and a second surface 611b opposite to the first surface 611a, with the first surface 611a being supported by the holder 612. The second surface 611b faces the inner surface of the belt 614. The holder 612 is made of a heat-resistant resin such as PPS or liquid crystal polymer, and has a guide surface 612a and a support wall 612b. The guide surface 612a contacts the inner circumferential surface 614a of the belt 614 to guide the belt 614, and the support wall 612b has a support surface 612b1 that supports the heater 611. The support surface 612b1 of the support wall 612b is in contact with the first surface 611a of the heater 611. That is, since the support surface 612b1 supports the first surface 611a along the longitudinal direction of the pressurizing rotating body 62, the holder 612 can be called a heater support member.

[0018] The stay 613 is a member that supports the holder 612, and is formed by bending a plate material with greater rigidity than the holder 612, for example, a steel plate with a thickness of 1.6 mm, into a roughly U-shape.

[0019] The belt 614 is an endless belt that is heat-resistant and flexible, and is composed of, for example, a metal sleeve such as stainless steel coated with fluororesin, or a laminate of polyimide resin, silicone rubber, fluororesin, etc. A heater 611, a holder 612, and a stay 613 are arranged inside the belt 614, and the belt 614 is configured to rotate around these. The inner circumferential surface 614a of the belt 614 is in contact with the second surface 611b of the heater 611.

[0020] The pressurizing rotating body 62 (pressurizing roller) has a metal shaft 62a and a roller 62b made of an elastic material that covers the shaft 62a, and is pressed against the heater 611 via a belt 614. The pressurizing rotating body 62 sandwiches the belt 614 between itself and the heater 611, forming a nip portion np1 for nipping, heating, and pressurizing the sheet S. In other words, the pressurizing rotating body 62 (pressurizing roller) can be said to form a nip portion np1 together with the heater 611 via the belt 614. That is, the pressurizing rotating body 62 heats and pressurizes the sheet S together with the heater 611 at the nip portion np1.

[0021] The pressurized rotating body 62 is configured to rotate when a driving force is transmitted from a drive source provided by the image forming apparatus 1. As the pressurized rotating body 62 rotates, the belt 614 rotates in response. The sheet S on which the toner image has been transferred is transported between the pressurized rotating body 62 and the heated belt 614, thereby thermally fixing the toner image.

[0022] Next, the frame configuration of the fuser 6 will be described using Figure 3. Figure 3 is a plan view of the fuser 6. The fuser 6 has an upper frame 64 and a lower frame 63. The lower frame 63 can also be called the first frame and the upper frame 64 can be called the second frame. The lower frame 63 is the frame that supports the heating unit 61 and the pressurizing rotating body 62. The upper frame 64 is located above the lower frame 63 and covers the heating unit 61. The lower frame 63 and the upper frame 64 are resin members formed by non-conductive molded members (resin members). The upper frame 64 has an upper guide surface 64a located downstream of the heating unit 61 in the recording material transport direction (+X). The upper guide surface 64a guides the upper surface of the sheet S being transported in the recording material transport direction. The lower frame 63 has a lower guide surface 64a located downstream of the heating unit 61 in the recording material transport direction. The lower guide surface 64a guides the lower surface of the sheet S being transported in the recording material transport direction.

[0023] Next, the configuration of the lower frame 63 that supports the pressurized rotating body 62 will be described using Figure 4. Figure 4 is an exploded perspective view of the fuser 6. The lower frame 63 has rails 63b at its ends in the first axial direction and the second axial direction, respectively. The rails 63b extend vertically and support the holder 612 so that it can move vertically. The two rails 63b face each other in the axial direction. The rails 63b engage with grooves 617a1 and 617b1 provided on the transmission members 617a and 617b, respectively. The rails 63b are guide parts that guide the longitudinal end of the heating unit 61 so that the heating unit 61 can move in a direction toward the pressurized rotating body 62.

[0024] The fixing unit 6 is equipped with bearings 62c and 62d. The ends of the shaft 62a in the first axial direction and the ends in the second axial direction are supported by bearings 62c and 62d, respectively. Bearing 62c is positioned by fitting into a recess 63d1 provided in the lower frame 63. Similarly, bearing 62d is positioned by fitting into a recess 63d2 provided in the lower frame 63. The recesses 63d1 (groove) and 63d2 (groove) extend in the direction from the heating unit 61 toward the pressurizing rotating body 62 and are provided in the right wall portion 63w3 and the left wall portion 63w4, respectively. The recesses 63d1 (groove), 63d2 (groove), bearings 62c and 62d can be called roller support portions that support the longitudinal ends of the pressurizing rotating body 62. Bearing 62c is electrically conductive. In this configuration, the bearings 62c and 62d are provided with protrusions, and the lower frame 63 is provided with recesses 63d1 and 63D2, but the relationship between the protrusions and recesses may be reversed. Also, the means for fixing the bearings 62c and 62d to the lower frame 63 does not have to be of the protrusion-recess shape.

[0025] [Configuration of the pressurizing mechanism] Next, the configuration of the pressure mechanism of the fuser 6 will be described. Figure 5(a) is a front view of the fuser 6. Figures 5(b) to (d) are cross-sectional views of Figure 5(a), respectively.

[0026] As shown in Figure 5, the fuser 6 has a pressurizing mechanism 65 that presses the heating unit 61 against the pressurizing rotating body 62. The pressurizing mechanism 65 is provided at both the end of the lower frame 63 in the first axial direction and the end in the second axial direction. In other words, it can be said that the pressurizing mechanism 65 is supported by the lower frame 63. The structure of the pressurizing mechanism 65 provided on the end of the lower frame 63 in the first axial direction and the pressurizing mechanism 65 provided on the end of the lower frame 63 in the second axial direction are substantially the same. Therefore, the explanation of the pressurizing mechanism 65 provided on the first axial direction side also applies to the pressurizing mechanism 65 provided on the second axial direction side, so the explanation is omitted.

[0027] The pressurizing mechanism 65 includes a transmission member 651, a pressurizing arm 652, and a pressurizing spring 653. The pressurizing arm 652 is supported by a lower frame 63. More specifically, the pressurizing arm 652 is supported by a support portion 64d of the lower frame 63 and is rotatably supported around the central axis X1 of the support portion 64d. The support portion 64d is a substantially cylindrical projection.

[0028] The pressure arm 652 presses the transmission member 651 from above, moving the transmission member 651 downward. This causes the transmission member 651 to press the stay 613 downward. The transmission member 651 presses the stay 613, moving the stay 613 downward. As the stay 613 moves downward, the heating unit 61, which includes the stay 613, is pressed toward the pressure rotating body 62. The pressure spring 653 is a conductive tension coil spring that biases the pressure arm 652 so that the heating unit 61 is pressed toward the pressure rotating body 62. The pressure spring 653 engages with the lower frame 63 and the pressure arm 652. The biasing of the pressure arm 652 by the pressure spring 653 causes the pressure arm 652 to move the transmission member 651 downward. That is, the pressure arm 652 presses the heating unit 61 toward the pressure rotating body 62 (pressure roller).

[0029] [Configuration of the pressure release mechanism] Next, the configuration of the pressure release mechanism provided in the fuser 6 will be described using Figures 6 and 7. Figure 6 is a cross-sectional view of the fuser 6. Figure 6(a) shows the pressurized state with the pressure release mechanism 67 pressurized. Figure 6(b) shows the depressurized state with the pressure release mechanism 67 released. Figure 7 is an exploded perspective view of the upper frame 64, lower frame 63, and camshaft 671, with some parts such as the heating unit 61 and pressurizing rotating body 62 omitted. The pressure release mechanism 67 is a nip pressure release mechanism that changes the nip pressure in the nip section np1 between the heating unit 61 and the pressurizing rotating body 62. The pressure release mechanism 67 includes a camshaft 671 and a cam 672.

[0030] As shown in Figure 6, the camshaft 671 is rotatable about axis X2. The camshaft 671 extends axially and is made of a conductive metal. As shown in Figure 7, cams 672 are fixed (supported) to the first axial end and the second axial end of the camshaft 671, respectively. The cams 672 are supported so as to rotate together with the camshaft 671. The cams 672 are provided on the first axial end side and the second axial end side of the lower frame 63, respectively. The structure of the cam 672 provided on the first axial end side and the cam 672 provided on the second axial end side of the lower frame 63 are substantially the same.

[0031] The cam 672 presses against the pressurizing arm 652 against the biasing force of the pressurizing spring 653. That is, the rotation of the cam 672 changes the pressing force of the heating unit 61 against the pressurizing rotating body 62 by the pressurizing arm 652. The cam 672 is rotatable between the pressurizing position shown in Figure 6(a) and the release position shown in Figure 6(b).

[0032] To release the pressurized state, the camshaft 671 is rotated, causing the cam 672 to rotate. When the cam 672 rotates, the pressurizing arm 652, which is in contact with the cam 672, moves away from the transmission member 651 in the opposite direction to the direction in which the stay 613 is pressed against the transmission member 651. As a result, the pressure pressing the heating unit 61 toward the pressurizing rotating body 62 decreases.

[0033] Next, the support configuration of the camshaft 671 will be described using Figure 7. The lower frame 63 has a support wall 63l that rotatably supports the camshaft 671. The support wall 63l extends in the vertical direction (Z direction). The support wall 63l has a hole 631h that rotatably supports the camshaft 671. The camshaft 671 passes through the hole 631h. In other words, the support wall 63l can also be called a shaft support portion that supports the camshaft 671. The support wall 63l is provided on the end side in the first axial direction of the lower frame 63 and on the end side in the second axial direction of the lower frame 63. In addition, substantially the same hole 631h is provided in each support wall 63l.

[0034] The upper frame 64 has a support wall 64l that rotatably supports the camshaft 671. The support wall 64l extends vertically. The support wall 64l has a hole 641h that rotatably supports the camshaft 671. The camshaft 671 passes through the hole 641h. The support wall 64l is provided at the end of the upper frame 64 in the first axial direction and at the end of the lower frame 63 in the second axial direction. In addition, substantially the same hole 641h is provided in each support wall 64l.

[0035] [Structure of the lower frame] The configuration of the lower frame 63 will be explained using Figure 8. Figure 8 is a perspective view of the lower frame 63. The lower frame 63 comprises a base surface 63a, a front side wall portion 63w1, a rear side wall portion 63w2, a right side wall portion 63w3, and a left side wall portion 63w4. As shown in Figure 4, the base surface 63a is the surface that constitutes the upper end of the lower frame 63 and is the surface that faces the roller 62b along the longitudinal direction of the roller 62b. Reinforcement ribs 81 are provided on the base surface 63a. The reinforcement ribs 81 will be described later. The front side wall portion 63w1 is the downstream end of the lower frame 63 in the recording material transport direction (+X direction). The front side wall portion 63w1 extends in a direction that intersects both the longitudinal direction of the roller and the recording material transport direction. The -X direction side surface of the front side wall portion 63w1 is part of the base surface 63a. The rear side wall portion 63w2 is the upstream end of the lower frame 63 in the recording material transport direction. The rear wall portion 63w2 extends in a direction that intersects both the longitudinal direction of the roller and the recording material transport direction. The +X direction side of the rear wall portion 63w2 is part of the base surface 63a. The right side wall portion 63w3 is one side (+Y) end of the lower frame 63 in the longitudinal direction of the pressurizing rotating body 62. The right side wall portion 63w3 extends in a direction that intersects both the longitudinal direction of the roller and the recording material transport direction. The right side wall portion 64w3 is equipped with the rail 63b described above. The recess 63d1 described above is also formed in the right side wall portion 63w3. The right side wall portion 63w3 is connected to the +Y direction end of the base surface 63a. The left side wall portion 63w4 is the other side (-Y) end of the lower frame 63 in the longitudinal direction of the pressurizing rotating body 62. The left side wall portion 63w4 extends in a direction that intersects both the longitudinal direction of the roller and the recording material transport direction. The left wall portion 63w4 is equipped with the rail 63b described above. Furthermore, the left wall portion 63w4 has the recess 63d2 described above. The left wall portion 63w4 is connected to the -Y direction end of the base surface 63a.

[0036] Next, the through holes formed in the lower frame 63 will be explained using Figures 8 and 9. Figure 9 is a cross-sectional view of the fixing device 6. When the sheet S passes through the fixing nip np1, water vapor is generated from the sheet, and condensation may occur on the surface of the pressurizing rotating body 62. In this case, the frictional force between the pressurizing rotating body 62 and the sheet S decreases, and the sheet may slip, causing the image to be distorted. Also, paper wrinkles may occur. Therefore, in this embodiment, the occurrence of condensation is suppressed by providing through holes in the lower frame 63. The front side wall portion 63w1 has through openings 63w1h that penetrate from the base surface 63a to the outside. The through openings 63w1h are a plurality of through holes including through holes 63w1h1 to 63w1h6. The plurality of through holes are arranged along the longitudinal direction of the roller. In addition, each of the through holes 63w1h1 to 63w1h6 is provided between reinforcing ribs, which will be described later, in the longitudinal direction of the roller. A through-hole 63w2h is formed in the rear wall portion 63w2, penetrating from the base surface 63a to the outside. The through-hole 63w2h is a plurality of through-holes, including through-holes 63w2h1 to 63w2h6. The plurality of through-holes are arranged along the longitudinal direction of the roller. Furthermore, each of the through-holes 63w2h1 to 63w2h6 is provided between reinforcing ribs, which will be described later, in the longitudinal direction of the roller. As shown in Figure 9, the outer surface of the pressurized rotating body 62 is exposed to the outside of the fixing device through the through-hole 63w1h or the through-hole 63w2h. As described above, the formation of the through-holes 63w1h and 63w2h in the lower frame 63 suppresses the stagnation of air in the space housed in the lower frame 63 and suppresses the occurrence of condensation on the surface of the pressurized rotating body 62.

[0037] [Reinforcement ribs] Next, we will explain the reinforcing ribs 81 provided on the lower frame 63. First, we will explain the reason for providing the reinforcing ribs 81 using Figure 10. Figure 10 is a plan view showing the belt 614 and roller 62b, showing the state in which the recording material is being conveyed while being held in place by the nip portion np1. The sheet being conveyed to the fixing device 6 is conveyed such that the position of the center of the sheet in the longitudinal direction of the roller coincides with the position of the center of the nip portion np1. The fixing device 6 is capable of conveying multiple types of sheets with different widths in the longitudinal direction of the roller (Y direction). The fixing device 6 is capable of conveying a first-size sheet S1 which has the maximum width that can be conveyed by the nip portion np1 in the longitudinal direction of the roller. The fixing device 6 is also capable of conveying a second-size sheet S2 which is narrower than the first-size sheet S1. Figure 10(a) shows the case when the first-size sheet S1 passes through the nip portion np1. Figure 10(b) shows the case when the second-size sheet S2 passes through the nip portion np1. As shown in Figure 10(b), when the second-size sheet S2 passes through the nip section np1, the belt 614 and roller 62b (roller section) each include a passage region Rt1 through which the second-size sheet S2 passes. Also, when the second-size sheet S2 passes through the nip section np1, the belt 614 and roller 62b (roller section) each include a non-passage region Rt2 through which the second-size sheet S2 does not pass. In the non-passage region Rt2, no heat is absorbed due to the passage of the recording material, so the non-passage region Rt2 of the belt 614 and roller 62b may become excessively hotter than the passage region Rt1. This phenomenon is sometimes called heating of the non-passage region. If the temperature of the belt 614 and roller 62b is high, the heat emitted from the belt 614 and roller 62b may cause deformation of the lower frame 63, for example, creep deformation may occur. Furthermore, since the lower frame 63 in this embodiment is made of resin, it is more susceptible to deformation than a metal frame. Therefore, the fixing device 6 in this implementation is equipped with reinforcing ribs 81.

[0038] The configuration of the reinforcing rib 81 will be explained using Figure 8. The reinforcing rib 81 is a plurality of reinforcing ribs, including reinforcing ribs 810 and reinforcing ribs 820. Reinforcing rib 810 is a plurality of reinforcing ribs, including reinforcing ribs 810a to 810m. Reinforcing rib 820 is a plurality of reinforcing ribs, including reinforcing ribs 820a to 820f. In other words, reinforcing rib 81 has 19 reinforcing ribs, reinforcing rib 810 has 13 reinforcing ribs, and reinforcing rib 820 has 6 reinforcing ribs. The reinforcing rib 81 extends so as to protrude upward from the base surface 63a. That is, the reinforcing rib 81 extends in a direction that approaches the pressurizing rotating body 62 in a direction that intersects the longitudinal direction of the roller. Also, the reinforcing rib 81 is a plurality of ribs arranged in the longitudinal direction of the roller. Furthermore, as shown in Figure 9, when viewed in the longitudinal direction of the roller, the shape of the tip of the reinforcing rib 81 is an arc shape that follows the outer surface of the roller 62b. Note that the arc shape does not necessarily have to be a perfect arc, but may be a substantially arc shape. As shown in Figure 9, the nominal distance between the tip of the reinforcing rib 81 and the outer surface of the roller 62b is the same throughout the recording material transport direction.

[0039] Next, the arrangement relationship between the reinforcing ribs 81 and the pressurizing rotating body 62 will be explained using Figure 11. Figure 11 is a plan view of the fixing device 6. As shown in Figure 11, the reinforcing ribs 810b, 810d, 810f, 810h, 810j, and 810l are provided at positions that coincide with a part of the passage region Rt1 in the longitudinal direction of the roller. The reinforcing ribs 820a, 820c, 820d, and 820f are provided at positions that coincide with a part of the non-passage region Rt2 in the longitudinal direction of the roller. If any one of the reinforcing ribs 810b, 810d, 810f, 810h, 810j, and 810l is called the first rib, then it can be said that the first rib is provided at a position that coincides with a part of the passage region Rt1 in the longitudinal direction of the roller. Furthermore, if, for example, one of the reinforcing ribs 820a, 820c, 820d, and 820f is referred to as the second rib, then the second rib can be said to be located in the longitudinal direction of the roller, coinciding with a portion of the non-passing region Rt2. In other words, the second rib is located in the longitudinal direction of the roller, further from the center of the roller than the first rib.

[0040] In this embodiment, the pressurized rotating body 62 is a straight roller with a nominal outer diameter equal along its longitudinal direction, as shown by the solid line in Figure 11. In other words, the external shape of the pressurized rotating body 62 shown by the solid line in Figure 11 is the external shape when the pressure release mechanism 67 is in the pressure release state. The pressurized rotating body 62 shown by the dashed line in Figure 11 shows the shape of the pressurized rotating body 62 in the first state. In this embodiment, the first state is the state of the pressurized rotating body 62 6 hours after the image forming apparatus 1, on which the fixing device 6 is mounted, is placed in an environment with a temperature of 23 degrees Celsius and a humidity of 50%, and the power to the image forming apparatus 1 has been turned off. With the power to the image forming apparatus 1 turned off, no power is supplied to the heater 611. Also, in the first state, the pressure release mechanism 67 is in the pressurized state described above. When the pressurized rotating body 62 is in the first state, the distance between the surface of the pressurized rotating body 62 and the base surface 63a decreases as you move from the end of the pressurized rotating body 62 towards the center in the longitudinal direction of the pressurized rotating body 62. In the first state, the reason the pressurizing rotating body 62 has this shape is that, as shown in Figure 11, the holder 612 has a crown shape in which the width of the central part is longer than the width of the ends in the longitudinal direction of the roller. Furthermore, it can be said that the support surface 612b1 includes a region that curves so as it moves from the longitudinal end of the pressurizing rotating body 62 toward the center, it approaches the pressurizing roller.

[0041] In this embodiment, considering that the temperature of the roller 62b becomes higher at the edges than at the center due to the heating of the non-paper-feeding section, the first and second ribs are configured as follows: In the first state, the distance between the tip of the second rib and the outer surface of the roller 62b is greater than the distance between the tip of the first rib and the outer surface of the roller 62b (nominal dimension). More specifically, the height of the first rib from the base surface 63a (length of the first rib) is configured to be equal to the height of the second rib from the base surface 63a (length of the second rib) (nominal dimension). By configuring it in this way, the effect of heat on the second rib due to the heating of the non-paper-feeding section can be reduced.

[0042] In Example 1, the width of the first rib in the longitudinal direction of the roller is the same as the width of the second rib in the longitudinal direction of the roller (nominal dimension).

[0043] <Example 2> Next, Example 2 will be described. In Example 1, the pressurizing rotating body 62 was a straight roller, but in Example 2, the shape of the pressurizing rotating body 62 is an inverted crown shape in which the outer diameter increases from the center to the end in the longitudinal direction of the roller. It is an inverted crown shape. Also, in Example 1, the heights of the first rib and the second rib from the base surface 63a were the same in nominal dimensions, but in Example 2, the height of the second rib is smaller than the height of the first rib in nominal dimensions. Note that the distance between the outer surface of the roller 62b and the tip of the second rib is greater than the distance between the outer surface of the roller 62b and the tip of the first rib, which is the same as in Example 1. Similarly, the other configurations are the same as in Example 1, so their explanation will be omitted.

[0044] Example 2 will be described using Figure 12. Figure 12 is a plan view of the fixing device 6. The reason why the pressure rotating body 62 is in an inverted crown shape in this embodiment is to increase the paper transport speed at the fixing nip np1 at both longitudinal ends of the fixing nip np1, thereby generating a force that pulls the paper outward in the width direction, and reducing the occurrence of paper wrinkles.

[0045] The solid line in Figure 12 shows the external shape of the pressurizing rotating body 62 when the pressure release mechanism 67 is in the pressure release state. The dashed line in Figure 12 shows the shape of the pressurizing rotating body 62 in the first state described above. In Example 1, in the first state, the distance between the surface of the pressurizing rotating body 62 and the base surface 63a decreased as the pressurizing rotating body 62 moved from the end to the center in the longitudinal direction. However, in Example 2, since the pressurizing rotating body 62 has an inverted crown shape, the distance between the surface of the pressurizing rotating body 62 and the base surface 63a is, for example, the same from the end to the center in the longitudinal direction of the pressurizing rotating body 62. Therefore, if the height of the first rib and the second rib from the base surface 63a is the same as in Example 1, the distance between the outer surface of the roller 62b and the tip of the second rib becomes equal to the distance between the outer surface of the roller 62b and the tip of the first rib. Consequently, the second rib is affected by heat due to the heating of the non-paper-feeding section, and is therefore more prone to deformation than the first rib. Therefore, in this embodiment, the height of the second rib from the base surface 63a is made smaller than the height of the first rib from the base surface 63a (nominal dimension). With this configuration, the distance between the outer surface of the roller 62b and the tip of the second rib becomes larger than the distance between the outer surface of the roller 62b and the tip of the first rib.

[0046] As described above, the configuration of Example 2 reduces the occurrence of paper wrinkles due to the inverted crown shape, while also reducing the decrease in rigidity of the lower frame 63.

[0047] <Example 3> Next, we will describe Embodiment 3. This embodiment differs from Embodiment 1 in that the number of reinforcing ribs 820 located in the non-passing region Rt2 is greater. The other configurations are the same as in Embodiment 1, so we will omit further explanation. Figure 13 is a plan view of the fixing device 6. In the following description, any one of the reinforcing ribs 810 that are located in a position corresponding to a part of the passing region Rt1, are in a different position from the first rib in the longitudinal direction of the roller, and are adjacent to the first rib will be referred to as the third rib. Also, any one of the reinforcing ribs 820 that are located in a position corresponding to a part of the non-passing region Rt2, are in a different position from the second rib in the longitudinal direction of the roller, and are adjacent to the second rib will be referred to as the fourth rib. As shown in Figure 13, in this embodiment, the number of reinforcing ribs 820 is greater than in Embodiment 1, and the reinforcing ribs 820 are arranged more densely than in Embodiment 1. As a result, the distance between the second rib and the fourth rib in the longitudinal direction of the roller is smaller than the distance between the first rib and the third rib in the longitudinal direction of the roller. In this way, by densely arranging the reinforcing ribs 820 in the non-passing region Rt2, the effect of heat on the lower frame 63 due to the temperature rise in the non-passing section can be further reduced compared to Example 1.

[0048] <Example 4> Next, Example 3 will be described. This example differs from Example 1 in that the width of the reinforcing rib 820 located in the non-passing region Rt2 is larger. The configuration other than this point is the same as in Example 1. Figure 14 is a plan view of the fixing device 6. As shown in Figure 14, the width (thickness) of the reinforcing rib 820 (second rib) in the longitudinal direction of the roller is larger than the width (thickness) of the reinforcing rib 810 (first rib) in the longitudinal direction of the roller. By increasing the width (thickness) of the reinforcing rib 820 in this way, the effect of heat on the lower frame 63 due to the temperature rise of the non-passing section can be reduced more than in Example 1.

[0049] <Example 5> Next, Example 5 will be described. Figure 15 is a plan view of the fixing device 6. This example combines the configurations of Example 2, Example 3, and Example 4. Specifically, the shape of the pressurizing rotating body 62 is an inverted crown shape. In addition, the distance between adjacent reinforcing ribs 820 in the longitudinal direction of the roller is smaller than the distance between adjacent reinforcing ribs 810 in the longitudinal direction of the roller. Furthermore, the width of the reinforcing rib 820 (second rib) in the longitudinal direction of the roller is larger than the width of the reinforcing rib 810 (first rib) in the longitudinal direction of the roller. These configurations provide the effects of Examples 2 and 3 described above compared to the configuration of Example 1. In other words, in this example, the inverted crown shape reduces the occurrence of paper wrinkles, while further reducing the effect of heat on the lower frame 63 due to the temperature rise of the non-paper-feeding section.

[0050] <Example 6> Modification 1 will be explained using Figure 16. Figure 16 is a plan view of the fixing device 6. The difference from the configuration of Embodiment 1 is that the fixing device 6 in this modification has a shielding member 63c. The other configurations are the same as in Embodiment 1, so the explanation will be omitted. The opposing region (base surface 63a) of the frame that coincides with the non-passing region Rt2 of the roller 62b in the longitudinal direction of the roller is defined as the opposing region 63a1. The shielding member 63c is positioned between the roller 62b and the opposing region 63a1 and shields from heat from the pressurizing rotating body 62. In this way, by adding the shielding member 63 to the configuration of Embodiment 1, the effect of heat on the lower frame 63 due to the temperature rise of the non-passing section can be further reduced.

[0051] The shielding member 63c may be added to the fixing device 6 in Examples 2 to 6.

[0052] Note that the number, shape, and arrangement of the reinforcing ribs 80, 810, and 820 described in Examples 1 to 6 are examples only and may be modified as appropriate for reasons such as increasing the rigidity of the lower frame 63.

[0053] This embodiment includes the following configuration.

[0054] (Item 1) A fixing device for fixing an image onto a sheet, An endless belt, A heater for heating the inner surface of the belt, A pressure roller including a roller section that forms a nip section for conveying the sheet together with the heater via the belt, A frame that rotatably supports the pressure roller and faces the roller portion in the longitudinal direction of the pressure roller, the frame being made of resin, Equipped with, The frame comprises a plurality of ribs arranged in the longitudinal direction of the pressure roller, including a plurality of ribs extending in a direction toward the roller portion in a direction intersecting the longitudinal direction. The plurality of ribs include a first rib and a second rib provided in the longitudinal direction at a position further from the center of the roller portion than the first rib, The distance between the tip of the second rib and the outer surface of the roller portion is greater than the distance between the tip of the first rib and the outer surface of the roller portion. A fixing device characterized by the following features.

[0055] (Item 2) The frame has a base surface on which the first rib and the second rib are provided. The fixing device according to item 1, characterized in that, in a direction perpendicular to the longitudinal direction, the height of the second rib from the base surface is smaller than the height of the first rib from the base surface.

[0056] (Item 3) The fixing device according to item 1 or item 2, characterized in that the longitudinal thickness of the second rib is greater than the longitudinal thickness of the first rib.

[0057] (Item 4) The roller portion of the pressure roller includes, in the longitudinal direction, a passage region through which a second-size sheet, which is narrower than a first-size sheet having the maximum width that can be conveyed by the nip portion, passes, and a non-passage region through which the second-size sheet does not pass. The first rib is provided at a position in the longitudinal direction that coincides with a part of the passage region, The second rib is provided in the longitudinal direction at a position that coincides with a part of the non-pass region. A fixing device according to any one of items 1 to 3, characterized by the above.

[0058] (Item 5) The aforementioned multiple ribs are A third rib provided at a position that coincides with a part of the passage region and is at a position different from the first rib in the longitudinal direction, wherein the third rib is adjacent to the first rib in the longitudinal direction, A fourth rib provided at a position corresponding to a part of the non-pass region and at a position different from the second rib in the longitudinal direction, wherein the fourth rib is adjacent to the second rib in the longitudinal direction, Includes, The distance between the second rib and the fourth rib in the longitudinal direction is smaller than the distance between the first rib and the third rib in the longitudinal direction. A fixing device according to any one of items 1 to 4, characterized by the above.

[0059] (Item 6) The tip of the first rib, when viewed in the longitudinal direction, has an arc shape that follows the outer surface of the roller portion. The tip of the second rib, when viewed in the longitudinal direction, has an arc shape that follows the outer surface of the roller portion. A fixing device according to any one of items 1 to 5, characterized by the above.

[0060] (Item 7) It also features a pressure spring, When the unit including the heater and the belt is used as a heating unit, The frame has side wall portions extending in a direction perpendicular to the longitudinal direction at its longitudinal ends, The side wall portion includes a roller support portion that supports the longitudinal end of the pressure roller, and a guide portion that guides the longitudinal end of the heating unit so that the heating unit can move toward the pressure roller. The heating unit is pressed toward the pressure roller by the pressure spring, which biases the longitudinal end of the heating unit. A fixing device according to any one of items 1 to 6, characterized by the above.

[0061] (Item 8) The roller support portion and the guide portion are grooves provided in the side wall portion, The groove extends in the direction from the heating unit toward the pressure roller. The fixing device according to item 7, characterized by the features described herein.

[0062] (Item 9) The frame is provided with through holes between the first rib and the second rib in the longitudinal direction. A fixing device according to any one of items 1 to 8, characterized by the above.

[0063] (Item 10) The outer surface of the pressure roller is exposed to the outside of the fixing device through the through hole. The fixing device according to item 9, characterized in that it is a fixing device.

[0064] (Item 11) The frame has a shielding member that is positioned in the longitudinal direction to coincide with at least a portion of the non-passing region of the pressure roller and that faces at least a portion of the non-passing region of the pressure roller, thereby shielding the opposing region of the frame from the heat of the pressure roller. The fixing device described in item 4, characterized by the features described herein.

[0065] (Item 12) The roller portion of the pressure roller has a region in the longitudinal direction where the outer diameter increases from the center to the end. A fixing device according to any one of items 1 to 11, characterized by the features described herein.

[0066] (Item 13) The heater has a first surface facing the inner surface of the belt and a second surface opposite to the first surface. The fixing device has a heater support member having a support surface that supports the second surface along the longitudinal direction, The support surface includes a region that curves so as it moves from the longitudinal end toward the center, it approaches the pressure roller. The roller portion is straight with an equal outer diameter along its longitudinal direction. A fixing device according to any one of items 1 to 12, characterized by the features described herein. [Explanation of Symbols]

[0067] 6. Fixing device 614 Belt 611 Heater 62 Pressure rollers 63 Lower frame 81 Reinforcement Ribs

Claims

1. A fixing device for fixing an image onto a sheet, An endless belt, A heater for heating the inner surface of the belt, A pressure roller including a roller section that forms a nip section for conveying the sheet together with the heater via the belt, A frame that rotatably supports the pressure roller and faces the roller portion in the longitudinal direction of the pressure roller, the frame being made of resin, Equipped with, The frame comprises a plurality of ribs arranged in the longitudinal direction of the pressure roller, including a plurality of ribs extending in a direction toward the roller portion in a direction intersecting the longitudinal direction. The plurality of ribs include a first rib and a second rib provided in the longitudinal direction at a position further from the center of the roller portion than the first rib, The distance between the tip of the second rib and the outer surface of the roller portion is greater than the distance between the tip of the first rib and the outer surface of the roller portion. A fixing device characterized by the following features.

2. The frame has a base surface on which the first rib and the second rib are provided. The fixing device according to claim 1, characterized in that, in a direction perpendicular to the longitudinal direction, the height of the second rib from the base surface is smaller than the height of the first rib from the base surface.

3. The fixing device according to claim 1, characterized in that the longitudinal thickness of the second rib is greater than the longitudinal thickness of the first rib.

4. The roller portion of the pressure roller includes, in the longitudinal direction, a passage region through which a second-size sheet, which is narrower than a first-size sheet having the maximum width that can be conveyed by the nip portion, passes, and a non-passage region through which the second-size sheet does not pass. The first rib is provided at a position in the longitudinal direction that coincides with a part of the passage region, The second rib is provided in the longitudinal direction at a position that coincides with a part of the non-pass region. The fixing device according to feature 1.

5. The aforementioned multiple ribs are A third rib provided at a position that coincides with a part of the passage region and is at a position different from the first rib in the longitudinal direction, wherein the third rib is adjacent to the first rib in the longitudinal direction, A fourth rib provided at a position corresponding to a part of the non-pass region and at a position different from the second rib in the longitudinal direction, wherein the fourth rib is adjacent to the second rib in the longitudinal direction, Includes, The distance between the second rib and the fourth rib in the longitudinal direction is smaller than the distance between the first rib and the third rib in the longitudinal direction. The fixing device according to feature 4.

6. The tip of the first rib, when viewed in the longitudinal direction, has an arc shape that follows the outer surface of the roller portion. The tip of the second rib, when viewed in the longitudinal direction, has an arc shape that follows the outer surface of the roller portion. The fixing device according to feature 1.

7. It also features a pressure spring, When the unit including the heater and the belt is used as a heating unit, The frame has side wall portions extending in a direction perpendicular to the longitudinal direction at its longitudinal ends, The side wall portion includes a roller support portion that supports the longitudinal end of the pressure roller, and a guide portion that guides the longitudinal end of the heating unit so that the heating unit can move toward the pressure roller. The heating unit is pressed toward the pressure roller by the pressure spring, which biases the longitudinal end of the heating unit. The fixing device according to feature 1.

8. The roller support portion and the guide portion are grooves provided in the side wall portion, The groove extends in the direction from the heating unit toward the pressure roller. The fixing device according to feature 7.

9. The frame is provided with through holes between the first rib and the second rib in the longitudinal direction. The fixing device according to feature 1.

10. The outer surface of the pressure roller is exposed to the outside of the fixing device through the through hole. The fixing device according to feature 9.

11. The frame has a shielding member that is positioned in the longitudinal direction to coincide with at least a portion of the non-passing region of the pressure roller and that faces at least a portion of the non-passing region of the pressure roller, thereby shielding the opposing region of the frame from the heat of the pressure roller. The fixing device according to feature 4.

12. The roller portion of the pressure roller has a region in the longitudinal direction where the outer diameter increases from the center to the end. The fixing device according to feature 1.

13. The heater has a first surface facing the inner surface of the belt and a second surface opposite to the first surface. The fixing device has a heater support member having a support surface that supports the second surface along the longitudinal direction, The support surface includes a region that curves so as it moves from the longitudinal end toward the center, it approaches the pressure roller. The roller portion has a straight shape with an equal outer diameter along its longitudinal direction. The fixing device according to feature 1.

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