Fixing device and image forming apparatus

Abstract

To appropriately guide a medium to be fed.SOLUTION: A fixing device 22 of an image forming apparatus 1 has a heating roller 31 in a reverse crown shape, and is provided with a first portion 41 at the center of a guide inclined part 35S, a second portion 42 on an end side, and a third portion 43 at the center of the second part 42. In the guide inclined part 35S, a rear end portion of the first portion 41 is projected upward beyond a rear end portion of the second portion 42, and a rear end portion of the third portion 43 is located below the rear end portion of the second portion 42. The fixing device 22 can thus prevent the occurrence of wrinkles in, dirt on the back, and flip-up at a rear end of a sheet P conveyed from a developing device 10. The image forming apparatus 1 can thus prevent the occurrence of wrinkles in and dirt on the back of the sheet P and a reduction in image quality, and print a high-quality image on the sheet P.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to a fixing device and an image forming apparatus, and is suitable for application to, for example, an electrophotographic printer. [Background technology]

[0002] In recent years, there have been image forming apparatuses that print images by, for example, forming a toner image (also called a developer image) using toner (also called a developer) with a developing device, transferring the toner image (also called a developer image) to paper (also called a medium), and then fixing the image to the paper by applying heat and pressure with a fixing device. In addition, image forming apparatuses are appropriately provided with transport guides along the paper transport path that regulate the movement range of the paper.

[0003] Among these, the fixing device has rollers arranged above and below the paper transport path, and the paper is sandwiched in a nip formed between the two rollers, applying heat and pressure to the paper.Furthermore, some fixing devices have been proposed that provide a guide upstream of the nip to guide the paper, thereby ensuring that the paper reaches the nip properly and preventing wrinkles from occurring (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-65975 A (Fig. 1, etc.) Summary of the Invention [Problem to be solved by the invention]

[0005] However, due to various factors, the outer diameter of the roller in a fixing device can sometimes be larger at the ends than at the center. For example, while heat is absorbed by the paper at the center of the roller as it transports the paper, heat tends to remain at the ends. As a result, the roller's outer diameter may expand due to thermal expansion, and in this case, the outer diameter at the ends becomes slightly larger than at the center, resulting in a higher (faster) peripheral speed.

[0006] In addition, in a fixing device, for example, one of the rollers may be intentionally made larger in outer diameter at the end than at the center, giving it a shape known as an inverted crown, which will pull in the end of the paper more strongly than the center, thereby preventing wrinkles from occurring.

[0007] However, in a fixing device, if the outer diameter of the roller at the end is larger than that of the center, a portion of the paper may come into contact with the guide, resulting in a force acting on the paper that lifts the end (downstream) side. In this case, in an image forming apparatus, this force is suppressed while a portion of the paper is held by the developing device, but is released when the end of the paper is ejected from the developing device. In this case, the end of the paper and its vicinity may be suddenly lifted and collide with the transport guide, scattering the toner that forms the toner image transferred to the paper and significantly degrading image quality.

[0008] The present invention has been made in consideration of the above points, and aims to propose a fixing device and an image forming apparatus that can appropriately guide a medium that is fed. [Means for solving the problem]

[0009] In order to solve this problem, the fixing device of the present invention includes a first rotating body extending in a first direction, a second rotating body extending in the first direction and positioned to face the first rotating body in a second direction perpendicular to the first direction and to form a nip portion, and a guide portion positioned on the entrance side where the medium is fed into the nip portion and guiding the medium passing through a medium passing area at the entrance to the nip portion, the guide portion having a first portion including the center of the guide portion, a second portion on an end side, and a third portion between the first and second portions, within a range corresponding to the medium passing area in the first direction. a fourth portion between the first portion and the third portion in the first direction and protruding further than the third portion toward the medium passing region in the second direction; the first portion and the second portion protrude further toward the media passing region in the second direction than the third portion, and the length of the first portion protruding toward the media passing region in the second direction is longer than the length of the second portion protruding toward the media passing region. and the length by which the fourth portion protrudes toward the medium passing region in the second direction is shorter than the length by which the first portion protrudes. I did so. The fixing device of the present invention further includes a first rotating body extending in a first direction, a second rotating body extending in the first direction and positioned to face the first rotating body in a second direction perpendicular to the first direction and to form a nip portion, and a guide portion positioned on the entrance side of the nip portion where the medium is fed and guiding the medium passing through a medium passing area at the entrance to the nip portion, the guide portion having a first portion including the center of the guide portion, a second portion on the end side, and a third portion between the first and second portions, within a range corresponding to the medium passing area in the first direction, and In one of the rotating bodies, the outer diameter of the end portion in the first direction is larger than the outer diameter of the center in the first direction, the first and second portions protrude further toward the medium passing region than the third portion in the second direction, the length by which the first portion protrudes toward the medium passing region in the second direction is longer than the length by which the second portion protrudes toward the medium passing region, and the difference between the length by which the first portion protrudes relative to the third portion and the length by which the second portion protrudes relative to the third portion in the second direction is larger than the difference between the outer diameter of the center and the outer diameter of the end portion in at least one of the first rotating body and the second rotating body.

[0010] In addition, the image forming apparatus of the present invention is provided with a developing device that forms a developer image using developer and transfers it to a medium, the above-mentioned fixing device, and a transport guide that guides the medium between the developing device and the fixing device.

[0011] When a medium is fed into the entrance of the fixing device, the first portion of the guide section, which protrudes more than the second portion, lifts the center of the medium, thereby preventing wrinkles from occurring. Furthermore, the third portion, located between the first and second portions, is recessed more than the second portion, preventing the edge of the medium in the first direction from contacting the guide section. This prevents the end of the medium from bouncing up and colliding with surrounding components as soon as it is no longer clamped upstream. Furthermore, in the present invention, since the fourth portion protrudes more than the third portion between the first portion and the third portion, it is possible to prevent wrinkles from occurring in a medium that is relatively short in length in the first direction. [Effects of the Invention]

[0012] According to the present invention, it is possible to realize a fixing device and an image forming apparatus that can appropriately guide a medium that is fed therein. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. [Figure 2] FIG. 2 is a schematic perspective view showing the configuration of a fixing device. [Figure 3] FIG. 2 is a schematic front view illustrating the configuration of the fixing device. [Figure 4] 2 is a schematic cross-sectional view showing the A1-A2 cross section of the fixing device. FIG. [Figure 5] 2 is a schematic cross-sectional view showing a cross section taken along B1-B2 in the fixing device. FIG. [Figure 6] 3 is a schematic cross-sectional view showing a C1-C2 cross section of the fixing device. FIG. [Figure 7] 1 is a schematic diagram showing the arrangement of developing devices and a virtual fixing device in a virtual image forming apparatus, and the state of paper. [Figure 8] 10A and 10B are schematic diagrams showing a hypothetical developing device and the general shape of an inclined guide portion in the developing device and whether or not there is a problem. [Figure 9] 2 is a schematic diagram showing the arrangement of a developing device and a fixing device and the state of a sheet in the image forming apparatus according to the embodiment; [Figure 10] FIG. 2 is a schematic diagram illustrating the shape of a sheet of paper. [Figure 11] 10 is a schematic diagram showing the length of each part of the guide inclined portion. FIG. [Figure 12] 10 is a schematic diagram showing the results of a first verification. FIG. [Figure 13] 10 is a schematic diagram showing the results of a second verification. FIG. [Figure 14] 10 is a schematic diagram showing the results of a third verification. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0015] [1. Configuration of image forming device] As shown in the schematic side view of Figure 1, the image forming apparatus 1 is an electrophotographic printer that can form (i.e., print) a monochrome image on a medium, such as paper P. Incidentally, the image forming apparatus 1 does not have an image scanner function for reading a document or a communication function using a telephone line, and is a single-function SFP (Single Function Printer) that has only a printer function.

[0016] Image forming apparatus 1 has various components arranged inside a roughly box-shaped apparatus housing 2. In the following description, the right end portion in Fig. 1 is defined as the front of image forming apparatus 1, and the up-down direction, left-right direction, and front-rear direction are defined when viewed from the front. For convenience of explanation, the left-right direction will also be referred to as the width direction or first direction.

[0017] The image forming apparatus 1 is controlled as a whole by a control unit 3. This control unit 3 is connected to a host device such as a computer device (not shown), and when it receives a print instruction or print data from this host device, it executes an image forming process (also called a printing process) that forms a print image on the surface of paper P. At this time, the control unit 3 executes a predetermined conversion process based on the print data, for example, to generate image data to be supplied to a developing device (described later).

[0018] A paper cassette 5 that stores paper P is provided at the bottom inside the device housing 2. A paper feed conveying unit 6 is provided above and in front of the paper cassette 5. The paper feed conveying unit 6 forms a conveying path W (shown by a dashed line in the figure) along which the paper P is conveyed, using conveying guides that face each other at a predetermined distance. The conveying path W advances diagonally upward and forward from near the front end of the paper cassette 5, and then curves so as to head diagonally upward and rearward. The paper feed conveying unit 6 is provided with a plurality of rollers (some of which are not shown), such as registration rollers 7, and sensors (not shown) that detect the paper P, at predetermined locations along the conveying path W, as appropriate.

[0019] The paper feed conveyance unit 6 rotates each roller as appropriate based on the control of the control unit 3, thereby picking up and separating the paper sheets P stored in the paper cassette 5 one by one. The paper feed conveyance unit 6 also rotates each roller as appropriate to advance the paper sheets P along the conveyance path W and send them further backward.

[0020] A developing device 10 is disposed above the paper feed conveying section 6, and a transfer roller 11 is disposed below it, with a conveying path W passing between them being formed in a generally straight line along the front-to-rear direction. The developing device 10 has a photosensitive drum 12, a charging roller 13, an exposure section 14, a developer supply section 15, etc.

[0021] The photosensitive drum 12 is formed in a cylindrical shape along the left-right direction, and a charging layer made of a chargeable material is formed on its peripheral surface. The photosensitive drum 12 is rotatably supported and rotates clockwise in FIG. 1 by a driving force supplied from a driving force source (not shown). The charging roller 13 is formed in a cylindrical shape along the left-right direction and is rotatably supported. A predetermined high voltage is applied to the charging roller 13, and the charging roller 13 uniformly charges the contact point on the peripheral surface of the photosensitive drum 12.

[0022] The exposure unit 14 has multiple light sources such as LEDs (Light Emitting Diodes) and is also called an LED head. The exposure unit 14 exposes the peripheral side surface of the photosensitive drum 12 by causing each light source to emit light in a pattern based on image data supplied from the control unit 3, thereby changing the state of charge at the location irradiated with light. As a result, an electrostatic latent image based on the image data is formed on the peripheral side surface of the photosensitive drum 12.

[0023] The developer supply unit 15 has a developer storage section that stores toner as a developer, a supply roller (not shown) that supplies the toner, and the like, and supplies a thin film of toner to the circumferential surface of the photosensitive drum 12. As a result, the photosensitive drum 12 forms (i.e., develops) a toner image based on image data by causing the supplied toner to adhere to charged portions of the circumferential surface.

[0024] The transfer roller 11 is formed in a cylindrical shape extending in the left-right direction and is rotatably supported, with the vicinity of its upper end abutting the vicinity of the lower end of the photosensitive drum 12. A predetermined high voltage is applied to the transfer roller 11. When a sheet of paper P is transported along the transport path W with the developing device 10 and the transfer roller 11 rotating in a predetermined direction, the sheet of paper P is sandwiched between the photosensitive drum 12 and the transfer roller 11 and transported rearward, transferring a toner image onto the sheet of paper P. For convenience of explanation, hereinafter, toner will also be referred to as developer, and the toner image will also be referred to as developer image.

[0025] An intermediate conveying section 20 is provided behind the developing device 10, and a conveying path W is formed along the roughly front-to-rear direction. The intermediate conveying section 20 also has a conveying guide 21 above the conveying path W that regulates the movement range of the paper P. A fixing device 22 is provided behind the intermediate conveying section 20.

[0026] The fixing device 22 is provided with a rotatable heating roller 31, a pressure roller 32, etc. inside a fixing housing 30, and a fixing nip portion 22N is formed by bringing these rollers into contact with each other on the conveying path W (details will be described later). The fixing device 22 appropriately rotates the heating roller 31 and the pressure roller 32 to apply heat and pressure to the paper P in the fixing nip portion 22N, thereby fixing the toner image to the paper P and sending it rearward.

[0027] A paper discharge conveyance section 23 is disposed above and behind the fixing device 22. The paper discharge conveyance section 23 forms an arc-shaped conveyance path W using a paper discharge conveyance guide 24, a paper discharge conveyance roller 25, etc. The paper discharge conveyance section 23 advances the paper P along this conveyance path W in an upward and rearward diagonal direction, and then conveys the paper P in an upward and frontward diagonal direction, and discharges the paper P onto a discharge tray 26 formed on the top surface of the device housing 2 for placement thereon.

[0028] The image forming apparatus 1 is also provided with a double-sided printing mechanism 27. The double-sided printing mechanism 27 is provided with a switching unit that switches the transport path of the paper P, a transport mechanism that transports the paper P along a predetermined path, and a reversing mechanism that reverses the direction of travel of the paper P. After printing an image on one side of the paper P, the double-sided printing mechanism 27 reverses the direction of travel of the paper P and returns it to the front side of the developing device 10, so that an image can also be printed on the other side of the paper P. Thus, the image forming apparatus 1 can perform double-sided printing on the paper P in addition to single-sided printing.

[0029] In the following description, attention will be focused on the progress of the paper P on the transport path W, and the paper cassette 5 side on the transport path W will also be referred to as the upstream side, and the discharge tray 26 side will also be referred to as the downstream side.

[0030] [2. Configuration of the fixing device] Next, the configuration of the fixing device 22 will be described. FIG. 2 is a schematic perspective view of the fixing device 22. FIG. 3 is a schematic front view of the fixing device 22. FIG. 4(A) is a cross-sectional view taken along line A1-A2 in FIG. 3, and FIG. 4(B) is a partially enlarged view of that cross-sectional view. FIG. 5(A) is a cross-sectional view taken along line B1-B2 in FIG. 3, and FIG. 5(B) is a partially enlarged view of that cross-sectional view. FIG. 6(A) is a cross-sectional view taken along line C1-C2 in FIG. 3, and FIG. 6(B) is a partially enlarged view of that cross-sectional view.

[0031] The fixing device 22 is configured with multiple components incorporated inside a fixing housing 30 formed in the shape of a hollow rectangular parallelepiped. An inlet hole 33 is formed near the center of the front side of the fixing housing 30, penetrating the outside and inside of the fixing housing 30. Inside this inlet hole 33, a paper P (i.e., a medium) passes through an area surrounded by the inner surface (hereinafter referred to as a medium passing area 33P). Furthermore, an outlet hole 34 is formed near the center of the rear side of the fixing housing 30, penetrating the outside and inside of the fixing housing 30. Both the inlet hole 33 and the outlet hole 34 are formed in a rectangular shape that is long in the left-right direction and short in the up-down direction, allowing paper P with its surface oriented generally vertically to be easily inserted therethrough.

[0032] Inside the fixing housing 30, a heating roller 31 is disposed near the center, and a pressure roller 32 is disposed below it. The heating roller 31, which serves as a first rotating body, is configured as a cylinder centered on an imaginary central axis X31 along the left-right direction, and is configured to be rotatable about the central axis X31 by a support mechanism (not shown). In other words, the heating roller 31 is configured as a rotating body extending in the left-right direction. The heating roller 31 rotates clockwise in FIG. 4 and other figures by receiving a driving force from a fixing motor (not shown). A heating member 31H is incorporated inside the heating roller 31, and is configured to heat the heating roller 31 to a predetermined temperature.

[0033] Furthermore, the heating roller 31 has a so-called inverted crown shape, and the outer diameter gradually increases from the center to the ends in the left-right direction. Specifically, the radius of the heating roller 31 at the ends is 0.2 mm larger than the radius at the center.

[0034] The pressure roller 32, serving as a second rotating body, is cylindrically shaped with its center at an imaginary central axis X32 along the left-right direction, and is configured to be rotatable about the central axis X32 by a support mechanism (not shown). That is, the pressure roller 32 is configured as a rotating body extending in the left-right direction. The pressure roller 32 has an upper end that is biased toward the lower end of the heating roller 31 by a biasing portion (not shown). A fixing nip 22N is formed at the contact portion between the heating roller 31 and the pressure roller 32.

[0035] For convenience of explanation, hereinafter, in Figure 4 and other figures, the imaginary line connecting the central axis X31 and the central axis X32 will be referred to as the central axis connecting line Y1. This central axis connecting line Y1 is perpendicular to the central axis X31 and the central axis X32. Hereinafter, the direction along the central axis connecting line Y1 will also be referred to as the second direction. Furthermore, the imaginary line perpendicular to the central axis connecting line Y1 in the fixing nip portion 22N will be referred to as the nip extension line Z1 (Figure 4).

[0036] Furthermore, a guide section 35 that guides the paper P is provided below the entrance hole 33 on the front surface of the fixing housing 30 (FIGS. 2 and 3). The guide section 35 is broadly composed of a guide front section 35F that forms part of the front surface of the fixing housing 30, and a guide inclined section 35S that is connected to the upper end of the guide front section 35F and forms the inner surface of the entrance hole 33.

[0037] The guide portion 35 is configured to be generally symmetrical about a virtual center line XC (FIG. 3) that passes through the center of the inlet hole 33 in the left-right direction. Therefore, the following description will focus on the left side of the guide portion 35 when separated by the center line XC, and the description of the right side of the guide portion 35 will be omitted. Incidentally, the center line XC also coincides with the center of the paper P in the left-right direction as it is transported along the transport path W (FIG. 1).

[0038] The upper surface of the guide slope 35S is an inclined surface that connects the front lower side and the rear upper side as a whole. Furthermore, as shown in Figures 2 and 3, the left half of the guide slope 35S is divided into four parts in the left-right direction, forming a first part 41, a second part 42, a third part 43, and a fourth part 44.

[0039] The first portion 41 is the centralmost portion and protrudes upward from the nip extension line Z1 (FIG. 6), i.e., toward the medium passing area 33P inside the inlet hole 33, more than the surrounding portions. This first portion 41 is composed of a first flat portion 41P and multiple first protruding portions 41R (FIGS. 2 and 3). The first flat portion 41P is an inclined surface connecting the diagonally lower front side and the diagonally upper rear side, and has a slightly larger inclination angle with respect to the front-to-rear direction (i.e., the horizontal direction in three-dimensional space) than the nip extension line Z1 (FIG. 6).

[0040] The first protruding portion 41R is a portion that protrudes upward from the first flat portion 41P and is formed like a rib that extends generally along the front-to-rear direction. The ridge of the first protruding portion 41R is inclined relative to the first flat portion 41P, with its front end portion being at the same height as the first flat portion 41P, while its rear end portion is sufficiently higher than the first flat portion 41P and positioned sufficiently above the nip extension line Z1. That is, the inclination angle of the ridge of the first protruding portion 41R relative to the front-to-rear direction is greater than that of the first flat portion 41P and is also sufficiently greater relative to the nip extension line Z1 (FIG. 6B).

[0041] When guiding a sheet of paper P, the first portion 41 brings the ridge portion of each first protrusion 41R or a portion nearby into contact with the sheet of paper P. This reduces the contact resistance between the first portion 41 and the sheet of paper P, compared to when an inclined surface is provided that passes through the ridge portion of each first protrusion 41R. In the following description, the height of the rear end portion of the first protrusion 41R is considered to be the height of the first portion 41.

[0042] The second portion 42 is located at the endmost position in the left-right direction, i.e., the leftmost position in the left half of the guide inclined portion 35S, and its upper surface is formed flat. The inclination angle of the second portion 42 relative to the front-rear direction is slightly larger than the nip extension line Z1 but smaller than that of the first flat portion 41P (FIG. 5(B)). The front end of the second portion 42 is located at the same height as the front end of the first flat portion 41P. The rear end of the second portion 42 is located above the nip extension line Z1 and below the rear end of the first protrusion 41R.

[0043] In the inclined guide portion 35S, the distance H1 representing the vertical distance between the rear end of the second portion 42 and the rear end of the first protrusion 41R is, for example, 1.5 mm. That is, the distance H1 is greater than 0.2 mm, which is the difference between the radius of the center and the radius of the end of the heating roller 31.

[0044] The third portion 43 is located between the first portion 41 and the second portion 42, adjacent to the right side (i.e., the center) of the second portion 42. The third portion 43 is composed of a front third inclined portion 43S and a rear third horizontal portion 43L (FIGS. 2 and 3). The front third inclined portion 43S is an inclined surface inclined with respect to the horizontal direction, and the inclination angle and the height of the front end portion are the same as those of the second portion 42. In other words, the third inclined portion 43S forms an inclined surface that is continuous with the second portion 42.

[0045] The rear third horizontal portion 43L is a generally horizontal plane, and its front end is connected to the rear end of the third inclined portion 43S. Furthermore, the front end portion of the third horizontal portion 43L is located above the nip extension line Z1, but the rear end portion is located below the nip extension line Z1 (FIG. 5B).

[0046] The fourth portion 44 is located between the first portion 41 and the third portion 43, and has a flat upper surface. The fourth portion 44 has an inclined surface that is inclined relative to the horizontal direction, and the inclination angle and the height of the front end portion are the same as those of the second portion 42 and the third inclined portion 43S. In other words, the fourth portion 44 forms an inclined surface that is continuous with the third inclined portion 43S and the second portion 42. The height of the rear end portion of the fourth portion 44 is also the same as the height of the rear end portion of the second portion (FIG. 4).

[0047] In this way, the guide inclined portion 35S of the guide section 35 is provided with a first portion 41 to a fourth portion 44 separated in the left-right direction, and each of these portions has a slightly different inclination angle of the inclined surface, height of the rear end portion relative to the nip extension line Z1, and vertical relationship.

[0048] [3. Paper intake by the fixing device] Next, how the fixing device 22 takes in the paper P will be described, focusing on the shape of the guide inclined portion 35S in the guide portion 35.

[0049] [3-1. Paper intake in virtual fixing device] Here, four types of virtual fixing devices are assumed: 122, 222, 322, and 422. The virtual fixing devices 122, 222, 322, and 422 differ from the fixing device 22 according to the present embodiment in that they have virtual inclined guide portions 135S, 235S, 335S, and 435S, respectively, instead of the inclined guide portion 35S of the guide portion 35, but are otherwise configured in the same manner.

[0050] 7(A) is a schematic perspective view showing the heating roller 31, pressure roller 32, and virtual guide portion 135 in a virtual image forming apparatus 101 provided with a virtual fixing device 122, and the photosensitive drum 12 and transfer roller 11 of the developing device 10. This virtual image forming apparatus 101 differs from the image forming apparatus 1 in that it has a virtual inclined guide portion 135S of the virtual guide portion 135 in the virtual fixing device 122 instead of the inclined guide portion 35S of the guide portion 35 in the fixing device 22, but other parts are configured similarly.

[0051] Unlike the guide slope 35S (FIGS. 2 and 3) according to the present embodiment, the imaginary guide slope 135S has a uniform, flat inclined surface. The inclination angle and the height of the rear end portion of the imaginary guide slope 135S are the same as those of the second portion 42 and the fourth portion 44 according to the present embodiment.

[0052] In this virtual image forming device 101, the paper P is conveyed rearward while being sandwiched between the photosensitive drum 12 and the transfer roller 11 in the developing device 10, and a toner image is transferred onto the paper P. In the virtual image forming device 101, when the leading edge of the paper P eventually reaches the virtual fixing device 122, the vicinity of the leading edge of the paper P is guided by the virtual inclined guide portion 135S and is sandwiched between the heating roller 31 and the pressure roller 32. At this time, since the front and rear sides of the paper P are sandwiched, the portion between them is bent so as to protrude slightly downward due to the action of gravity, the low rigidity of the paper P, etc.

[0053] As described above, the heating roller 31 has an inverted crown shape, with the outer diameter at the ends being larger than that at the center. Therefore, the virtual fixing device 122 preferentially clamps the left and right ends of the leading edge of the paper P and pulls in the end portions at a higher speed than the center portion, which causes the paper P to be stretched in the left-right direction, thereby suppressing the occurrence of wrinkles to some extent.

[0054] Furthermore, in the virtual fixing device 122, the transport amount per unit time of the paper P (i.e., transport speed) is greater at the end portions than at the center portion in the left-right direction due to the shape of the heating roller 31. For this reason, the length of the portion of the paper P remaining in front of (i.e., upstream of) the virtual fixing device 122 is greater (longer) at the paper center portion PC in the left-right direction than at the paper end portion PE in the left-right direction.

[0055] 7(B) is a schematic side view showing the parts shown in FIG. 7(A) as viewed from the left side, and also shows the conveyance guide 21. As shown by the dashed lines in FIGS. 7(A) and (B), the paper P has a greater downward protrusion at the paper center PC than at the paper edge PE. Also, as shown in FIG. 7(A), the paper P is curved so that a virtual paper width direction line VPW extending along the width direction of the paper P protrudes downward immediately adjacent to the virtual fixing device 122.

[0056] As a result, when the paper P reaches the virtual fixing device 122, a portion of the paper P closer to the center than the paper edge PE comes into contact with the virtual inclined guide portion 135S, and an upward force acts on the portion of the paper P located in front of (upstream of) the virtual inclined guide portion 135S. However, because the front (upstream) portion of the paper P is sandwiched between the photosensitive drum 12 and the transfer roller 11 of the developing device 10, the paper P is not displaced upward and proceeds along a path that generally follows the conveyance path W (FIG. 1).

[0057] Eventually, in the virtual image forming device 101, as shown in FIG. 7(C) corresponding to FIG. 7(B), the trailing edge of the paper P, which is located on the most upstream side (hereinafter referred to as the trailing edge), leaves the developing device 10. At this time, in the virtual image forming device 101, the upward force of the paper P is released, which may cause the vicinity of the trailing edge to bounce upward and come into contact with the conveyance guide 21. As a result, in the virtual image forming device 101, the toner image that was transferred to the paper P but not fixed may become distorted, which may significantly reduce image quality.

[0058] In this way, in the virtual image forming device 101, the heating roller 31 of the virtual fixing device 122 is made in an inverted crown shape, and the peripheral speed at the end is higher than the peripheral speed at the center, which can suppress the occurrence of wrinkles, but there is a risk of image quality degradation due to the paper P bouncing up near the rear end.

[0059] Next, Fig. 8(A) shows schematic diagrams showing the height of the rear end portions of imaginary inclined guide portions 235S, 335S, and 435S, and of inclined guide portion 35S according to this embodiment, when viewed from the front, arranged side by side in the left-right direction. However, in Fig. 8(A), for simplicity's sake, the upper end portion of first portion 41 of inclined guide portion 35S is represented by a straight line connecting the rear end portions of first protrusion 41R (Figs. 2 and 3) in the left-right direction. The same applies to each imaginary inclined guide portion.

[0060] In the imaginary guide slope portion 235S, the imaginary first portion 241 at the center has the same height as the first portion 41 in the present embodiment. On the other hand, in the imaginary guide slope portion 235S, the imaginary second portion 242 on the end side has the same height as the second portion 42 in the present embodiment.

[0061] In the virtual fixing device 222 provided with this virtual guide inclined portion 235S, the virtual first portion 241 is higher than the virtual second portion 242 and is also sufficiently high relative to the nip extension line Z1, which effectively prevents wrinkles from occurring in the paper P. In addition, in the virtual fixing device 222, the height of the virtual first portion 241 relative to the virtual second portion 242 is appropriate, so that the virtual first portion 241 does not apply excessive force to the back surface of the paper P, and the back surface of the paper P does not become soiled (hereinafter referred to as "back surface soiling"). However, in the virtual fixing device 222, as in the case of the virtual fixing device 122 shown in FIG. 7, there is a risk that the end portion of the paper P will bounce up (hereinafter referred to as "end bounce") when it leaves the developing device 10.

[0062] In the imaginary guide inclined portion 335S, the central imaginary first portion 341 is higher than the first portion 41 and the imaginary first portion 241 in the present embodiment. On the other hand, in the imaginary guide inclined portion 335S, the end side imaginary second portion 342 has the same height as the second portion 42 and the imaginary second portion 242 in the present embodiment.

[0063] In the virtual fixing device 322 provided with this inclined imaginary guide portion 335S, the virtual first portion 341 is higher than the virtual second portion 342 and is sufficiently higher than the nip extension line Z1, which effectively prevents wrinkles from occurring. Furthermore, in the virtual fixing device 322, the virtual first portion 341 has a sufficient height relative to the virtual second portion 342, so the edge of the paper P is pulled away from the inclined imaginary guide portion 335S, preventing edge bounce. However, in the virtual fixing device 322, the virtual first portion 341 is excessively high relative to the virtual second portion 342, which increases the pressure applied to the paper P and may result in staining of the back surface.

[0064] In the imaginary inclined guide portion 435S, the imaginary first portion 441 in the center is lower than the first portion 41 in the present embodiment and has the same height as the second portion 42. On the other hand, in the imaginary inclined guide portion 435S, the imaginary second portion 442 on the end side is sufficiently lower than the second portion 42 in the present embodiment and is lower than the nip extension line Z1.

[0065] In the virtual fixing device 422 provided with this virtual guide inclined portion 435S, the virtual first portion 341 has a sufficient height relative to the virtual second portion 342, so that the edge of the paper P is pulled away from the virtual guide inclined portion 335S, thereby preventing end bounce. Furthermore, in the virtual fixing device 422, the height of the virtual first portion 441 relative to the virtual second portion 442 is appropriate, so there is no risk of rear surface contamination. However, in the virtual fixing device 422, the height of the virtual first portion 441 relative to the nip extension line Z1 is insufficient, so there is a possibility of wrinkles occurring.

[0066] 8B shows in table form a summary of the risk of occurrence of each of the problems of "wrinkles," "end jumping," and "backside contamination" in the hypothetical fixing devices 222, 322, and 422. In this table, the symbol "○" means that there is no risk of a problem occurring, and the symbol "×" means that there is a risk of a problem occurring. As can be seen from FIG. 8B, there is a risk of occurrence of any of "wrinkles," "end jumping," and "backside contamination" in any of the hypothetical fixing devices 222, 322, and 422.

[0067] [3-2. Paper intake in the fixing device according to this embodiment] Next, a case where paper P is taken in by the fixing device 22 (FIG. 2, etc.) according to this embodiment will be described. FIG. 9(A) corresponds to FIG. 7(A) and is a schematic perspective view showing the developing device 10, fixing device 22, paper P, etc. in the image forming apparatus 1 according to this embodiment. Note that, in FIG. 9(A), similar to FIG. 8(A), for simplification, the detailed shape of the first protrusion 41R (FIGS. 2 and 3) in the first part 41 of the guide inclined portion 35S is omitted.

[0068] In the image forming apparatus 1, the paper P is conveyed rearward while being sandwiched between the photosensitive drum 12 and the transfer roller 11 in the developing device 10, and a toner image is transferred onto the paper P. When the leading edge of the paper P eventually reaches the fixing device 22 in the image forming apparatus 1, the vicinity of the leading edge of the paper P is guided by the inclined guide portion 35S and is sandwiched between the heating roller 31 and the pressure roller 32. At this time, as in the case of the virtual image forming apparatus 101 (FIG. 7(A)), the paper P is sandwiched at both the front and rear sides, and therefore the portion between them is bent so as to protrude slightly downward due to the action of gravity, the low rigidity of the paper P, etc.

[0069] Furthermore, in the fixing device 22, as in the case of the virtual fixing device 122 (Figure 7(A)), the heating roller 31 has an inverted crown shape, and the outer diameter at the end is larger than the outer diameter at the center, which acts to stretch the paper P in the left-right direction, thereby suppressing the occurrence of wrinkles to some extent.

[0070] 9B corresponds to FIG. 7B and is a schematic side view showing the parts shown in FIG. 9A as viewed from the left side. As shown by the dashed lines in FIGS. 9A and 9B, the center PC of the paper P protrudes downward more than the edge PE. Also, as shown in FIG. 9A, the imaginary paper width direction line VPW of the paper P, which is aligned along the width direction of the paper P, curves downward in the vicinity of the fixing device 22.

[0071] However, in the fixing device 22, the rear end portion of the third horizontal portion 43L of the third portion 43 in the inclined guide portion 35S of the guide unit 35 is lower than the rear end portion of the second portion 42 and is lower than the nip extension line Z1. FIG. 9C is a schematic cross-sectional view of a virtual plane passing through the third portion 43 and normalized to the left and right. As can be seen from FIG. 9C, the paper P does not abut the inclined guide portion 35S at the third portion 43. Therefore, the paper P is hardly subjected to any upward force, as in the case of the virtual image forming device 101 (FIG. 7A). After that, in the image forming device 1, the trailing edge of the paper P leaves the developing device 10, but the vicinity of the trailing edge of the paper P does not bounce up.

[0072] 8A, the heights of the first portion 41 and the second portion 42 of the guide inclined portion 35S are equal to the heights of the imaginary first portion 241 and the imaginary second portion 242 of the imaginary guide inclined portion 235S. Therefore, the fixing device 22 having the guide inclined portion 35S can suppress the occurrence of wrinkles and backside contamination, similar to the case of the imaginary fixing device 222 having the imaginary guide inclined portion 235S. That is, the fixing device 22 according to this embodiment can suppress all of the problems of "wrinkles," "end jumping," and "backside contamination," as shown in FIG. 8B.

[0073] However, due to factors such as moisture absorption, the paper P may take on a shape that displaces vertically as it advances left and right, a so-called wavy shape, as shown in Fig. 10(A). In the fixing device 22, if the paper P advances to the fixing nip portion 22N (Fig. 4, etc.) in a wavy shape, there is a risk that the paper P will become wrinkled.

[0074] However, in the fixing device 22, as shown in Fig. 6(B) and elsewhere, the rear end portion of the first portion 41 is located above the nip extension line Z1. Therefore, when the leading edge of the sheet P is guided by the inclined guide portion 35S, the fixing device 22 brings the leading edge of the sheet P into contact with the circumferential side surface of the heating roller 31, and bends the leading edge diagonally downward and rearward as the heating roller 31 rotates clockwise. As a result, the leading edge of the sheet P is bent diagonally downward and rearward over the entire width of the sheet P, as shown in Fig. 10(B), eliminating any wavy shape along the left-right direction and suppressing the occurrence of wrinkles.

[0075] [3-3. Length of each part of the guide inclined section] Next, the length of each part of the guide inclined portion 35S will be described. First, the image forming apparatus 1 is designed to accommodate the short side of a maximum A3 size (420 x 297 mm) paper sheet P in the left-right direction (i.e., width direction). For this reason, the length of each part of the conveying path W formed inside the image forming apparatus 1 is set so that this A3 size paper sheet P can be conveyed with its short side facing the left-right direction and its long side aligned with the conveying direction. Hereinafter, this position will also be referred to as SEF (Short Edge Feed).

[0076] In the following description, A3 size SEF paper P is also referred to as the widest medium, and the length (297 mm) of the paper P in the left-right direction (i.e., width direction) is also referred to as the maximum width. Incidentally, in the fixing device 22 (FIGS. 2 and 3), the left-right length of the inlet hole 33, i.e., the left-right length of the guide inclined portion 35S, is 315 mm, which is slightly longer than the maximum width.

[0077] The image forming apparatus 1 is also capable of handling paper P smaller than A3 size, such as A4 size (297 x 210 mm). For example, when the image forming apparatus 1 handles A4 size paper as SFE, the length in the left-right direction (i.e., width direction) is 210 mm, which is shorter than the maximum width. Incidentally, the image forming apparatus 1 can also transport and print A4 size paper in a position where the long side faces the left-right direction and the short side is aligned with the transport direction (hereinafter referred to as LFE (Long Edge Feed)), in addition to the SFE position.

[0078] Fig. 11 shows a schematic representation of the shape of the guide inclined portion 35S when viewed from the front, and defines the symbols representing the lengths of each portion. Fig. 11 also shows a schematic cross-sectional shape of an A3-sized sheet P (hereinafter referred to as sheet P3) and an A4-sized sheet P in SEF (hereinafter referred to as sheet P4S or narrow-width medium).

[0079] Distance H2 represents the distance between the top end of the second portion 42 and the top end of the third portion 43 (i.e., the third horizontal portion 43L) in the up-down direction. Distance L1 represents the distance between the center ends of the third portion 43 on both sides of the center line XC in the left-right direction. Distance L2 represents the distance between the center ends of the second portion 42 on both sides of the center line XC in the left-right direction. Distance L3 represents the distance between the center end of the second portion 42 and the left-right end of the paper P3 in the left-right direction. This distance L3 is calculated by subtracting distance L2 from the length of the short side of A3-sized paper P3, i.e., the maximum width (297 mm), and then dividing the subtracted distance by two. Note that distance L3 is rounded to the nearest 0.1 mm to obtain an integer value.

[0080] Figure 12 is a table summarizing the results of an investigation into the occurrence of end splatter when distance H2 (Figure 11) was changed in four ways (hereinafter referred to as the first investigation). In this first investigation, A3-sized paper P3 with a basis weight of 67 gsm was used in a low-temperature, low-humidity environment (hereinafter referred to as the LL environment), where end splatter is relatively likely to occur. This first investigation also evaluated single-sided printing (denoted "Simp") and double-sided printing (denoted "Dup") cases. Furthermore, the values in Figure 12 represent the ratio of the number of sheets on which the problem (i.e., end splatter) occurred to the number of sheets evaluated in the first investigation, i.e., the problem occurrence rate, expressed as a fraction.

[0081] 12, in the first verification, when the distance H2 was 0.0 mm or 1.0 mm, the end bounce occurred frequently, but when the distance H2 was 1.5 mm or 2.0 mm, the number of end bounce occurrences was zero. Based on the results of this first verification, in the fixing device 22 according to this embodiment, the distance H2 is set to 1.5 mm. This 1.5 mm is sufficiently larger than the 0.2 mm difference between the radius of the center and the radius of the end of the heating roller 31 in the left-right direction.

[0082] Figure 13 is a table summarizing the results of an investigation into the occurrence of edge sagging and wrinkles when the distance L1 (Figure 11) was changed in four ways (hereinafter referred to as the second investigation). In this second investigation, edge sagging was investigated in an LL environment, and wrinkles were investigated in an LL environment as well as a high-temperature, high-humidity environment (hereinafter referred to as the HH environment). In addition to A3-size paper P3 with a basis weight of 67 gsm, A3-size paper P3 and SEF's A4-size paper P4S with a basis weight of 52 gsm were also used in the second investigation. Single-sided and double-sided printing were also evaluated. As with Figure 12, the values in Figure 13 represent the ratio of sheets with the problem (i.e., edge sagging or wrinkles) to the number of sheets evaluated in the second investigation, i.e., the problem occurrence rate, expressed as a fraction.

[0083] 13, in the second verification, problems occurred when the distance L1 was set to 120 mm or 180 mm, but the number of occurrences of each problem was zero when the distance L1 was set to 160 mm or 172 mm. For this reason, in the fixing device 22 according to the present embodiment, the distance L1 is set in the range from 160 mm to 172 mm.

[0084] Figure 14 is a table summarizing the results of an investigation into edge sagging and wrinkle occurrence when the distance L2 (Figure 11) was changed in nine ways (hereinafter referred to as the third investigation). In this third investigation, edge sagging was investigated in an LL environment, and wrinkle occurrence was investigated in both LL and HH environments. In addition, in the third investigation, A3-sized paper P3 with a basis weight of 60 [gsm] or 67 [gsm] was used, and evaluation was also conducted for single-sided and double-sided printing.

[0085] Furthermore, the numerical values shown in Figure 14 are the ratio of the number of sheets on which a problem (i.e., edge bounce or wrinkles) occurred to the number of sheets evaluated in the third verification, that is, the problem occurrence rate, expressed as a fraction, as in Figures 12 and 13. Note that blank spaces indicate that verification was omitted because it was estimated from the surrounding verification results that there was an extremely high possibility that a problem would not occur.

[0086] 14, in the third verification, problems occurred when the distance L2 was 228 mm or less or 279 mm or more, but the number of occurrences of each problem was zero when the distance L2 was 239 mm or more and 269 mm or less. For this reason, in the fixing device 22 according to the present embodiment, the distance L2 is set in the range of 239 mm or more and 269 mm or less, and accordingly the range of the distance L3 is set in the range of 14 mm or more and 29 mm or less.

[0087] Incidentally, when the distances L1, L3 and L4 are set to the above-mentioned values, the guide inclined portion 35S positions the left and right ends of the paper P3 on the second portion 42, and positions the left and right ends of the paper P4S, which has a smaller left and right (width) length than the paper P3, on the third portion 43.

[0088] Thus, by appropriately setting the length of each section of the guide inclined section 35S based on the results of each verification, problems such as end bouncing can be suppressed for paper P3, which is the largest size that can be printed, and SEF paper P4S, which has a shorter left-right length than paper P3.

[0089] [4. Effects, etc.] In the fixing device 22 of the image forming apparatus 1 according to the present embodiment, the heating roller 31 has an inverted crown shape, and the first portion 41 is provided at the center of the inclined guide portion 35S, the second portion 42 is provided at the end, and the third portion 43 is provided at the center of the second portion 42 (see FIG. 3, etc.). The inclined guide portion 35S positions the rear end portion of the second portion 42 above the nip extension line Z1, and the rear end portion of the first portion 41 protrudes above the rear end portion of the second portion 42. The inclined guide portion 35S also positions the rear end portion of the third portion 43 below the rear end portion of the second portion 42 and the nip extension line Z1 (see FIG. 8, etc.).

[0090] Therefore, when the paper P is conveyed from the developing device 10, the fixing device 22 can suppress the occurrence of wrinkles, prevent soiling of the back surface, and prevent the trailing edge from bouncing (FIGS. 8 and 9). As a result, the image forming apparatus 1 can print a high-quality image on the paper P without causing wrinkles or soiling of the back surface of the paper P, and without causing a deterioration in image quality due to the trailing edge bouncing.

[0091] From another perspective, none of the hypothetical fixing devices 122 (FIG. 7), 222, 322, and 422 (FIG. 8) could solve all three problems of wrinkles, backside contamination, and trailing edge bounce. In contrast, the fixing device 22 can solve all three problems by providing the third portion 43 in addition to the first portion 41 and the second portion 42 in the inclined guide portion 35S.

[0092] Furthermore, the distance L2 (FIG. 11) between the boundaries of the second portion 42 and the third portion 43 on the left and right sides of the guide inclined portion 35S is appropriately set based on the results of the third verification (FIG. 14). As a result, the fixing device 22 can appropriately prevent the occurrence of trailing edge bounce and wrinkles on the A3-sized paper P3.

[0093] Furthermore, the inclined guide portion 35S has a fourth portion 44 (FIG. 3, etc.) at the center of the third portion 43, the fourth portion 44 having the same height as the second portion 42, and the left-right distance L1 (FIG. 11) including the first portion 41 is appropriately set based on the results of the second verification (FIG. 13). This makes it possible for the fixing device 22 to suppress the occurrence of end bounce for the largest usable paper P3, and to prevent the occurrence of wrinkles for paper P4S that is shorter in the left-right direction than paper P3.

[0094] In addition, the inclined guide portion 35S has a distance H2 (FIG. 11), which is the upward protrusion distance of the first portion 41 relative to the second portion 42, appropriately set based on the results of the first verification (FIG. 12). This allows the fixing device 22 to appropriately suppress the occurrence of trailing edge bounce for A3-sized paper P3.

[0095] According to the above configuration, the fixing device 22 of the image forming apparatus 1 has an inverted crown-shaped heating roller 31, a first portion 41 at the center of the inclined guide portion 35S, a second portion 42 at the end, and a third portion 43 at the center of the second portion 42. The inclined guide portion 35S also has the rear end portion of the first portion 41 protrude higher than the rear end portion of the second portion 42, and the rear end portion of the third portion 43 positioned lower than the rear end portion of the second portion 42. This allows the fixing device 22 to prevent wrinkling, backside contamination, and rear-end bounce when the paper P is transported from the developing device 10. This allows the image forming apparatus 1 to prevent wrinkling and backside contamination in the paper P and a deterioration in image quality, thereby enabling high-quality images to be printed on the paper P.

[0096] 5. Other Embodiments In the above-described embodiment, the heating roller 31 of the fixing device 22 is described as having an inverted crown shape. However, the present invention is not limited to this. For example, at least one of the heating roller 31 and the pressure roller 32 may have an inverted crown shape. This effectively suppresses the occurrence of wrinkles. Alternatively, neither the heating roller 31 nor the pressure roller 32 may have an inverted crown shape, but may have a general cylindrical shape. In this configuration, for example, when printing images continuously on multiple sheets of paper P, the heat in the center of the heating roller 31 is absorbed by the sheets of paper P, causing the temperature in the center to drop more than the edge portions. As a result, the outer diameter of the edge portions may become larger than the outer diameter of the center portion due to thermal expansion. In this case, the same effects as when the heating roller 31 has an inverted crown shape can be obtained.

[0097] In the above-described embodiment, the height and inclination angle of the rear end portion of the fourth portion 44 of the guide inclined portion 35S are set to be the same as those of the second portion 42 (see FIG. 4, etc.). However, the present invention is not limited to this, and for example, the height and inclination angle of the rear end portion of the fourth portion 44 may be set to be different from those of the second portion 42. In this case, it is sufficient that the height of the rear end portion of the fourth portion 44 is at least lower than the rear end portion of the first protrusion 41R of the first portion 41.

[0098] Furthermore, in the above-described embodiment, the fourth portion 44 is provided in the inclined guide portion 35S (see FIG. 2, etc.). However, the present invention is not limited to this. For example, if the size of the paper P handled in the image forming apparatus 1, particularly the length in the width direction (i.e., the left-right direction), is one type, the fourth portion 44 may be omitted and the first portion 41 and the third portion 43 may be adjacent to each other. In this case, it is sufficient that the distances L2 and L3 are appropriately set based on the results of the third verification.

[0099] Furthermore, in the above-described embodiment, when the maximum width of the inclined guide portion 35S (FIG. 11) of the fixing device 22 is 297 mm, the distance L2 is set in the range of 239 mm to 269 mm, and the range of the distance L3 is set in the range of 14 mm to 29 mm. However, the present invention is not limited to this, and the distances L2 and L3 may be set appropriately depending on the maximum width of the paper P.

[0100] Furthermore, in the above-described embodiment, the difference between the center radius and the end radius of the heating roller 31 of the fixing device 22 is set to 0.2 mm, and the distance H1 representing the difference in height between the first portion 41 and the second portion 42 is set to 1.5 mm, which is larger than this difference. However, the present invention is not limited to this, and the distance H1 may be set to various values, such as 2.0 mm. Alternatively, the distance H1 may be set to be equal to or smaller than the difference between the center radius and the end radius of the heating roller 31.

[0101] Furthermore, in the above-described embodiment, the case where the rear end portion of the third portion 43 is positioned below the nip extension line Z1 in the inclined guide portion 35S of the fixing device 22 has been described (FIG. 5). However, the present invention is not limited to this, and for example, the rear end portion of the third portion 43 may be positioned above the nip extension line Z1.

[0102] Furthermore, in the above-described embodiment, the case where the rib-shaped first protrusion 41R is formed only on the first portion 41 of the inclined guide portion 35S of the fixing device 22 has been described (see FIG. 2, etc.). However, the present invention is not limited to this, and for example, a rib-shaped protrusion may be formed on at least a part of the second portion 42, the third portion 43, and the fourth portion 44. Alternatively, the first protrusion 41R may be omitted from the first portion 41, making it flat.

[0103] Furthermore, in the above-described embodiment, the heating roller 31 is disposed above the conveying path W, the heating roller 31 is configured as a hollow cylinder, and the heating member 31H is disposed inside the heating roller 31 (see FIG. 4, etc.). However, the present invention is not limited to this, and for example, the heating roller 31 may be configured as a cylinder like the pressure roller 32, and the heating member may be disposed near the outside of the heating roller 31. Furthermore, the heating roller 31 may be disposed below the conveying path W, and the pressure roller 32 may be disposed above the conveying path W.

[0104] Furthermore, in the above-described embodiment, a case has been described in which a single color image is printed by providing one developing device 10 in the image forming apparatus 1. However, the present invention is not limited to this, and for example, the image forming apparatus 1 may be provided with multiple developing devices 10 to print a color image by combining toners of multiple colors.

[0105] Furthermore, in the above-described embodiment, the image forming apparatus 1 is described as employing a direct transfer method in which the developing device 10 directly transfers the toner image onto the paper P. However, the present invention is not limited to this, and for example, the image forming apparatus 1 may be of an intermediate transfer method in which the developing device 10 transfers the toner image onto an intermediate transfer belt, and the toner image is then transferred from the intermediate transfer belt onto the paper P.

[0106] Furthermore, in the above-described embodiment, the image forming apparatus 1 is provided with a double-sided printing mechanism 27 to enable double-sided printing (FIG. 1). However, the present invention is not limited to this. For example, the double-sided printing mechanism 27 may be omitted from the image forming apparatus 1, enabling only single-sided printing. In this case, only single-sided printing needs to be evaluated in the first evaluation (FIG. 12), second evaluation (FIG. 13), and third evaluation (FIG. 14).

[0107] Furthermore, in the above-described embodiment, the present invention has been described as being applied to an image forming apparatus 1 having a printing function. However, the present invention is not limited to this, and may be applied to various devices having a printing function for a medium such as paper, such as a multifunction peripheral, a copying machine, or a facsimile machine.

[0108] Furthermore, the present invention is not limited to the above-described embodiments and other embodiments, and the scope of application of the present invention extends to embodiments in which the above-described embodiments and other embodiments are combined in part or in whole, or in which only a part of the above-described embodiments is extracted.

[0109] Furthermore, in the above-described embodiment, the fixing device 22 is configured by the heating roller 31 as the first rotating body, the pressure roller 32 as the second rotating body, and the guide inclined portion 35S as the guide portion. However, the present invention is not limited to this, and the fixing device may be configured by the first rotating body, the second rotating body, and the guide portion having various other configurations. [Industrial Applicability]

[0110] The present invention can be used in, for example, a fixing device that fixes a toner image on a sheet in an electrophotographic image forming apparatus. [Explanation of symbols]

[0111] 1...image forming apparatus, 10...developing device, 11...transfer roller, 12...photosensitive drum, 20...intermediate conveying section, 21...conveying guide, 22...fixing device, 22N...fixing nip section, 27...duplex printing mechanism section, 30...fixing housing, 31...heating roller, 32...pressure roller, 33...entrance hole, 33P...media passing area, 34...exit hole, 35...guide section, 35F...guide front section, 35S...guide inclined section, 41...first section, 42...second section, 43...third section, 43L... Third horizontal section, 43S...third inclined section, 44...fourth section, 101...virtual image forming device, 122, 222, 322, 422...virtual fixing device, 135...virtual guide section, 135S, 235S, 335S, 435S...virtual guide inclined section, 241, 341, 441...virtual first section, 242, 342, 442...virtual second section, 442...virtual second section, P, P3, P4S...paper, W...conveying path, X31, X32...central axis, Y1...central axis connecting line, Z1...nip extension line.

Claims

1. a first rotor extending in a first direction; a second rotating body extending in the first direction and disposed at a position facing the first rotating body in a second direction perpendicular to the first direction so as to be able to form a nip portion; a guide portion that is disposed on an entrance side where a medium is fed into the nip portion and that guides the medium passing through a medium passing area of the entrance to the nip portion; and The guide portion has a range corresponding to the medium passing area in the first direction. a first portion including a center of the guide portion; a second portion on the end side; a third portion between the first portion and the second portion; and a fourth portion between the first portion and the third portion in the first direction and protruding further than the third portion toward the medium passing region in the second direction; and the first portion and the second portion protrude further toward the medium passing region than the third portion in the second direction; a length of the first portion protruding toward the media passing region in the second direction is longer than a length of the second portion protruding toward the media passing region; The length by which the fourth portion protrudes toward the medium passing region in the second direction is shorter than the length by which the first portion protrudes. A fixing device characterized by:

2. the second portion is provided in a range in the first direction that includes an end position of a widest medium, which has a maximum length in the first direction among the media passing through the medium passing area, and The third portion is provided in a range in the first direction that includes the position of the end of a narrow-width medium whose length in the first direction is smaller than that of the widest-width medium.

2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a toner image onto a recording medium.

3. In the first direction, the distance between the end of the second portion on the central side and the end of the widest medium is 14 mm or more and 29 mm or less.

3. The fixing device according to claim 2, wherein the fixing device is a fixing device.

4. At least one of the first rotating body and the second rotating body is The outer diameter of the end portion in the first direction is larger than the outer diameter of the center in the first direction.

4. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

5. A difference between a length by which the first portion protrudes relative to the third portion and a length by which the second portion protrudes relative to the third portion in the second direction is a difference between the outer diameter of the center and the outer diameter of the end of at least one of the first rotating body and the second rotating body; 5. The fixing device according to claim 4.

6. the first portion and the second portion protrude toward the medium passing region with respect to a virtual nip extension line that is perpendicular to the second direction and passes through the nip portion, The third portion is recessed toward the opposite side of the media passing region with respect to the nip extension line.

6. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

7. A first rotating body extending in a first direction; a second rotating body extending in the first direction and disposed at a position facing the first rotating body in a second direction perpendicular to the first direction so as to be able to form a nip portion; a guide portion that is disposed on an entrance side where a medium is fed into the nip portion and that guides the medium passing through a medium passing area of the entrance to the nip portion; and The guide portion has a range corresponding to the medium passing area in the first direction. a first portion including a center of the guide portion; a second portion on the end side; a third portion between the first portion and the second portion; and and At least one of the first rotating body and the second rotating body has an outer diameter at the end portion in the first direction larger than an outer diameter at the center in the first direction, the first portion and the second portion protrude further toward the medium passing region than the third portion in the second direction; a length of the first portion protruding toward the media passing region in the second direction is longer than a length of the second portion protruding toward the media passing region; a difference between a length by which the first portion protrudes from the third portion and a length by which the second portion protrudes from the third portion in the second direction is greater than a difference between an outer diameter at the center and an outer diameter at the end of at least one of the first rotating body and the second rotating body; A fixing device characterized by:

8. a developing device that forms a developer image using a developer and transfers the developer image to the medium; The fixing device according to any one of claims 1 to 7, a conveyance guide that guides the medium between the developing device and the fixing device; An image forming apparatus comprising:

Images