Image forming apparatus

Abstract

To provide a configuration that supports a pre-fixing conveying unit 410 and a fixing unit 50 in a first housing 102a and a second housing 103a, respectively, and connects the first housing 102a and the second housing 103a with each other, and can prevent the occurrence of a failure in sheet conveyance.SOLUTION: The second housing 103a is connected to the first hosing 102a such that a part of the pre-fixing conveying unit 410 is inserted into the second housing, and thereby a sheet is conveyed from the pre-fixing conveying unit 410 to the fixing unit 50. The pre-fixing conveying unit 410 is oscillatably supported by an oscillating support part 415 with respect to the first housing 102a centered on an oscillation axis α along a sheet width direction intersecting a sheet conveyance direction FD. A positioning member 131a provided in the second housing 103a and a contact part 416 provided on a part of the pre-fixing conveying unit 410 are brought into contact with each other to determine the position of the pre-fixing conveying unit 410 in the oscillation direction centered on the oscillation axis α.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copier, printer, facsimile, or a multifunction machine having multiple functions of these. [Background technology]

[0002] In an image forming apparatus, a configuration in which a toner image is transferred to a sheet in a transfer unit and the toner image transferred to the sheet in the transfer unit is fixed to the sheet in a fixing unit has been conventionally known. Also, a configuration in which a conveying unit that conveys a sheet between the transfer unit and the fixing unit in the sheet conveying direction has been conventionally known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-83416 Summary of the Invention [Problem to be solved by the invention]

[0004] As image forming devices become faster, they are becoming larger, and some configurations support the conveying unit and the fixing unit in separate housings that are then connected together. In this configuration, many components are interposed between the conveying unit and the fixing unit, which are supported in separate housings, increasing the tolerance between the positions of the conveying unit and the fixing unit. This can cause the relationship between the positions of the conveying unit and the fixing unit to deviate from the appropriate position, potentially resulting in poor sheet transport when the sheet is transported from the conveying unit to the fixing unit.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration in which a conveying unit and a fixing unit are supported in separate housings and these housings are connected together, and in which occurrence of sheet conveyance problems can be suppressed. [Means for solving the problem]

[0006] The image forming apparatus of the present invention is characterized by comprising: a transfer unit that transfers a toner image onto a sheet; a fixing unit that fixes the toner image transferred onto the sheet by the transfer unit onto the sheet; a transport unit that is arranged between the transfer unit and the fixing unit in the sheet transport direction and transports the sheet toward the fixing unit; a first housing that supports the transport unit; a second housing that supports the fixing unit and is connected to the first housing so that a portion of the transport unit enters the second housing, thereby transporting the sheet from the transport unit to the fixing unit; a swing support unit that supports the transport unit so that it can swing freely relative to the first housing around a swing axis along the sheet width direction that intersects the sheet transport direction; and a positioning member that is provided on the second housing and abuts against an abutment portion provided on a portion of the transport unit, thereby positioning the transport unit in the swing direction around the swing axis. [Effects of the Invention]

[0007] According to the present invention, in a configuration in which the conveying unit and the fixing unit are supported in separate housings and these housings are connected, it is possible to suppress the occurrence of sheet conveyance problems. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] 1 is a cross-sectional view showing a schematic configuration of a main body of an image forming apparatus according to a first embodiment. [Figure 3] 1A is a schematic cross-sectional view of a color image forming station according to the first embodiment, and FIG. 1B is a schematic cross-sectional view of a black image forming station according to the first embodiment. [Figure 4] FIG. 2 is a cross-sectional view showing the schematic configuration of a fixing and conveying unit according to the first embodiment. [Figure 5] 1 is a schematic cross-sectional view showing a configuration from a secondary transfer unit in a main body of an image forming apparatus according to a first embodiment to a fixing unit in a fixing and conveying unit. [Figure 6] FIG. 2 is a schematic plan view of the pre-fixing transport section according to the first embodiment, seen from below. [Figure 7]FIG. 2 is a cross-sectional view showing a schematic configuration of a positioning unit according to the first embodiment, as viewed from the transport direction. [Figure 8] FIG. 2 is a schematic cross-sectional view showing a configuration for positioning a pre-fixing conveyance section according to the first embodiment. [Figure 9] FIG. 10 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a second embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing a schematic configuration from a secondary transfer unit in a main body of an image forming apparatus according to a second embodiment to a fixing unit in a fixing and conveying unit. [Figure 11] FIG. 10 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a third embodiment. [Figure 12] FIG. 11 is a schematic cross-sectional view showing the configuration from a secondary transfer unit in a main body of an image forming apparatus according to a third embodiment to a fixing unit in a fixing and conveying unit. DETAILED DESCRIPTION OF THE INVENTION

[0009] First Embodiment The first embodiment will be described with reference to Figures 1 to 8. First, the schematic configuration of an image forming apparatus (image forming system) of this embodiment will be described with reference to Figure 1.

[0010] [Image forming equipment] 1 is a schematic cross-sectional view of an image forming apparatus 100 including an image forming apparatus main body 101 according to this embodiment. The image forming apparatus main body 101 is composed of an image forming unit 102 that transfers a toner image onto a fed sheet S, and a fixing and conveying unit 103 that fixes the transferred toner image onto the sheet S. The image forming unit 102 and the fixing and conveying unit 103 are each composed of an independent housing. With this configuration, even a large apparatus can be packaged and transported in a separated state for each housing, improving the workability during logistics up to installation.

[0011] An original reading device 104 for reading an original image and an original feeding device 105 for feeding a plurality of stacked originals to the original reading device 104 one by one are selectively connected to the upper part of the image forming unit 102 .

[0012] On the upstream side of the image forming unit 102 in the conveying direction of the sheets S (hereinafter referred to as the sheet conveying direction), any one of a large-capacity feeding device 106 having a storage section for a plurality of sheets S, a manual feeding device (not shown), or a long-length feeding device (not shown) capable of accommodating long sheets S can be selectively connected. Further upstream of the large-capacity feeding device 106, any one of a large-capacity feeding device, a manual feeding device, and a long-length feeding device (not shown) can be selectively connected in a cascade.

[0013] A sensing device 107 is selectively connected downstream in the sheet conveying direction of the fixing and conveying unit 103 to read the fixed toner image formed on one or both sides of the sheet S, detect image density and image position deviation, and perform feedback correction on the image signal transmitted to the image forming unit 102. Further downstream of the fixing and conveying unit 103 or the sensing device 107, various sheet processing devices (not shown) such as an inserter, puncher, case binder, large-capacity stacker, folder, finisher, trimmer, etc. can be selectively connected alone or in combination.

[0014] As described above, the image forming apparatus main body 101 of this embodiment can be selectively connected to a variety of optional devices, making it possible to inline output products that have undergone a variety of post-processing processes on a variety of materials, thereby providing an image forming apparatus (image forming system) 100 that is highly productive, has high image quality, is highly stable, and has excellent functionality.

[0015] [Image forming section] Next, the schematic configuration of the image forming unit 102 will be described with reference to Figures 2, 3(a), and 3(b). Figure 2 is a schematic cross-sectional view of the image forming unit 102 in the image forming apparatus main body 101. Figure 3(a) is a schematic cross-sectional view showing the image forming stations 200Y, 200M, and 200C for yellow (Y), magenta (M), and cyan (C), respectively, and Figure 3(b) is a schematic cross-sectional view showing the black (K) image forming station 200K. Note that Figure 3(a) shows the yellow image forming station 200Y as a representative.

[0016] 2, image forming unit 102 includes multiple image forming stations 200Y, 200M, 200C, and 200K that form different toner images for each color: yellow (Y), magenta (M), cyan (C), and black (K). Note that the basic configuration of each color image forming station is the same, and therefore, hereinafter, the yellow image forming station 200Y will be described as a representative color image forming station. The only difference between the color image forming stations and the black image forming station is the size of the photosensitive drum, and the basic configuration for forming images is the same.

[0017] The surfaces of photosensitive drums 201Y and 201K, which serve as image carriers and photosensitive bodies, are uniformly charged by primary chargers 202Y and 202K, and then electrostatic latent images are formed by laser scanners 203Y and 203K, which are driven based on transmitted image information signals. In this embodiment, the primary charger 202Y for each color is a charging roller that is placed in contact with or close to the photosensitive drum 201Y, and the primary charger 202K for black is a corona charger, but the primary chargers may be either charging rollers or corona chargers.

[0018] The latent images formed on the photosensitive drums 201Y and 201K are developed into toner images by developing units 204Y and 204K. Toner consumed during development is appropriately replenished to the developing units 204Y and 204K from toner bottles 205Y and 205K via toner supply paths 206Y and 206K. The toner images on the photosensitive drums 201Y and 201K are sequentially transferred onto the intermediate transfer belt 208 by primary transfer rollers 207Y and 207K, applying a predetermined pressure and electrostatic load bias. After transfer, the small amount of residual toner remaining on the photosensitive drums 201Y and 201K is removed by photosensitive drum cleaners 209Y and 209K to prepare for the next image formation. The removed residual toner is collected in a recovered toner container 211 via a toner recovery path 210.

[0019] Meanwhile, sheets S fed one by one from a storage unit 212 for sheets S inside the image forming unit 102 or from one of the aforementioned externally connected paper feeders are looped by having their leading edges follow the nip portion of the registration rollers 213, thereby correcting skew. Thereafter, the registration rollers 213 convey the sheets S to the secondary transfer unit in synchronization with the toner image on the intermediate transfer belt 208. The outer secondary transfer roller 215 presses against the intermediate transfer belt 208, which is supported from the inside of the intermediate transfer belt 125 by the inner secondary transfer roller 214, to form a secondary transfer nip portion N1 between the outer secondary transfer roller 215 and the intermediate transfer belt 208.

[0020] The toner image on the intermediate transfer belt 208 is transferred to the sheet S at the secondary transfer nip N1 by applying a predetermined pressure and an electrostatic load bias. The secondary transfer inner roller 214, the intermediate transfer belt 208, and the secondary transfer outer roller 215 constitute a secondary transfer unit serving as a transfer unit in this embodiment. After transfer, the small amount of residual toner remaining on the intermediate transfer belt 208 is removed by an intermediate transfer belt cleaner 216 to prepare for the next image formation. The removed residual toner is collected in a recovered toner container 211 via a toner recovery path 210. The sheet S onto which the toner image has been transferred is transported downstream to the fixing transport unit 103 by a pre-fixing transport unit 410 serving as a transport unit.

[0021] [Fixing conveyance section] 4 is a schematic cross-sectional view of a fixing / conveying unit 103 in an image forming apparatus main body 101 according to this embodiment. The fixing unit (fixing device) 50 shown in FIG. 4 includes a heating roller 51 as a first rotating body having a heater 51a therein as a heat source, and an opposing roller 52 as a second rotating body arranged to be able to contact the heating roller 51 and forming a fixing nip N2 between the heating roller 51 and the opposing roller 52 for nipping and conveying a sheet. The fixing unit 50 fixes a toner image on the sheet S conveyed from the image forming unit 102 to the fixing nip N2 by applying heat and pressure. The sheet S heated by the fixing unit 50 is cooled by heat absorption by a heat sink 303 disposed inside a cooler 302, and is then discharged via a discharge / conveying path 304 to the sensing device 107 or a sheet processing device (not shown).

[0022] When the sheet S is to be discharged with its front and back sides reversed, the sheet S is switched back and conveyed in a double-sided reversing unit 306, and the sheet S is discharged in an inverted state by exchanging the leading and trailing ends thereof and passing through a reversing conveying path 305 and a discharging conveying path 304.

[0023] When forming images on both sides of the sheet S, the sheet S on which the image on the first side has been formed is switched back and conveyed in a duplex reversing unit 306, and the leading and trailing ends of the sheet S are swapped and conveyed upside down to a duplex conveying path 307. Thereafter, the sheet S is rejoined by the registration rollers 213 in time with the subsequent sheet S fed from a storage unit 212 for the sheet S inside the image forming unit 102 or from any of the aforementioned externally connected sheet feeding devices, and an image is formed on the second side in the same process as on the first side, and the sheet is discharged via a discharge conveying path 304.

[0024] The image forming apparatus main body 101 of this embodiment can form full-color images using all of the Y, M, C, and K image forming stations 200Y, 200M, 200C, and 200K described above, as well as black-and-white images using only the K image forming station 200K.

[0025] During black-and-white image formation, a separation mechanism (not shown) displaces the primary transfer rollers 207Y, 207M, and 207C, the primary transfer auxiliary roller 218, and the intermediate transfer belt 208 to the positions indicated by the dashed lines in FIG. 2. This mechanism allows the Y, M, and C image forming stations 200Y, 200M, and 200C, which are separated from the intermediate transfer belt 208, to stop rotating. This means that unnecessary wear on parts due to unnecessary rotation can be prevented in the Y, M, and C image forming stations 200Y, 200M, and 200C, thereby extending their lifespans.

[0026] Meanwhile, the K photosensitive drum 201K has a larger diameter suitable for a longer life than the Y, M, and C photosensitive drums 201Y, 201M, and 201C. The K primary charger 202K is a non-contact type using a corona charger suitable for a longer life than the contact type using a roller charger of the Y, M, and C primary chargers 202Y, 202M, and 202C. Furthermore, the K toner bottle 205K has a larger capacity suitable for a longer life than the Y, M, and C toner bottles 205Y, 205M, and 205C.

[0027] With the above configuration, even for users who frequently use black-and-white image formation, it is possible to prevent the maintenance interval for the frequently used K image forming station 200K from becoming shorter than that for the less frequently used Y, M, and C image forming stations 200Y, 200M, and 200C. Furthermore, since the large-diameter drum configuration using a corona charger has a wider charging width and is more suitable for high speeds than the small-diameter drum configuration using a roller charger, it is also possible to improve productivity during black-and-white image formation.

[0028] In the image forming unit 102, in which the image forming stations 200Y to 200K have different conditions, differences in the toner charge amount on the photosensitive drums 201Y to 201K may occur due to differences in shape and wear. If differences in the toner charge amount occur, the toner image may not be transferred uniformly to the sheet S in the secondary transfer process, resulting in a defective image. Therefore, the K photosensitive drum 201K is provided with a pre-transfer charger 220 consisting of a corona charger to equalize the toner charge amount with the Y, M, and C photosensitive drums 201Y, 201M, and 201C.

[0029] As described above, the configuration of this embodiment makes it possible to provide an image forming apparatus main body 101 that is excellent in terms of high productivity, high image quality, high stability, and long life, not only in full-color image formation but also in black-and-white image formation.

[0030] [Pre-fixing transport section] Next, the detailed configuration of the pre-fixing conveyance section 410 and its surroundings will be described with reference to FIG. 5. FIG. 5 is a cross-sectional view showing the secondary transfer section, the pre-fixing conveyance section 410, and the fixing section 50. In recent years, there has been a demand for devices that achieve high image quality, high productivity, and high image position accuracy. To achieve high image quality, it is important to maintain a consistent sheet posture after transfer and before fixing. It is also important to stably supply an appropriate amount of heat to the sheet to maintain uniform gloss and other properties. Furthermore, to achieve high image position accuracy, it is important to feed the sheet without skewing, turning, or skew. However, for example, in a compact image forming apparatus where the distance between the transfer section and the fixing section is short, the sheet is nipped and conveyed simultaneously in the transfer section and the fixing section.

[0031] On the other hand, because the transfer unit transfers the toner image to the sheet, it is difficult to fine-tune the sheet conveyance speed. Furthermore, the outer diameter of the roller in the fixing unit expands due to heat, making it difficult to maintain a constant sheet conveyance speed. Therefore, when a sheet is conveyed simultaneously through the transfer unit and fixing unit, problems arise, such as poor image quality due to mutual pulling and pushing, and sheet conveyance rotation, i.e., slanted images. For this reason, in this embodiment, a pre-fixing conveyance unit 410 is provided between the secondary transfer unit and the fixing unit 50, increasing the distance from the secondary transfer unit to the fixing unit 50 and avoiding the above-mentioned problems.

[0032] In the sheet conveyance direction FD, a transfer guide 219 is provided between the pre-fixing conveyance section 410 and the secondary transfer nip section N1 to guide the sheet conveyed from the secondary transfer nip section N1 toward the pre-fixing conveyance section 410. In addition, in the sheet conveyance direction FD, a fixing entrance guide 53 is provided between the pre-fixing conveyance section 410 and the fixing nip section N2 to guide the sheet conveyed by the pre-fixing conveyance section 410 to the fixing nip section N2.

[0033] As shown in FIG. 5, the pre-fixing conveyance section 410 is positioned lower than the secondary transfer nip N1 and the fixing nip N2. With this configuration, the leading edge of the sheet that has passed through the secondary transfer nip N1 is conveyed along the transfer guide 219 toward the pre-fixing conveyance section 410. The pre-fixing conveyance section 410 conveys the sheet along the sheet conveyance surface 410a toward the fixing section 50. The fixing entrance guide 53 has a guide surface 53a that guides the leading edge of the sheet conveyed along the sheet conveyance surface 410a toward the fixing nip N2. The guide surface of the fixing entrance guide 53 is downstream of the pre-fixing conveyance section 410 in the sheet conveyance direction FD and intersects with the imaginary line 410a' of the sheet conveyance surface 410a upstream of the fixing nip N2. With this configuration, the leading edge of the sheet being conveyed from the pre-fixing conveyance section 410 to the fixing section 50 abuts against the fixing entrance guide 53, and the sheet follows the fixing entrance guide 53, so that the sheet is properly introduced into the fixing nip section N2. In other words, it is possible to avoid image defects that occur when unfixed toner on the sheet comes into contact with the heating roller 51, and conveyance defects such as wrinkles and bent corners.

[0034] The pre-fixing conveyance section 410 includes a conveyance belt 411 and a drive roller 412 and driven rollers 412a, 412b, and 412c as tension members that rotatably tension the conveyance belt 411. The pre-fixing conveyance section 410 also includes a drive motor 413 as a drive means that rotates the drive roller 412 to rotate the conveyance belt 411. The conveyance belt 411 is an endless belt formed with a number of holes, and is a breathable member that allows air to pass between the inside and outside of the circumferential surface of the conveyance belt 411 through the holes. A suction fan 414 is disposed on the inside of the circumferential surface of the conveyance belt 411 as an air suction unit that attracts the sheet to the circumferential surface of the conveyance belt 411. The suction fan 414 is capable of sucking air from the outside to the inside of the circumferential surface of the conveyance belt 411 through the many holes formed in the conveyance belt 411, thereby applying suction force to the circumferential surface of the conveyance belt 411 to convey the sheet. As a result, the pre-fixing conveyance section 410 adsorbs the sheet onto the conveyance belt 411 (on the belt) by the suction fan 414, and conveys the sheet by rotating the conveyance belt 411 by the drive motor 413.

[0035] Here, if a configuration in which the pre-fixing conveyance unit 410 is provided between the secondary transfer unit and the fixing unit 50 is arranged in a single housing, the device becomes larger and the workability of carrying in and installing the device decreases. For this reason, in this embodiment, the secondary transfer unit and the pre-fixing conveyance unit 410 are supported on a first housing 102a that is the housing of the image forming unit 102, and the fixing unit 50 is supported on a second housing 103a that is the housing of the fixing conveyance unit 103. Then, when installing the device, the image forming device main body 101 is configured by connecting the image forming unit 102 to the fixing conveyance unit 103. In other words, dividing the image forming device main body 101 into multiple module devices improves the workability of carrying in and installing the device.

[0036] As described in Fig. 2, the first housing 102a is provided with components for transferring a toner image to a sheet S, such as the image forming stations 200Y, 200M, 200C, and 200K, the intermediate transfer belt 208, the sheet S storage section 212, and the pre-fixing conveyance section 410, before the toner image is fixed to the sheet. The second housing 103a is provided with components for fixing a toner image to a sheet, such as the fixing section 50, the cooler 302, and the discharge conveyance path 304, before the sheet is discharged, as described in Fig. 4. By connecting the first housing 102a to the second housing 103a, the sheet can be conveyed from the pre-fixing conveyance section 410 supported by the first housing 102a to the fixing section 50 supported by the second housing 103a.

[0037] In this configuration in which the image forming apparatus main body 101 is divided into multiple module devices, there are many parts between the pre-fixing conveyance section 410 supported by the first housing 102a and the fixing entrance guide 53 of the fixing section 50 supported by the second housing 103a, resulting in large dimensional tolerances. That is, the tolerances of the support structure of the pre-fixing conveyance section 410 relative to the first housing 102a, the connection structure between the first housing 102a and the second housing 103a, and the support structure of the fixing section 50 relative to the second housing 103a all exist between the pre-fixing conveyance section 410 and the fixing entrance guide 53 of the fixing section 50.

[0038] The accumulation of these many tolerances can lead to the following sheet transport problems and image defects: For example, if the pre-fixing conveyance section 410 is too low in height relative to the fixing inlet guide 53, the leading edge of the sheet will slip between the fixing inlet guide 53 and the pre-fixing conveyance section 410 without contacting the fixing inlet guide 53, causing the sheet to jam. Conversely, if the pre-fixing conveyance section 410 is too high in height relative to the fixing inlet guide 53, the leading edge of the sheet will not contact the fixing inlet guide 53 but will be introduced into the fixing nip N2, causing image defects such as unfixed toner on the sheet coming into contact with the heating roller 51, or transport problems such as wrinkles or bent corners.

[0039] Therefore, in this embodiment, the pre-fixing conveyance section 410 is supported swingably on the first housing 102a, and a part of the pre-fixing conveyance section 410 is brought into contact with a positioning member 131a provided on the second housing 103a, thereby positioning the pre-fixing conveyance section 410. This configuration will be described below with reference to FIGS.

[0040] [Positioning structure of pre-fixing transport section] 5 to 7, a configuration for appropriately positioning the swinging pre-fixing conveyance section 410 when connecting the image forming section 102 and the fixing conveyance section 103 will be described. FIG. 6 is a cross-sectional view of the first housing 102a of the image forming section 102, the positioning section 131 fixed to the fixing conveyance section 103, and the pre-fixing conveyance section 410, viewed from the bottom of the image forming apparatus main body 101 in an upward direction. FIG. 7 is a view of the positioning section 131 having the positioning member 131a, viewed from the conveyance direction. The second housing 103a that supports the fixing section 50 is connected to the first housing 102a so that a portion of the pre-fixing conveyance section 410 enters the interior, thereby allowing the sheet to be transported from the pre-fixing conveyance section 410 to the fixing section 50.

[0041] The pre-fixing conveyance section 410 is supported by a swing support section 415 so as to be swingable relative to the first housing 102a about a swing axis α (the central axis of the first swing support member 415a and the second swing support member 415b) along the sheet width direction (the up-down direction in FIG. 6) that intersects (orthogonal in this embodiment) the sheet conveyance direction FD. The swing support section 415 has a first swing support member 415a as a first support member and a second swing support member 415b as a second support member that swingably support the pre-fixing conveyance section 410 on both sides of the pre-fixing conveyance section 410 in the sheet width direction. The central axes of the first swing support member 415a and the second swing support member 415b exist on the same straight line parallel to the sheet width direction. Furthermore, the pre-fixing transport section 410 has a contact section 416, at least a part of which enters the second housing 103a when the first housing 102a and the second housing 103a are connected to each other.

[0042] Meanwhile, a positioning member 131a is provided in the second housing 103a. The positioning member 131a abuts against a contact portion 416 provided on a part of the pre-fixing conveyance section 410, thereby positioning the pre-fixing conveyance section 410 in the swing direction about the swing axis α. In this embodiment, the positioning member 131a is provided below the pre-fixing conveyance section 410 and supports a part of the pre-fixing conveyance section 410 by abutting against the contact portion 416 from below. As a result, the pre-fixing conveyance section 410 is supported at a total of three points: two swing support points provided by the first swing support member 415a and the second swing support member 415b, and one support point provided by the abutment between the contact portion 416 and the positioning member 131a.

[0043] In addition, the pre-fixing conveying section 410 may be positioned by biasing it with a spring or the like so that the downstream side of the sheet conveying direction FD faces upward around the swing axis α, and this upward swing is regulated by a positioning member.

[0044] The positioning configuration of the pre-fixing conveyance section 410 of this embodiment will be described in more detail. The pre-fixing conveyance section 410 is provided with a first swing support member 415a and a second swing support member 415b on the upstream side in the sheet conveyance direction FD and on the front and rear sides in the sheet width direction perpendicular to the sheet conveyance direction FD. The front and rear sides in the sheet width direction correspond to the front and rear sides of the image forming apparatus main body 101, respectively. The front side of the image forming apparatus main body 101 is the side operated by the user, and for example, an operation panel for operating the image forming apparatus 100 is disposed thereon. Similarly, the rear side is the rear side of the image forming apparatus main body 101.

[0045] The first swing support member 415a and the second swing support member 415b are swingably supported relative to the first housing 102a. In this embodiment, the first swing support member 415a and the second swing support member 415b are shaft-shaped, and are swingably supported by hole-shaped members provided in the first housing 102a. However, the swing support configuration of the pre-fixing transport section 410 is not limited to this, and it is also possible to provide holes in the pre-fixing transport section 410 and have the shaft-shaped first swing support member 415a and second swing support member 415b protrude from the first housing 102a.

[0046] The pre-fixing conveyance section 410 also includes a contact portion (oscillation restricting member) 416 located downstream in the sheet conveyance direction FD and approximately at the center of the pre-fixing conveyance section 410 in the sheet width direction. The contact portion 416 restricts the oscillation of the pre-fixing conveyance section 410 by contacting the positioning member 131a as described above. In this manner, the pre-fixing conveyance section 410 is supported at three points: two oscillation support members 415a and 415b and one contact portion (oscillation restricting member) 416. This three-point support structure is effective in suppressing twisting within the pre-fixing conveyance section 410 unit and making it less likely for the conveyance belt 411 of the pre-fixing conveyance section 410 to shift. From the perspective of belt shifting, it is desirable to have a single contact portion 416, but this arrangement is not limiting and multiple contact portions 416 may be arranged in the sheet width direction.

[0047] As shown in FIG. 5, the positioning member 131a is attached to a fixing conveyance unit support 132 provided on the surface of the second housing 103a that mates with the first housing 102a, in the same phase as the abutment portion 416 in the sheet width direction. As shown in FIG. 7, the positioning unit 131 includes the positioning member 131a, a shaft 131b that rotatably supports the positioning member 131a, and a support member 131c that supports the shaft 131b. The shaft 131b is a rotation shaft disposed along the sheet width direction, and the positioning member 131a is a roller that can rotate around this rotation shaft. Note that the positioning member 131a may be a rotatable roller, or may be, for example, a cylindrical or semi-cylindrical member with a smooth, slippery surface, as long as it is configured to reduce sliding resistance with the abutment portion 416 of the pre-fixing conveyance unit 410 when connecting the first housing 102a and the second housing 103a, as described below.

[0048] Such positioning member 131a is provided so that its position in the up-down direction (height direction) can be adjusted relative to second housing 103a. Specifically, support member 131c is provided with an adjustment margin so that the position of positioning member 131a can be adjusted in the height direction. That is, support member 131c is attached to fixing conveyance unit support 132 by bolt 131e via elongated hole 131d that is long in the up-down direction. Therefore, by changing the fixing position of bolt 131e relative to elongated hole 131d, the height direction position of positioning member 131a supported by support member 131c via shaft 131b can be adjusted.

[0049] This allows the positioning member 131a to be assembled to the second housing 103a with its height position adjusted so that the pre-fixing conveyance section 410 has a constant height relationship with the fixing entrance guide 53. This also makes it possible to suppress variations in the dimensional tolerance in the height direction from the contact portion 416 to the fixing entrance guide 53. Here, the angle and width of the guide surface 53a are set so that the leading edge of the sheet will contact the guide surface 53a of the fixing entrance guide 53 even if there is variation in the angle of the sheet conveyance surface 410a due to variations in the tolerance in the height direction from the contact portion 416 to the sheet conveyance surface 410a or variation in the sheet posture due to curling of the leading edge of the sheet.

[0050] Next, the positioning behavior of the pre-fixing conveyance section 410 when the first housing 102a and the second housing 103a are brought close to each other and connected will be described with reference to FIG. 8. FIG. 8 shows a cross-sectional view of the pre-fixing conveyance section 410 in a state in which its swinging due to its own weight is restricted by the swing restricting section 221. That is, the pre-fixing conveyance section 410 has the swing restricting section 221 that can restrict the swing range about the swing axis α when the first housing 102a is not connected to the second housing 103a. The swing range restricted by the swing restricting section 221 is set so that the positioning member 131a can abut against the abutment section 416 when the first housing 102a is connected to the second housing 103a.

[0051] Specifically, the swing restriction section 221 has a restriction plate section 222 and a stepped screw 223 as a restriction shaft section. The restriction plate section 222 is fixed to the first housing 102a so as to support the weight of the pre-fixing conveyance section 410 and restrict the swing range of the pre-fixing conveyance section 410. A through hole 222a is formed in the restriction plate section 222, and a first swing support member 415a and a second swing support member 415b are inserted into the through hole 222a. As a result, the pre-fixing conveyance section 410 is supported swingably with respect to the restriction plate section 222.

[0052] The regulating plate 222 has an engagement hole 222b formed along an arc centered on the oscillation axis α. A frame supporting the tension roller of the pre-fixing conveyance section 410 has a screw hole formed therein, and with the first oscillation support member 415a and the second oscillation support member 415b inserted into the through-hole 222a of the regulating plate 222, the shoulder screw 223 is passed through the engagement hole 222b and fastened to the screw hole of the pre-fixing conveyance section 410 together with the regulating plate 222. This allows the shoulder screw 223 to oscillate within the engagement hole 222b along an arc centered on the oscillation axis α, and the pre-fixing conveyance section 410 can oscillate within the engagement range of the shoulder screw 223 and the engagement hole 222b. When the image forming unit 102 is viewed alone, the pre-fixing conveying unit 410 can swing within the range regulated by the swing regulating unit 221 (i.e., the engagement range between the shoulder screw 223 and the engagement hole 222b), and the swing is regulated by the swing regulating unit 221 due to its own weight.

[0053] In this embodiment, the swing range is regulated by a stepped screw, but the swing regulation configuration is not limited to this, and a member that can regulate the swing range may be provided on the pre-fixing conveying section 410 or the first housing 102a as long as it can regulate the swing range of the pre-fixing conveying section 410.

[0054] On the other hand, the contact portion 416 has a positioning surface 416a and a guide surface 416b. The positioning surface 416a contacts the positioning member 131a to position the pre-fixing conveyance portion 410. The guide surface 416b is provided downstream of the positioning surface 416a in the sheet conveyance direction FD, and guides the positioning member 131a to the positioning surface 416a when connecting the first housing 102a to the second housing 103a. The contact portion 416 has a substantially trapezoidal shape when viewed from the sheet width direction, and is made of a material with good sliding properties. The guide surface 416b is formed so as to slope upward as it moves downstream in the sheet conveyance direction FD.

[0055] The upper swing restriction position of swing restriction portion 221 is such that, when first housing 102a and second housing 103a are connected, the outer peripheral surface of positioning member 131a abuts against guide surface 416b of abutment portion 416. That is, when first housing 102a and second housing 103a are connected in a state in which swinging of pre-fixing conveyance portion 410 due to its own weight is restricted, in other words, in a state in which shoulder screw 223 is engaged with the upper edge of engagement hole 222b, the swing range of pre-fixing conveyance portion 410 is restricted so that guide surface 416b abuts against positioning member 131a.

[0056] In this embodiment, with this configuration, when the first housing 102a and the second housing 103a are connected, the abutment portion 416 of the pre-fixing conveyance section 410 that has entered the second housing 103a first abuts the guide surface 416b against the positioning member 131a. Then, as the pre-fixing conveyance section 410 further enters the second housing 103a, the guide surface 416b slides against the positioning member 131a, and the pre-fixing conveyance section 410 is pushed upward. Then, with the first housing 102a and the second housing 103a connected, the positioning member 131a is positioned on the positioning surface 416a, and the pre-fixing conveyance section 410 is positioned in the swing direction. At this time, the guide surface 416b and the positioning surface 416a smoothly abut against the positioning member 131a.

[0057] Furthermore, when first housing 102a and second housing 103a are joined, they may be misaligned in the front-rear direction when they are joined together. To allow the outer peripheral surface of positioning member 131a to abut against guide surface 416b of abutting portion 416 within the range of this expected amount of misalignment, a certain width is provided in a front-rear direction for abutting portion 416.

[0058] With the above configuration, when the first housing 102a and the second housing 103a are connected, the pre-fixing conveyance section 410 swings smoothly, and the height of the fixing section 50 relative to the fixing entrance guide 53 is appropriately determined. That is, when the first housing 102a and the second housing 103a are connected, the abutment section 416 rides up onto the positioning member 131a, restricting the swinging of the pre-fixing conveyance section 410. Then, the guide surface 53a of the fixing entrance guide 53 and the imaginary line 410a' of the sheet conveyance surface 410a of the pre-fixing conveyance section 410 intersect at an appropriate point.

[0059] In this embodiment, the pre-fixing conveyance section 410 is positioned relative to the fixing section 50 by abutment between the positioning member 131a provided on the second housing 103a and the abutment section 416 provided on the pre-fixing conveyance section 410. This reduces the number of members required for positioning between the pre-fixing conveyance section 410 and the fixing section, thereby reducing the tolerance for positioning. As a result, in a configuration in which the pre-fixing conveyance section 410 and the fixing section 50 are supported on separate housings and these housings are connected, it is possible to prevent sheet conveyance problems and image defects from occurring.

[0060] Therefore, in this embodiment, even for large devices, it is possible to pack and transport the device in a state where it is separated into multiple modules, improving workability during logistics up to installation, while suppressing image defects caused by unfixed toner on the sheet coming into contact with the heating roller 51, as well as transport defects such as wrinkles and bent corners, thereby improving image quality.

[0061] <Second embodiment> The second embodiment will be described with reference to Figures 9 and 10. In the first embodiment described above, the case where there is one pre-fixing conveying section 410 has been described. In contrast to this, in this embodiment, multiple pre-fixing conveying sections are arranged between the secondary transfer section and the fixing section 50. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals have been used to designate similar configurations, and explanations and illustrations thereof will be omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0062] First, when a sheet jam occurs near the pre-fixing conveyance unit, in order to improve jam clearance, it is desirable to clear the jam with the pre-fixing conveyance unit and its surrounding units pulled out. However, when a configuration is adopted in which a portion of the pre-fixing conveyance unit 410 in the first housing 102a is positioned by abutting against the positioning member 131a in the second housing 103a, as in the first embodiment, the pre-fixing conveyance unit 410 is disposed across the first housing 102a and the second housing 103a. In this case, the pre-fixing conveyance unit 410 is hidden by the support pillars of the frame of the first housing 102a, and the pre-fixing conveyance unit 410 cannot be pulled out.

[0063] Furthermore, as described in the first embodiment, the posture of the sheet entering the fixing unit 50 is also important for improving image quality, and therefore a highly accurate relative positional relationship is required between the fixing unit 50 and the upstream pre-fixing conveyance unit 410. In other words, if it is necessary to pull out the unit to improve jam clearance, and a highly accurate relative positional relationship is required between the fixing unit 50 and the upstream pre-fixing conveyance unit 410, it is desirable to configure the pre-fixing conveyance unit as being divided into two or more conveyance units.

[0064] Therefore, in this embodiment, in addition to a first pre-fixing conveyance section 430 as a first conveyance section corresponding to the pre-fixing conveyance section 410 of the first embodiment, a second pre-fixing conveyance section 420 as a second conveyance section is provided. Fig. 9 is a schematic cross-sectional view of an image forming apparatus (image forming system) 100A having an image forming apparatus main body 101A of this embodiment. Fig. 10 is a cross-sectional view showing the secondary transfer section, the first pre-fixing conveyance section 430, the second pre-fixing conveyance section 420, and the fixing section 50.

[0065] In the sheet transport direction FD, between the secondary transfer unit and the fixing unit 50, there are disposed a second pre-fixing conveyance unit 420 disposed upstream in the sheet transport direction FD and a first pre-fixing conveyance unit 430 disposed downstream. That is, the second pre-fixing conveyance unit 420 is disposed between the first pre-fixing conveyance unit 430 and the secondary transfer unit in the sheet transport direction FD, and conveys a sheet onto which a toner image has been transferred at the secondary transfer unit toward the first pre-fixing conveyance unit 430. The second pre-fixing conveyance unit 420 is supported by the first housing 102a so that it can be inserted into and removed from the first housing 102a for jam clearance. The second pre-fixing conveyance unit 420 is pulled out from the first housing 102a from the front side by, for example, opening a front door of the image forming unit 102, and is pushed to the rear side when stored in the first housing 102a.

[0066] Similar to the pre-fixing conveyance section 410 described in the first embodiment, the first pre-fixing conveyance section 430 is supported to be swingable relative to the first housing 102a and is positioned in the swing direction by a positioning member 131a. That is, the support and positioning configurations of the first pre-fixing conveyance section 430 are the same as those of the pre-fixing conveyance section 410 of the first embodiment. Specifically, the first pre-fixing conveyance section 430 is supported by a swing support section 435 to be swingable relative to the first housing 102a about a swing axis α along the sheet width direction that intersects (orthogonal in this embodiment) the sheet conveyance direction FD. The configuration of the swing support section 435 is the same as that of the swing support section 415 of the first embodiment. The first pre-fixing conveyance section 430 also has an abutment section 436, at least a portion of which enters the second housing 103a when the first housing 103a and the second housing 103a are connected to each other. The configuration of the contact portion 436 is similar to that of the contact portion 416 of the first embodiment.

[0067] On the other hand, a positioning member 131a is provided in the second housing 103a. The positioning member 131a abuts against a contact portion 436 provided on a part of the first pre-fixing conveyance section 430, thereby positioning the first pre-fixing conveyance section 430 in the swing direction about the swing axis α. The positioning member 131a has the same configuration as in the first embodiment, and is attached to a fixing conveyance section support 132 provided on the surface of the second housing 103a that joins with the first housing 102a, in the same phase as the abutment portion 436 in the sheet width direction.

[0068] In the sheet conveyance direction FD, a transfer guide 219 is provided between the second pre-fixing conveyance section 420 and the secondary transfer nip N1 to guide the sheet conveyed from the secondary transfer nip N1 toward the second pre-fixing conveyance section 420. In addition, in the sheet conveyance direction FD, a fixing entrance guide 53 is provided between the first pre-fixing conveyance section 430 and the fixing nip N2 to guide the sheet conveyed by the first pre-fixing conveyance section 430 toward the fixing nip N2. As shown in FIG. 10 , the upstream end of the second pre-fixing conveyance section 420 is positioned lower than the secondary transfer nip N1 when viewed in the sheet width direction perpendicular to the sheet conveyance direction FD. With this configuration, the leading edge of the sheet that has passed through the secondary transfer nip N1 is conveyed along the transfer guide 219 toward the second pre-fixing conveyance section 420.

[0069] The upstream end of the first pre-fixing conveyance section 430 is disposed at a position lower than the downstream end of the second pre-fixing conveyance section 420 in order to receive the sheet from the second pre-fixing conveyance section 420. With this configuration, the leading edge of the sheet that has passed through the second pre-fixing conveyance section 420 is conveyed toward the first pre-fixing conveyance section 430.

[0070] The first pre-fixing conveyance section 430 conveys a sheet toward the fixing section 50 along the sheet conveyance surface 430a. The fixing entrance guide 53 has a guide surface 53a that guides the leading edge of the sheet conveyed along the sheet conveyance surface 430a toward the fixing nip N2. The guide surface of the fixing entrance guide 53 is downstream of the first pre-fixing conveyance section 430 in the sheet conveyance direction FD and intersects with the imaginary line 430a' of the sheet conveyance surface 430a upstream of the fixing nip N2. With this configuration, the leading edge of the sheet conveyed from the first pre-fixing conveyance section 430 to the fixing section 50 abuts against the fixing entrance guide 53, and the sheet's posture conforms to the fixing entrance guide 53, so that the sheet is properly introduced into the fixing nip N2. In other words, this can prevent image defects caused by unfixed toner on the sheet coming into contact with the heating roller 51, as well as conveyance defects such as wrinkles and bent corners.

[0071] The second pre-fixing conveyance section 420 includes a conveyance belt 421 and a drive roller 422 and driven rollers 422a, 422b, and 422c as tension members that rotatably tension the conveyance belt 421. The second pre-fixing conveyance section 420 also includes a drive motor 423 that rotates the drive roller 422 to rotate the conveyance belt 421. The conveyance belt 421 is an endless belt formed with a number of holes, and is a breathable member that allows air to pass between the inside and outside of the circumferential surface of the conveyance belt 421 through the holes. A suction fan 424 is disposed on the inside of the circumferential surface of the conveyance belt 421 as an air suction unit that attracts the sheet to the circumferential surface of the conveyance belt 421. The suction fan 424 can apply suction force to the circumferential surface of the conveyance belt 421 to transport the sheet by sucking air from the outside to the inside of the circumferential surface of the conveyance belt 421 through the many holes formed in the conveyance belt 421. As a result, the second pre-fixing conveyance section 420 adsorbs the sheet onto the conveyance belt 421 by the suction fan 424, and conveys the sheet by rotating the conveyance belt 421 by the drive motor 423.

[0072] The components of the first pre-fixing conveyance section 430 are the same as those of the pre-fixing conveyance section 410 described in the first embodiment. That is, the first pre-fixing conveyance section 430 includes a conveyance belt 431, and a drive roller 432 and driven rollers 432a, 432b, and 432c as tension members that rotatably tension the conveyance belt 431. The first pre-fixing conveyance section 430 also includes a drive motor 433 that rotates the drive roller 432 to rotate the conveyance belt 431. A suction fan 434 is disposed inside the circumferential surface of the conveyance belt 431 as an air suction unit that attracts the sheet to the circumferential surface of the conveyance belt 431. The components of the fixing conveyance section 103 and the fixing section 50 are also the same as those described in the first embodiment.

[0073] With the above configuration, in this embodiment, in addition to the effects described in the first embodiment, jam recovery performance can be improved. Note that, although the configuration in which two pre-fixing conveyance units are provided has been described in this embodiment, a configuration in which three or more pre-fixing conveyance units are provided may also be used. In this case, the pre-fixing conveyance unit disposed most downstream in the sheet transport direction FD between the secondary transfer unit and the fixing unit 50 has the same support and positioning configuration as the pre-fixing conveyance unit 410 in the first embodiment.

[0074] <Third embodiment> The third embodiment will be described with reference to Figures 11 and 12. In the first and second embodiments described above, a configuration in which the image forming unit 102 is directly connected to the fixing and conveying unit 103 has been described. In contrast, in this embodiment, the image forming unit 102 and the fixing and conveying unit 103 are connected via an intermediate conveying unit 108. Since the other configurations and functions are the same as those of the second embodiment described above, the same reference numerals are used for the similar configurations, and explanations and illustrations thereof will be omitted or simplified. The following description will focus on the points that are different from the second embodiment.

[0075] A distance of approximately 19.2 inches (487.7 mm) between the secondary transfer nip N1 and the fixing nip N2, commonly referred to as a standard size, is desirable for high image quality and high productivity. For this reason, in the second embodiment described above, the distance L1 between the secondary transfer nip N12 and the fixing nip N2 is set to approximately 500 mm, which is greater than 19 inches (483 mm). Therefore, even with the configuration of the second embodiment, if the length of a sheet in the conveying direction FD is 19 inches or less, the sheet is conveyed without being sandwiched between both the secondary transfer nip N1 and the fixing nip N2. In other words, for a sheet length of 19 inches, the secondary transfer nip N1 and the fixing nip N2 do not nip the sheet simultaneously, preventing image defects and providing a high-image-quality, high-precision product.

[0076] However, in recent years, there has been a growing demand for electrophotographic image forming apparatuses that can form images on not only standard-sized sheets but also so-called long sheets, which are sheets longer in the conveying direction than standard-sized sheets. Meanwhile, in the case of a sheet longer than 19 inches, generally referred to as a long sheet, the configuration of the second embodiment causes the secondary transfer nip N1 and the fixing nip N2 to simultaneously nip the sheet. Furthermore, if the sheet speed at the fixing nip N2 (fixing conveying speed VF) is faster than the sheet conveying speed at the secondary transfer nip N1 (transfer conveying speed VT), the fixing unit 50 will pull the sheet.

[0077] The clamping force of the fixing unit 50 on the sheet is designed to be greater than the clamping force of the secondary transfer unit on the sheet in order to fix the toner on the sheet. Therefore, the sheet passing through the secondary transfer unit is pulled by the fixing unit 50, which may cause transfer failure of the toner image carried on the intermediate transfer belt 208.

[0078] Furthermore, the image quality may be degraded when the unfixed toner on the sheet comes into contact with the heating roller 51 upstream of the fixing nip portion N2 in the conveying direction.

[0079] On the other hand, if the transfer conveying speed VT is faster than the fixing conveying speed VF, the leading edge of the sheet may hit the fixing nip portion N2, causing the sheet to be pushed back, which may result in poor transfer of the toner image carried on the intermediate transfer belt 208.

[0080] In contrast, if the distance L1 between the secondary transfer nip portion N1 and the fixing nip portion N2 is set to about 800 mm, which is generally more than 30 inches (762 mm), which is often used for long sheets, the image defects described above can be avoided. However, if the distance L1 is increased in this way, the image forming unit 102 or fixing conveyance unit 103 that constitutes the image forming apparatus main body 101 becomes a large device, and it takes time to carry in and install the device.

[0081] Therefore, in this embodiment, an intermediate conveying unit 108, which is a separate module from the image forming unit 102 and the fixing and conveying unit 103, is disposed between them to increase the distance L1 between the secondary transfer nip N1 and the fixing nip N2. That is, in this embodiment, the image forming apparatus main body 101B is configured from three separate modules: the image forming unit 102, the intermediate conveying unit 108, and the fixing and conveying unit 103. In this embodiment, the housing 108a of the intermediate conveying unit 108 corresponds to the first housing, the housing 103b of the fixing and conveying unit 103 corresponds to the second housing, and the housing 102b of the image forming unit 102 corresponds to the third housing.

[0082] Furthermore, in this embodiment, in addition to a first pre-fixing conveyance section 460 as a first conveyance section corresponding to the pre-fixing conveyance section 410 of the first embodiment, a third pre-fixing conveyance section 450 as a third conveyance section, and a second pre-fixing conveyance section 440 as a second conveyance section corresponding to the second pre-fixing conveyance section 420 of the second embodiment are provided. That is, the second pre-fixing conveyance section 440, the third pre-fixing conveyance section 450, and the first pre-fixing conveyance section 460 are arranged from the upstream side in the sheet conveyance direction.

[0083] The configuration of this embodiment will be described with reference to Figures 11 and 12. Figure 11 is a schematic cross-sectional view of an image forming apparatus (image forming system) 100B having an image forming apparatus main body 101B of this embodiment. Figure 12 is a cross-sectional view showing the secondary transfer unit, second pre-fixing conveyance unit 440, third pre-fixing conveyance unit 450, first pre-fixing conveyance unit 460, and fixing unit 50.

[0084] In the sheet conveyance direction FD, between the secondary transfer unit and the fixing unit 50, there are arranged a second pre-fixing conveyance unit 440 arranged on the most upstream side in the sheet conveyance direction FD, a first pre-fixing conveyance unit 460 arranged on the most downstream side, and a third pre-fixing conveyance unit 450 between the second pre-fixing conveyance unit 440 and the first pre-fixing conveyance unit 460. Similar to the second pre-fixing conveyance unit 420 described in the second embodiment, the second pre-fixing conveyance unit 440 is supported by the housing 102b as the third housing so that it can be pulled out for jam clearance.

[0085] The third pre-fixing conveyance section 450 is fixedly supported by the housing 102b. That is, the housing 102b supports the secondary transfer section, the second pre-fixing conveyance section 440, and the third pre-fixing conveyance section 450. The housing 102b is disposed upstream of the housing 108a in the sheet conveyance direction FD, and is connected to the housing 108a so that a portion of the third pre-fixing conveyance section 450 enters the interior of the housing 108a, thereby allowing the sheet to be conveyed from the third pre-fixing conveyance section 450 to the first pre-fixing conveyance section 460. Note that, similar to the pre-fixing conveyance section 410 described in the first embodiment, the third pre-fixing conveyance section 450 may be supported swingably by the housing 102b, and the swing direction may be positioned by a positioning member provided on the housing 108a of the intermediate conveyance section 108.

[0086] When viewed in the width direction of the sheet, which is perpendicular to the sheet conveying direction FD, the upstream end of the first pre-fixing conveying section 460 is disposed at a position lower than the downstream end of the third pre-fixing conveying section 450 in order to receive the sheet from the third pre-fixing conveying section 450. With this configuration, the leading edge of the sheet that has passed through the third pre-fixing conveying section 450 is conveyed toward the first pre-fixing conveying section 460.

[0087] The first pre-fixing conveyance section 460 conveys a sheet toward the fixing section 50 along the sheet conveyance surface 460a. The fixing entrance guide 53 has a guide surface 53a that guides the leading edge of the sheet conveyed along the sheet conveyance surface 460a toward the fixing nip N2. The guide surface 53a of the fixing entrance guide 53 is downstream of the first pre-fixing conveyance section 460 in the sheet conveyance direction FD and intersects with the imaginary line 460a' of the sheet conveyance surface 460a upstream of the fixing nip N2. With this configuration, the leading edge of the sheet conveyed from the first pre-fixing conveyance section 460 to the fixing section 50 abuts against the fixing entrance guide 53, and the sheet's posture conforms to the fixing entrance guide 53, so that the sheet is properly introduced into the fixing nip N2. In other words, it is possible to avoid image defects caused by unfixed toner on the sheet coming into contact with the heating roller 51, as well as conveyance defects such as wrinkles and bent corners.

[0088] The components provided in the second pre-fixing conveying section 440 and the third pre-fixing conveying section 450 are the same as those in the second pre-fixing conveying section 420 described in the second embodiment. Moreover, the components provided in the first pre-fixing conveying section 460 are the same as those in the pre-fixing conveying section 410 described in the first embodiment.

[0089] That is, the second pre-fixing conveying section 440, the third pre-fixing conveying section 450, and the first pre-fixing conveying section 460 respectively include conveying belts 441, 451, and 461, and driving rollers 442, 452, and 462 and driven rollers 442a, 452a, 462a, 442b, 452b, 462b, 442c, 452c, and 462c as tensioning members that rotatably tension the conveying belts 441, 451, and 461. The second pre-fixing conveying section 440, the third pre-fixing conveying section 450, and the first pre-fixing conveying section 460 also include driving motors 443, 453, and 463 that rotate the driving rollers 442, 452, and 462, respectively, to rotate the conveying belts 441, 451, and 461. Suction fans 444, 454, and 464 are arranged inside the circumferential surfaces of the conveyor belts 441, 451, and 461 as air suction units that suck the sheets onto the circumferential surfaces of the conveyor belts 441, 451, and 461.

[0090] The first pre-fixing conveyance section 460 is supported so as to be swingable relative to the housing 108a of the intermediate conveyance section 108. The components of the first pre-fixing conveyance section 460 are similar to those of the pre-fixing conveyance section 410 described in the first embodiment. However, in this embodiment, unlike the first embodiment, the first pre-fixing conveyance section 460 is supported by the housing 108a of the intermediate conveyance section 108.

[0091] That is, the first pre-fixing conveyance section 460 is supported by a swing support section 465 so as to be swingable relative to the housing 108a about a swing axis α that is along the sheet width direction that intersects with (orthogonal to) the sheet conveyance direction FD (in this embodiment, perpendicular to) the sheet conveyance direction FD. The configuration of the swing support section 465 is the same as that of the swing support section 415 in the first embodiment. The first pre-fixing conveyance section 460 also has a contact section 466 that at least a portion of which enters the housing 103b when the housings 108a and 103b are connected to each other. The configuration of the contact section 466 is the same as that of the contact section 416 in the first embodiment.

[0092] On the other hand, a positioning member 131a is provided in the housing 103b. The positioning member 131a abuts against a contact portion 466 provided on a part of the first pre-fixing conveyance section 460, thereby positioning the first pre-fixing conveyance section 460 in the swing direction around the swing axis α. The positioning member 131a has the same configuration as in the first embodiment, and is attached to a fixing conveyance section support 132 provided on the surface of the housing 103b that meets the housing 108a, in the same phase as the abutment portion 466 in the sheet width direction.

[0093] Furthermore, the components provided in the fixing conveying section 103 and the fixing section 50 are also the same as those described in the first embodiment. Here, the angle and width of the guide surface 53a of the fixing entrance guide 53 are set so that the leading edge of the sheet will contact the guide surface of the fixing entrance guide 53 even if there is variation in the angle of the sheet conveying surface 430a due to variation in tolerance in the height direction from the contact portion 466 to the sheet conveying surface 460a of the first pre-fixing conveying section 460 or variation in the sheet posture due to upward or downward curling of the leading edge of the sheet.

[0094] The positioning behavior of the first pre-fixing conveyance section 460 when the housings 108a and 103b are brought close to each other and connected is also the same as the configuration described in the first embodiment. However, it differs from the first embodiment in that the swing restricting member is fixedly supported by the housing 108a. With the above configuration, when the housings 108a and 103b are connected, the first pre-fixing conveyance section 460 swings smoothly, the height is determined, and the guide surface 53a of the fixing inlet guide 53 and the imaginary line 460a' of the sheet conveyance surface 460a of the first pre-fixing conveyance section 460 intersect at an appropriate point.

[0095] As described above, in this embodiment, in addition to the effects described in the second embodiment, it is possible to improve image quality even for 30-inch (762 mm) sheets, which are often used as long sheets. That is, an intermediate conveying section 108 is added between the secondary transfer nip section N1 and the fixing nip section N2, so that the sheet is conveyed via the third pre-fixing conveying section 450. As a result, a sufficient distance can be secured between the secondary transfer nip section N1 and the fixing nip section N2, and image defects caused by the sheet being nipped by the secondary transfer nip section N1 and the fixing nip section N2 simultaneously can be suppressed even when a long sheet is conveyed.

[0096] In this embodiment, the distance between the secondary transfer nip N1 and the fixing nip N2 is set to approximately 800 mm, but if a longer sheet is to be used, another intermediate conveyance unit may be added between the secondary transfer nip N1 and the fixing nip N2 to increase the number of pre-fixing conveyance units between the secondary transfer nip N1 and the fixing nip N2. In this case, the pre-fixing conveyance unit located most downstream in the sheet conveyance direction FD between the secondary transfer unit and the fixing unit 50 has a support configuration and positioning configuration similar to the pre-fixing conveyance unit 410 of the first embodiment.

[0097] The configuration of this embodiment may be applied to the configuration of the first embodiment. That is, the intermediate conveying unit 108 may be added between the image forming unit 102 and the fixing and conveying unit 103. In other words, in the configuration shown in Figures 11 and 12, the second pre-fixing conveying unit 440 may be omitted, and the sheet may be directly conveyed from the transfer guide 219 to the third pre-fixing conveying unit 450. [Explanation of symbols]

[0098] 50 Fixing section 51 Heating roller (first rotating body) 52: Opposing roller (second rotating body) 53 Fixing entrance guide 102a···First enclosure 102b... Enclosure (third enclosure) 103a...Second housing 103b... Enclosure (second enclosure) 108a···Case (first case) 131a... Positioning member 221....Swing control part 410 Pre-fixing transport section (transport section) 411, 431, 461...Conveyor belt (belt) 412, 432, 462... Drive rollers (tension members) 412a, 412b, 412c, 432a, 432b, 432c, 462a, 462b, 462c... Driven rollers (tension members) 413, 433, 463: Drive motor (drive means) 414, 434, 464....Suction fan (air suction section) 415, 435, 465... Swing support part 415a... First swing support member (first support member) 415b... Second swing support member (second support member) 416, 436, 466...Contact part 416a···Locating surface 416b Guideway 420, 440: Second pre-fixing transport section (second transport section) 430, 460: First pre-fixing transport section (first transport section) 450 Third pre-fixing transport section (third transport section)

Claims

1. a transfer section for transferring the toner image onto a sheet; a fixing section for fixing the toner image transferred to the sheet by the transfer section onto the sheet; a belt suction conveying unit disposed between the transfer unit and the fixing unit in a sheet conveying direction, the belt suction conveying unit having a belt unit and a suction unit that sucks air to suck the sheet to the belt unit, the belt suction conveying unit rotating the belt unit to convey the sheet sucked by the belt unit toward the fixing unit; A first housing; a second housing connected to the first housing and supporting the fixing unit; the first housing has a first positioning portion that positions the belt suction conveying portion in a predetermined direction along a plane perpendicular to a width direction of the sheet that is perpendicular to the sheet conveying direction, The second housing has a second positioning portion that positions the belt suction conveying portion in the predetermined direction.

1. An image forming apparatus comprising:

2. the predetermined direction is a vertical direction, The image forming apparatus according to claim 1 , wherein the first positioning unit performs positioning in a horizontal direction in addition to the predetermined direction.

3. the first positioning portion is provided in the belt suction conveying portion and includes a swing shaft that swings about an axis extending in a sheet width direction intersecting with the sheet conveying direction, and a hole that is provided in the first housing and engages with the swing shaft; 3. The image forming apparatus according to claim 1, wherein the second positioning portion is composed of a contact portion provided in the belt suction transport portion and a contacted portion provided in the second housing against which the contact portion contacts.

4. The abutted portion is a driven roller, 4. The image forming apparatus according to claim 3, wherein when the second housing is connected to the first housing, the belt suction transport section is guided into the inside of the second housing by the driven roller abutting against the abutment portion of the belt suction transport section and rotating, and is positioned in the specified direction by oscillating around the oscillating axis.

5. 5. The image forming apparatus according to claim 3, wherein the contact portion has a positioning surface that contacts the contacted portion to position it in the specified direction, and a guide surface that guides the contacted portion toward the positioning surface when the second housing is connected to the first housing.

6. 6. The image forming apparatus according to claim 3, wherein the contact portion is provided so that a position of the contact portion in the predetermined direction is adjustable with respect to the second housing.

7. a pre-fixing guide having a guide surface that guides the sheet conveyed by the belt suction conveying unit toward the fixing unit, 7. The image forming apparatus according to claim 1, wherein the guide surface intersects with an imaginary line that extends from a conveying surface of the belt portion, which attracts and conveys the sheet, toward the guide surface.

8. 8. The image forming apparatus according to claim 1, wherein the transfer unit is supported by the first housing.

9. An image forming apparatus as described in any one of claims 1 to 8, characterized in that when the belt suction conveying section is a first conveying section, the image forming apparatus further comprises a second conveying section that is arranged between the first conveying section and the transfer section in the sheet conveying direction and conveys the sheet onto which the toner image has been transferred in the transfer section toward the first conveying section.

10. 10. The image forming apparatus according to claim 9, wherein the second transport section is supported so as to be insertable and removable from the first housing.

11. A third housing supporting the transfer unit; a third conveying unit disposed between the first conveying unit and the second conveying unit in the sheet conveying direction and configured to convey the sheet from the second conveying unit toward the first conveying unit, 11. The image forming apparatus according to claim 9, wherein the first housing is disposed between the third housing and the second housing in the sheet transport direction and is connected to the third housing and the second housing, respectively.

12. the swing shaft includes a first swing shaft and a second swing shaft that swingably support the belt suction conveyance unit on both sides of the belt suction conveyance unit in the sheet width direction, The hole portion has a first hole portion that engages with the first swing shaft and a second hole portion that engages with the second swing shaft.

7. The image forming apparatus according to claim 3, wherein the image forming apparatus further comprises a first fixing unit.

13. the belt suction conveying unit has a swing regulating unit that is capable of regulating a swing range around the swing shaft when the first housing is not connected to the second housing, The range of the swinging movement by the swinging movement restricting portion is configured so that the abutted portion can abut against the abutting portion when the first housing is connected to the second housing.

13. The image forming apparatus according to claim 3, wherein the image forming apparatus further comprises a first fixing unit.

Images