JP7806433B2 - Sheet conveying device and image forming apparatus - Google Patents

Description

This disclosure relates to a sheet conveying device having an endless belt and an image forming apparatus having the sheet conveying device.

Electrophotographic image forming devices are equipped with a fixing device that thermally fixes a sheet carrying an unfixed toner image by passing it through a nip formed between a heating rotor and a pressure rotor.

In recent years, in order to save energy, belt-type fixing devices have become increasingly popular. In these devices, a fixing belt (endless belt) is stretched between a heating roller, which serves as a heat source, and a long support such as a support pad or support roller (fixing roller), and the fixing belt is sandwiched between the support and a pressure roller to form a nip.

The fixing belt is made primarily from metal or resin materials, is relatively thin, and has a low heat capacity, which shortens the time it takes to heat up to the fixing temperature when the device is started up or from standby mode, contributing to energy savings.

Figure 11 is a cross-sectional view showing an example of the configuration of a conventional fixing device that uses a fixing belt. As shown in the figure, a fixing belt 531, a pressure roller 532, a fixing pad 533, a heating roller 534, etc. are arranged within the fixing device housing 538.

The fixing belt 531 is stretched between the fixing pad 533 and the heating roller 534, and the portion of the fixing belt 531 that corresponds to the fixing pad 533 is pressed against the pressure roller 532 to form a nip portion Np.

The pressure roller 532 is driven to rotate in the direction of arrow Q by a drive source (not shown), which causes the fixing belt 531 to move in the direction of arrow P, and the heating roller 534 also rotates in conjunction with the fixing belt 531.

A heater 535 is built into the heating roller 534, which heats the fixing belt 531. A recording sheet with an unfixed toner image formed on it is passed through the nip portion Np and thermally fixed.

Downstream of the nip portion Np in the paper passage direction (bottom to top in Figure 11), a pair of paper passage guides 536, 537 are arranged to guide the sheet that has passed through the nip portion Np toward the outlet 539 of the fixing device housing 538.

Figure 12(a) is an external perspective view of the paper passing guide 536 as seen from slightly to the right of Figure 11.

As shown in the figure, the paper passage guide 536 has a plate-shaped guide body 5361 that is long in the width direction of the fixing belt 531 (a direction perpendicular to the running direction), and multiple ribs 5362 that are erected parallel to the sheet passage direction on the surface facing the sheet.

Figure 12(b) is an enlarged view of the area surrounded by the semicircular dashed line J5 in Figure 12.

The rib 5362 is provided to reduce the contact area with the sheet and guide the sheet toward the discharge port of the housing 538, so it is designed with a narrow width W11 of approximately 1 mm and a height H11 of approximately 2 mm.

The lower end of the rib 5362 is positioned close to the surface of the fixing belt 531 so that the leading edge of the sheet that has passed through the nip portion Np in close contact with the fixing belt 531 is picked up by the sheet's stiffness at a position where it separates from the fixing belt 531 and guides the sheet upward.

Japanese Patent Application Laid-Open No. 2004-93582

However, when rotating the fixing belt 531, particularly when the image forming apparatus is turned on and started up at the beginning of the day, if the fixing belt 531 is not yet sufficiently heated and is rotated by the pressure roller 532, the rigidity of the fixing belt 531 is still high, and the rotational torque becomes unstable due to factors such as static friction at the bearing portion of the heating roller 534, making the behavior of the fixing belt 531 unstable, which can cause the fixing belt 531 to float downstream of the fixing nip Np (the portion indicated by the dashed line 531a in Figure 11; hereinafter referred to as "belt floating").

If even a small amount of belt lift occurs, the fixing belt 531 will come into contact with the lower end (the end on the nip portion Np side) of the paper guide 536, which is positioned close to the fixing belt 531.

As mentioned above, the width W11 of the rib 5362 is not particularly large. Therefore, when the fixing belt 531 comes into contact with the lower end of the rib 5362, particularly the corner 5362a (Figure 12(b)), numerous fine scratches 531b are created on the surface of the fixing belt 531, as shown in Figure 12(c). This causes problems such as gloss streaks to appear in the fixed image, degrading image quality.

To solve this problem, for example, Patent Document 1 proposes a configuration in which a drive roller is brought into contact with the fixing roller via the fixing belt on the downstream side of the nip portion Np in the paper feed direction, and the peripheral speed of the drive roller is rotated so that it is faster than the peripheral speed of the fixing belt, thereby applying tension to the fixing belt in a direction that eliminates belt lift, thereby suppressing belt lift.

However, providing a separate drive roller as in Patent Document 1 increases the size of the device, increases the number of parts, and increases manufacturing costs.

The issue of preventing belt deterioration due to contact with the paper guide ribs is not limited to the fixing device described above, but can occur in general sheet conveying devices that have a structure in which a sheet is conveyed by passing it through a nip formed by pressing a rotating body against an endless belt, and a paper guide is arranged adjacent to the endless belt downstream of the nip.

This disclosure has been made in consideration of the above circumstances, and aims to provide a sheet conveying device with an endless belt that can prevent damage to the endless belt even if the belt floats, without increasing the size of the device, with a simple configuration that is low in cost, and an image forming apparatus equipped with such a sheet conveying device.

In order to achieve the above-mentioned object, a sheet conveying device according to one aspect of the present disclosure is a sheet conveying device in which an endless belt is pressed and clamped between a long support body and a rotating body to form a nip portion, and a sheet is passed through the nip portion to be conveyed, and is provided with a guide member that guides a sheet that has been discharged from the nip portion toward the endless belt, and the guide member has a plurality of ribs extending along the sheet conveying direction arranged side by side on the sheet guide surface side of the guide main body in a direction perpendicular to the sheet conveying direction, and a belt protection member that is at least the same height as the tip of the ribs and wider than the tip is provided along the nip side edge of the guide main body , and the rib has a first portion on the upstream side and a second portion on the downstream side, and in a side view, the ridge of the top of the first portion that contacts the sheet is shaped to retreat in a direction away from the sheet conveying path as it moves upstream from the boundary with the second portion to the tip of the nip side .

In one aspect of the present disclosure, the belt protection member is formed as a single continuous piece along the edge of the guide body on the nip side.

In addition, a sheet conveying device according to another aspect of the present disclosure is a sheet conveying device in which an endless belt is pressed and clamped between a long support body and a rotating body to form a nip portion, and a sheet is passed through the nip portion to be conveyed, and is provided with a guide member that guides a sheet that has been discharged from the nip portion toward the endless belt, and the guide member has a plurality of ribs extending along the sheet conveying direction arranged side by side on the sheet guide surface side of the guide main body in a direction perpendicular to the sheet conveying direction, and a belt protection member that is at least the same height as the tip of the rib and wider than the tip is provided along the nip side edge of the guide main body at a position closer to the nip portion than the nip side tip of the plurality of ribs, and the belt protection member is provided in multiple sections along the nip side edge of the guide main body, and

In one aspect of the present disclosure, the tip of the rib and the belt protection member are integrally formed, and the tip of the rib on the nip side is connected to the belt protection member to form a T-shape, and/or the tip of the nip side of two adjacent ribs is connected to each other via the belt protection member to form a U-shape.

In addition, a sheet conveying device according to another aspect of the present disclosure is a sheet conveying device in which an endless belt is pressed and sandwiched between a long support body and a rotating body to form a nip portion, and a sheet is passed through the nip portion to be conveyed, and is provided with a guide member that guides a sheet that has been discharged from the nip portion toward the endless belt, and the guide member has a plurality of ribs that extend along the sheet conveying direction and are arranged side by side in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide main body, and a belt protection member that is at least the same height as the tips of the ribs and wider than the tips is provided along the nip side edge of the guide main body at a position closer to the nip portion than the nip side tips of the plurality of ribs, and the belt protection member is arranged so that when there is no floating in the endless belt, the distance between the surface of the belt protection member facing the endless belt and the surface of the endless belt is greater at a second position farthest from the nip portion than at a first position on the facing surface closest to the nip portion.

In another aspect of the present disclosure, the guide member is formed of a resin material .

Another aspect of the present disclosure is a sheet conveying device in which an endless belt is clamped and pressed between a long support body and a rotating body to form a nip portion, and a sheet is passed through the nip portion for conveyance. The device includes a guide member that guides a sheet that has been discharged from the nip portion toward the endless belt. The guide member has multiple ribs that extend along the sheet conveyance direction and are arranged in a direction perpendicular to the sheet conveyance direction on the sheet guide surface side of the guide body, and the width of the tips of the multiple ribs on the nip side in the direction perpendicular to the sheet conveyance direction is 6 mm or more and 11 mm or less.

In addition, a sheet conveying device according to another aspect of the present disclosure is a sheet conveying device that forms a nip portion by pressing an endless belt between a long support body and a rotating body, and conveys a sheet by passing it through the nip portion, and is equipped with a guide member that guides a sheet that has been discharged from the nip portion toward the endless belt, and the guide member has a plurality of ribs that extend along the sheet conveying direction and are arranged side by side in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide body, and a belt protection member that is at least the same height as the tip ends of the ribs and wider than the tip ends is provided along the nip side edge of the guide body at a position closer to the nip portion than the nip side tips of the plurality of ribs, and the endless belt is a fixing belt, and is equipped with a heating means for heating the fixing belt.

In addition, a sheet conveying device according to another aspect of the present disclosure is a sheet conveying device in which an endless belt is pressed and sandwiched between a long support body and a rotating body to form a nip portion, and a sheet is passed through the nip portion to be conveyed, and is provided with a guide member that guides a sheet that has been discharged from the nip portion toward the endless belt, and the guide member has a plurality of ribs that extend along the sheet conveying direction and are arranged side by side in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide body, and a belt protection member that is at least the same height as the tips of the ribs and wider than the tips is provided along the nip side edge of the guide body at a position closer to the nip portion than the nip side tips of the plurality of ribs, and the endless belt is an image carrying belt that carries a toner image, and the rotating body is a transfer roller that transfers the toner image carried on the surface of the image carrying belt to a sheet that is passed through the nip portion between the image carrying belt and the rotating body.

Another aspect of the present disclosure is an image forming apparatus equipped with the above-described sheet conveying device.

The configuration of the sheet conveying device according to the above-disclosed aspect makes it less likely for the endless belt surface to be damaged, even if the endless belt floats, because a belt protection member is provided that has a larger contact area with the endless belt than the end surface of the lower end of the rib of a conventional paper feed guide. Furthermore, since there is no need to provide a drive roller to prevent the belt from floating, as in Patent Document 1, the device does not become larger, and the configuration is simple and inexpensive.

1 is a schematic diagram illustrating the overall configuration of a printer equipped with a fixing device according to one embodiment of the present disclosure. FIG. 2 is a cross-sectional view illustrating a configuration of a fixing unit of the printer. 1A is a perspective view of a first embodiment of a belt-side paper guide in a fixing device according to an aspect of the present disclosure, and FIG. 1B is a partially enlarged view thereof; 10A and 10B are diagrams for explaining the effects of the belt-side paper guide. 1A is a perspective view of a second embodiment of a belt-side paper guide in a fixing device according to an aspect of the present disclosure, and FIG. 1B is a partially enlarged view thereof; 10A is a perspective view of a third embodiment of a belt-side paper guide in a fixing device according to an aspect of the present disclosure, and FIG. 10B is a partially enlarged view thereof; 1A is an explanatory diagram of mold splitting when injection molding a belt-side paper-passage guide according to the present disclosure, and FIG. 1B is an explanatory diagram of mold splitting when injection molding a conventional belt-side paper-passage guide. 10A and 10B are diagrams illustrating the size of a gap between a fixing belt and a belt protection member of a belt-side paper-passing guide according to the present disclosure. 1A is a perspective view of a modified belt-side paper guide in a fixing device according to an embodiment of the present disclosure, and FIG. 1B is a partially enlarged view thereof. 10A and 10B are diagrams illustrating a modified example in which the configuration of the sheet conveying device according to an embodiment of the present disclosure is applied to a secondary transfer unit. 1A and 1B are diagrams for explaining problems with a conventional belt-type fixing device. 1A is a perspective view of a paper guide on the belt side in the conventional fixing device, FIG. 1B is a partially enlarged view thereof, and FIG. 1C is a diagram showing an example of scratches that have occurred on the surface of the fixing belt.

The following describes, with reference to the drawings, a fixing device to which the structure of a sheet conveying device according to an embodiment of the present disclosure is applied, and a tandem color printer (hereinafter simply referred to as "printer") as an example of an image forming apparatus having such a fixing device.

(1) Overall Configuration of the Printer FIG. 1 is a schematic cross-sectional view showing the overall configuration of a printer 1.

As shown in the figure, the printer 1 is an electrophotographic printer that includes a feed unit 10, an image creation unit 20, a fixing unit 30, a discharge unit 40, and a duplex conveyance unit 50, and is capable of executing a single-sided print job in which an image is printed on only one side (the front side) of a recording sheet S for recording, and a double-sided print job in which an image is printed on both sides (the front and back sides) of the recording sheet S.

The feeding unit 10 includes a paper feed tray 11 that stores recording sheets S, a feed roller 12P that is provided in the paper feed tray 11 and feeds the recording sheets S one by one toward the transport path 19, a paper feed roller 12F that feeds and transports the fed recording sheets S, and a timing roller 13 that determines the timing for sending the recording sheets S to the secondary transfer position 29.

The imaging unit 20 forms a toner image on the recording sheet S fed from the feeding unit 10. Specifically, the four imaging units 21Y, 21M, 21C, and 21K expose the surfaces of the charged photosensitive drums 25Y, 25M, 25C, and 25K to laser light from the exposure unit 26, which is modulated and driven based on image data, to create an electrostatic latent image on the surface, which is then developed with toner of each color: yellow (Y), magenta (M), cyan (C), and black (K).

The four-color toner images visualized by development are primarily transferred from the surface of each photosensitive drum onto the surface of intermediate transfer belt 23 by the electric field between photosensitive drums 25Y, 25M, 25C, and 25K and primary transfer rollers 22Y, 22M, 22C, and 22K that face these drums via intermediate transfer belt 23. During this primary transfer, the timing of toner image formation in imaging units 21Y-21K is staggered so that each Y-K toner image is transferred to the same position on intermediate transfer belt 23. This forms a color toner image on intermediate transfer belt 23 in which the Y-K toner images are multiplexed.

Intermediate transfer belt 23 is located above photosensitive drums 25Y-25K, stretched over multiple rollers including drive roller 23R and driven roller 23L, and rotates in the direction of arrow A. As intermediate transfer belt 23 rotates, the color toner image on intermediate transfer belt 23 moves to secondary transfer position 29, where intermediate transfer belt 23 contacts secondary transfer roller 24. Secondary transfer roller 24 is urged toward intermediate transfer belt 23 by a urging means (not shown), generating a predetermined nip pressure between the two.

At secondary transfer position 29, the color toner image on intermediate transfer belt 23 is secondarily transferred to the surface (first side) of recording sheet S, which has been conveyed from feed unit 10, by the electric field between intermediate transfer belt 23 and secondary transfer roller 24 when the recording sheet S passes between intermediate transfer belt 23 and secondary transfer roller 24. Any toner remaining on intermediate transfer belt 23 during this secondary transfer is removed by cleaning blade 23B.

The recording sheet S onto which the color toner image (unfixed image) has been secondarily transferred is transported in the direction of arrow E by the secondary transfer roller 24 toward the fixing unit 30.

The fixing unit 30 includes a fixing belt (endless belt) 31 and a pressure roller (rotating body) 32. When a recording sheet S is passed through the nip Np formed between the two, the color toner image is thermally fixed onto the recording sheet S.

The discharge section 40 includes a discharge roller 41 and a paper discharge port 45, and discharges the recording sheet S with the fixed color toner image from the paper discharge port 45. The discharge roller 41 is positioned inside the paper discharge port 45 and rotates in the direction of arrow B (forward), transporting the recording sheet S transported from the fixing section 30 through the paper discharge port 45 and discharging it outside the machine. The discharged paper S is stored in the paper discharge tray 46. This completes single-sided printing, in which only the first side of the recording sheet S is printed.

In addition, in the case of a double-sided print job, the recording sheet S that has passed the secondary transfer position 29 during printing on the front side (first side) is transported from the fixing unit 30 to the discharge rollers 41. When the trailing edge of the recording sheet S being transported by the discharge rollers 41 passes the detection position of the discharge sensor ES, which is an optical sensor, the discharge rollers 41 switch from forward rotation to reverse rotation (rotation in the direction of arrow C).

This reversal of the discharge roller 41 causes the recording sheet S to be inverted and guided to the double-sided conveying section 50, where it is transported along the double-sided conveying path in the direction of arrow D by double-sided conveying rollers 51, 52, 53, 54, and 55, and then transported again to the secondary transfer position 29 via timing roller 13. The color toner image is secondarily transferred onto the back side (second side) of the recording sheet S, and after being thermally fixed in the fixing section 30, it is discharged via the discharge roller 41 to the paper output tray 46.

In the feed unit 10 and imaging unit 20, rotating members including paper feed and transport rollers, drive roller 23R, and photosensitive drums 25Y-25K are rotated by the driving force of drive motor M1 arranged in the imaging unit 20. Furthermore, the pressure roller 32 in the fixing unit 30 is driven to rotate by drive motor (fixing motor) M2, the discharge roller 41 rotates forward and reverse by the driving force of drive motor M3 arranged in the discharge unit 40, and the duplex transport rollers 51-55 are rotated by the driving force of drive motor M4 arranged in the duplex transport unit 50.

The control unit 100 is also connected to an external terminal device via a network, receives print job data sent from this terminal device, generates image data to be printed from the received print job data, and provides the generated image data for printing.

(2) Configuration of Fixing Unit FIG. 2 is a cross-sectional view showing the configuration of the fixing unit 30. As shown in FIG.

As shown in the figure, the fixing unit 30 has a fixing belt 31 stretched between a heating roller 34 (heating unit) and a fixing pad (support) 33, and a pressure roller 32 pressed against the fixing pad 33 to form a nip.

In Figure 2, the direction of the axis of the heating roller 34 (longitudinal direction) is the X-axis, the vertical direction is the Z-axis, and the direction perpendicular to the XZ-axis is the Y-axis (the same applies to the following drawings).

In this embodiment, the fixing pad 33 is made of resin, is elongated in a direction parallel to the axis of the heating roller 34 (X-axis direction), and abuts against the back surface of the fixing belt 31 to support it. The fixing pad 33 is fixed to the housing 38 via a support member 331.

It is desirable to apply a surface treatment and/or lubricant to the surface of the fixing pad 33 that comes into contact with the fixing belt 31 to reduce friction.

The fixing belt 31 is composed of a base layer made of, for example, polyimide or SUS (stainless steel), on which an elastic layer made of a highly heat-resistant material such as silicone rubber or fluororubber, and a release layer made of a fluorine-based resin such as PFA (perfluoroalkoxy fluororesin) with releasability are layered in this order.

The pressure roller 32 has an elastic layer 322 made of a highly heat-resistant elastic material such as silicone rubber laminated on the outer surface of a cylindrical core 321 made of aluminum, iron, or the like. A release layer (not shown) such as PFA may be laminated on the outermost layer.

The pressure roller 32 is pressed against the outer surface of the fixing belt 31 with a predetermined load (pressure) due to the biasing force of an elastic member (not shown), such as a spring. This pressure contact forms a nip Np between the outer surface of the pressure roller 32 and the outer surface of the fixing belt 31.

The pressure roller 32 is driven to rotate at a predetermined rotational speed in the direction of arrow Q by the rotational drive force of the fixing motor M2 (Figure 1), and functions as a drive roller. The rotation of this pressure roller 32 causes the heating roller 34 and the fixing belt 31, which is stretched between the heating roller 34 and the fixing pad 33, to rotate (run) in the direction of arrow P.

The heating roller 34 is, for example, made by laminating a coating layer made of PTFE (polytetrafluoroethylene) on the outer surface of a cylindrical aluminum hollow core, and both axial ends of the roller are rotatably supported by the frame of the housing 38 of the fixing unit 30.

A heater unit 341 is inserted into the inner periphery of the cylindrical heating roller 34, and consists of a first heater 3411 that heats almost the entire axial range of the heating roller 34 (longitudinal direction: X-axis direction in Figure 2), and a second heater 3412 that heats the central portion in the axial direction. The heater unit 341 generates heat when supplied with power from a power source (not shown), thereby heating the heating roller 34.

The heating roller 34 is held in a long hole (not shown) in the frame of the housing 38 via a bearing member 342. The long diameter of the long hole is inclined diagonally to the right in the figure, and by biasing the bearing member 342 diagonally downward to the left with an elastic member 343 such as a compression spring, the heating roller 34 is biased in a direction away from the fixing pad 33, and a predetermined amount of tension is applied to the fixing belt 31.

When the heater section 341 is energized while the fixing belt 31 is rotating, heat emitted from the heater section 341 is transferred from the heating roller 34 to the fixing belt 31, and reaches the nip section Np as the fixing belt 31 rotates.

As a result, heat from the fixing belt 31 is supplied to the pressure roller 32 and the fixing pad 33, causing the temperature of the nip portion Np, which is the contact area between the fixing belt 31 and the pressure roller 32, to rise.

A temperature sensor (not shown) is located near the portion of the fixing belt 31 that contacts the outer surface of the heating roller 34, and detects the surface temperature of the fixing belt 31. Based on the detection results, the control unit 100 turns the power supplied to the heater unit 341 on and off to control the fixing belt 31 to reach the target temperature.

The recording sheet with the toner image transferred passes through the nip portion Np with the surface with the transferred toner image facing the heated fixing belt 31. The recording sheet passing through the nip portion Np is pressed and heated by being sandwiched between the fixing belt 31 and the pressure roller 32, and the toner image is fixed to the recording sheet.

A pair of entrance-side paper guide members 391, 392 are arranged upstream of the nip portion Np in the sheet transport direction, and guide the recording sheet S that has passed through the secondary transfer position 29 toward the nip portion Np.

In addition, a pair of outlet-side paper guide members 36, 37 are arranged downstream of the nip portion Np in the sheet transport direction, and guide the recording sheet S that has passed through the nip portion Np toward the outlet 381 of the housing 38 of the fixing unit 30.

When a recording sheet S passes through the nip Np, the fused toner adheres to the surface of the fixing belt 31, and it tends to be discharged while leaning toward the fixing belt 31. Because the surface of the fixing belt 31, supported by the fixing pad 33 downstream of the nip Np, has a large curvature, the stiffness of the recording sheet S causes the leading edge of the recording sheet S to lift off the surface of the fixing belt 31. This is then picked up and guided upward by the leading edge 3631 (see Figure 4) of the fixing belt 31-side paper guide 36 (hereinafter referred to as the "belt-side paper guide 36") on the nip Np side (this process of scooping up the leading edge of the recording sheet from the fixing belt by the belt-side paper guide is hereinafter referred to as the "scooping function").

To effectively utilize the scooping function, it is desirable to minimize the distance between the leading edge 3631 of the belt-side paper guide 36 and the surface of the fixing belt 31 when the belt is stopped (when there is no belt lift). Otherwise, thin sheets, in particular, have weak stiffness, so the leading edge will only lift up a small amount, and the sheet will be caught in the fixing belt 31, causing problems. In this embodiment, the distance is approximately 1 to 2 mm, but this is not limited to this and can be positioned as close as possible to enable the scooping function to be utilized depending on the device specifications (the curvature of the fixing belt 31 immediately after passing through the nip portion Np defined by the fixing pad 33, the type of sheet used, the material of the fixing belt 31, etc.).

However, when the fixing belt 31 is placed in such close proximity, if its behavior is unstable, such as when the device is started up, the fixing belt 31 will float as described above and come into contact with the lower end of the rib on the belt-side paper guide.

As mentioned above, conventionally, this rib was small in width and had relatively sharp corners at its bottom end that faced the fixing belt 31, causing scratches on the surface of the fixing belt 31 and resulting in image quality degradation such as gloss streaks. Therefore, in this embodiment, a belt protection member is provided along the lower edge of the belt-side paper guide 36 to increase the contact area with the fixing belt 31, preventing the surface of the fixing belt 31 from being scratched even if the belt floats.

When a double-sided print job is performed, when a recording sheet S with a toner image formed on its first side (front side) passes through the nip portion Np to fix the toner image on its second side (back side), the toner image formed on the first side may cause the recording sheet S to adhere to the pressure roller 32. Therefore, in this embodiment, a separation claw 371 is provided on the paper passing guide 37 side.

(3) Belt Protection Member Three examples of the belt protection member in the belt-side sheet-passing guide according to this embodiment will be described below.

(3-1) First embodiment of belt protection member Figure 3(a) is a perspective view of the belt-side paper guide 36 according to this embodiment when viewed from the front right of Figure 2, and Figure 3(b) is an enlarged view of the area surrounded by dashed line J1 in Figure 3(a).

As shown in Figure 3(a), the belt-side paper guide 36 has a plate-shaped guide body 361 that is long in the X direction. On the sheet guide surface side (the surface that guides the recording sheet S) of the guide body 361, multiple ribs 362 that extend in the direction E along the conveyance direction E of the recording sheet S (see Figure 1) are arranged in parallel in the longitudinal direction (X direction).

The ribs 362 are positioned in the X direction at positions necessary to guide at least the central periphery and both ends in the width direction for each of the multiple sizes of recording sheets S that can be used with the printer 1.

In this embodiment, a belt protection member 363 is formed integrally with the rib 362 along the lower edge 3611 of the belt-side paper guide 36 at a position closer to the nip portion Np than the lower end of the rib 362 (the tip on the nip portion Np side), forming a T-shape when viewed upside down from the Y-axis direction.

In this embodiment, the height of the belt protection member 363 (height from the guide-side surface of the guide body 361) is set equal to the height of the lower end (tip end on the nip side) of the rib 362, but it may be higher. In this case, the upper limit of the height can be determined by a person skilled in the art through design or experimentation, taking into account design specifications such as the installation space for the belt-side paper guide 36 within the housing 38, and the need for the belt-side paper guide 36 to function as a scoop up the leading edge of the recording sheet S.

Furthermore, the width of the belt protection member 363 (width in the X-axis direction) should be greater than the width of the lower end of the rib 362, and preferably be 5 mm or more.

If it is at least wider than the width of the rib 362, the contact area with the fixing belt 31 can be increased when the belt lifts, and scratches on the fixing belt 31 can be reduced more than before.

It is desirable that the surface 3632 of each belt protection member 363 facing the fixing belt 31 is flat and on the same plane as the lower edge 3611.

Figure 4 is a diagram illustrating the effect of providing a belt protection member 363 on the belt-side paper guide 36 in the fixing unit 30. For simplicity, the paper guide 37 and other components are omitted from the illustration.

As shown in Figure 4, even if belt lift 31a occurs on the fixing belt 31 when starting up the printer 1, the belt contacts the flat opposing surface 3632 of the belt protection member 363, which has a larger area than the end area of the conventional rib 362. This prevents scratches on the surface of the fixing belt 31 and prevents degradation of the fixed image.

It is desirable that the positions of the multiple ribs 362 and the length in the X-axis direction of each belt protection member 363 be symmetrical with respect to the paper passing center (center in the X-axis direction) M (Figure 3(a)) in the sheet transport path. This is because the contact resistance with the recording sheet S is symmetrical in the sheet width direction across the paper passing center M, allowing the recording sheet S to be transported smoothly without skewing.

(3-2) Second embodiment of belt protection member In the first embodiment, the belt protection member 363 is integrally provided at the tip of the rib 362 to form a T-shape, but in the second embodiment, multiple belt protection members are connected in a single line in the X direction.

Figure 5(a) is a perspective view of the belt-side paper guide 36 according to the second embodiment, viewed from the same direction as Figure 3(a), and Figure 5(b) is an enlarged view of the area surrounded by dashed line J2 in Figure 5(a).

As shown in Figure 5(a), the belt protection member 364 in this embodiment has the shape of a single belt protection member 363 connected in the X direction, as in the first embodiment.

In this embodiment, the height of the belt protection member 364 only needs to be at least the height of the lower end of the rib 362.

In this second embodiment, the area of the facing surface 3642 of the belt protection member 364 that faces the fixing belt 31 is increased, making it possible to significantly increase the contact area with the belt floating portion 31a of the fixing belt 31 compared to the first embodiment, thereby further enhancing the effect of preventing scratches on the fixing belt 31.

On the other hand, if the belt protection member 364 is formed in the shape of a single rib along the lower edge of the belt-side paper guide 36, the thickness of that edge will be thick over almost the entire X-direction. Therefore, when manufacturing using injection molding, there is a risk of "warping" in the X-axis direction due to variations in the cooling rate in the longitudinal direction.

The effect of "warping" in the X direction can cause variations in the gap in the X direction between the lower edge of the belt-side paper guide 36 and the fixing belt 31, which could prevent the belt from fully functioning as it scoops up the leading edge of the recording sheet S and guides it rearward. Therefore, when manufacturing by injection molding, it is advisable to determine the dimensions of the belt protection member 364 (height and width in the sheet transport direction) taking into account the characteristics of the resin material used and the allowable range of gap variations required to ensure the scooping function.

Note that the belt protection member 364 does not necessarily need to be continuous across all of the ribs 362, and may be separated at any appropriate point other than where the tips of the ribs 362 are located.

(3-3) Third embodiment of belt protection member Figure 6(a) is a perspective view of the belt-side paper guide 36 according to the second embodiment when viewed from the same direction as Figure 3(a), and Figure 6(b) is an enlarged view of the area surrounded by the dashed line J3 in Figure 6(a).

In this third embodiment, in addition to forming the belt protection member 363 in a T-shape relative to the rib 362 as shown in Figures 3(a) and (b), it is also possible to form a belt protection member 365 that is U-shaped when viewed from the Y-axis direction by connecting the tips of two adjacent ribs 362, as shown in Figures 6(a) and (b).

When combining the T-shaped belt protection member 363 (Figure 3(b)) and the U-shaped belt protection member 365, it is desirable to position them symmetrically with respect to the paper passing center M. This is because the amount of contact friction between the belt protection member and the recording sheet S is also symmetrical, and it is believed that this allows the recording sheet S to be guided more smoothly along the conveyance direction than if they were positioned randomly.

(4) Manufacturing Method of Belt-Side Paper Passage Guide In this embodiment, the belt-side paper pass guide 36 is manufactured by injection molding from the viewpoint of manufacturing costs.

In injection molding, synthetic resin (plastic) or other resin material is heated and melted, injected into a mold, and then cooled to form the desired shape. Injection molding allows for the continuous mass production of complex-shaped parts, making it advantageous in terms of manufacturing costs.

Figures 7(a) and (b) are diagrams illustrating the mold layout when forming the belt-side paper guide 36 according to this embodiment by injection molding, and the mold layout when forming the belt-side paper guide 536 (Figure 11) according to the prior art by injection molding.

Note that Figures 7(a) and (b) show the mold and molded part, the paper guide, before demolding (before the mold is removed and the molded part is taken out) in a cross section perpendicular to the X-axis direction (see Figures 2 and 11), but for simplicity, the cross section of the mold is not hatched.

Figure 7(b) is a cross-sectional view illustrating the mold used in injection molding of a conventional belt-side paper guide.

As shown in the figure, a conventional mold consists of three split molds 421-423, and when demolding, each split mold is opened in the directions of arrows K11-K13, respectively, along mold parting lines 424-426.

For ease of mold release, the mold parting line 425 (the joint between the split molds 421 and 423) is located at the angle 5362a at the tip of the rib 5362 of the paper guide 536, and as a result, small steps and burrs may occur in this area.

The inventors of this application have discovered that when the fixing belt floats and comes into contact with the tip 5362a of the rib 5362, these tiny steps and burrs make the surface of the fixing belt 31 even more susceptible to damage.

In this embodiment, as described above, a belt protection member is provided to prevent scratches on the fixing belt 31. However, if there are any steps or burrs remaining on the tip of this belt protection member (the end on the nip portion Np side), there is still a risk of scratches on the fixing belt, although these may be smaller than in the past.

It is possible to remove steps and burrs by polishing, but this requires additional labor and is not desirable from a cost perspective. Therefore, in this embodiment, the mold configuration has been devised.

Figure 7(a) is a cross-sectional view illustrating the mold used for injection molding the belt-side paper guide according to this embodiment.

As shown in the figure, the mold in this embodiment consists of three split molds 411-413, and when demolding, each split mold is opened in the directions of arrows K1-K3, respectively, along mold parting lines 414-416.

A distinctive feature is that the die parting line 415 between the split dies 411 and 413 has been moved to the left end of the opposing surface 3632 of the belt protection member 363 of the belt-side paper guide 36.

As a result, even if tiny steps or burrs remain at the mold parting line 415 after demolding, by setting the inclination of the belt protection member 363 so that the distance G2 between the most downstream side of the opposing surface 3632 of the belt protection member 363 in the running direction of the fixing belt 31 (i.e., the side farthest from the nip portion Np) and the fixing belt 31 is greater than the distance G1 between the most upstream side of the opposing surface 3632 of the belt protection member 363 in the running direction of the fixing belt 31 (i.e., the side closest to the nip portion Np) and the fixing belt 31, as shown in Figure 8, even if belt lift occurs, the fixing belt 31 is less likely to come into contact with the steps and burrs at the most downstream side of the belt protection member 363 in the running direction of the fixing belt 31, which can further contribute to preventing scratches on the fixing belt 31.

As explained above, according to this embodiment, even if belt behavior becomes unstable due to fluctuations in rotational torque or the like, causing the belt to float, by providing a belt protection member at a position closer to the nip portion Np than the tip of the rib on the nip portion Np side, it is possible to reduce manufacturing costs with a simple configuration and prevent damage to the fixing belt, thereby providing an image forming apparatus equipped with a fixing device that consistently satisfies good fixing quality over a long period of time.

When manufacturing the belt-side paper guide by injection molding, in addition to using the belt protection member, by devising a mold split when molding the belt-side paper guide, it is possible to reduce manufacturing costs and more effectively prevent scratches on the fixing belt.

<Modification>
The above has been described based on the embodiments of the present disclosure, but it goes without saying that the present disclosure is not limited to the above-described embodiments, and the following modifications are possible.

(1) In the fixing unit 30 according to the above embodiment, the fixing belt 31 is sandwiched between the fixing pad 33 and the pressure roller 32 to form a nip portion (hereinafter, the member that sandwiches the fixing belt 31 to form the nip portion is referred to as the "nip portion forming member").

However, in such a nip-forming member, a fixing roller may be used as the support instead of the fixing pad 33. Even in this case, the same belt lifting phenomenon that occurs when the fixing pad 33 is used can cause scratches on the surface of the fixing belt 31.

In this case, to save energy, it is desirable for the fixing roller to be hollow and made of a resin material with as high an insulating property as possible and with as little heat capacity as possible.

(2) In the above embodiment, as shown in Figures 3, 5, and 6, the belt-side paper guide 36 is provided with a belt protection member wider than the rib 362 along the lower edge 3611 at the tip of the rib 362, thereby increasing the contact area with the floating portion of the fixing belt 31 and protecting the fixing belt 31 from damage. However, by widening the width of the rib 362 itself in the X direction and increasing the area of the lower end face of the rib 362 itself, it is also possible to increase the contact area with the floating portion of the fixing belt 31 and prevent damage to the fixing belt 31.

Figure 9(a) is a perspective view of the belt-side paper guide 36 in such a case, and Figure 9(b) is an enlarged view of the area surrounded by dashed line J4 in Figure 9(a).

In this modified example, two types of ribs 366, 367 are formed with widths W1 and W2 (W1 > W2) in the X direction that are larger than conventional ribs. To ensure smooth transport of the recording sheet S, the arrangement of the ribs 366, 367 in the X direction is symmetrical with respect to the paper passing center M.

To avoid damaging the fixing belt 31, it is desirable that W2 ≥ 6 mm. Furthermore, if the width of the rib 366 is too large, contact friction with the recording sheet S increases and toner immediately after fixing tends to adhere to the top surface of the rib, so it is desirable that W1 ≤ 11 mm.

In this modified example, the height of each rib is set to, for example, 2 mm, but this is not limited to this and may be determined appropriately to obtain the required contact area.

Furthermore, the width of rib 366 does not necessarily have to be greater than the width of rib 367 (W1 > W2); even if they have the same width (W1 = W2), it is sufficient as long as the upper and lower limits are within the above range (6 mm or more and 11 mm or less).

Furthermore, each rib does not necessarily have to have the same width over the entire length of the recording sheet S in the transport direction; for example, it may have a shape that gradually narrows from the tip on the nip side toward the downstream side in the sheet transport direction. In this case, it is sufficient that the width at least at the tip on the nip side is within the above range.

(3) In the above embodiment, for example, in Figure 3, the belt protection member 363 is formed integrally with the tip of the rib 362, but this is not necessarily required. Even if the belt protection member 363 is separate from the rib 362 and is located closer to the nip portion Np than the tip of the rib 362 on the nip portion Np side and in close proximity to that tip (for example, approximately 1 mm to 2 mm away), there will be no interference with guiding the recording sheet S as long as the tip of the recording sheet S scooped up by the belt protection member 363 does not abut against the end surface of the tip of the rib 362.

(4) In the above embodiment, the fixing unit 30 uses a heating roller 34 with a built-in halogen heater as the heat source. However, this is not limiting and the fixing belt 31 may be heated by electromagnetic induction, or the fixing device may be configured to directly pass electricity through the fixing belt 31 to generate resistance heat.

(5) In the above embodiment, an embodiment of a fixing unit was described as one aspect of the disclosed sheet conveying device, but it can also be applied to the secondary transfer unit in the image forming unit 20 (Figure 1).

Figure 10 shows an example of the configuration of the secondary transfer unit (transfer device) according to this modified example. Components that are the same as those in Figure 1 are assigned the same reference numerals, and therefore their explanation will be omitted.

As shown in the figure, a secondary transfer roller 24 is disposed opposite the drive roller 23R, with an endless intermediate transfer belt (image-carrying belt) 23 interposed between them, and a transfer nip TN is formed between the intermediate transfer belt 23 and the secondary transfer roller 24.

After passing through the transfer nip TN, the recording sheet S is guided by a pair of sheet guides 290, 294 and transported further upward.

Due to the influence of the toner, the recording sheet S adheres to the intermediate transfer belt 23 and continues to be transported even after passing through the transfer nip TN. When the leading edge of the recording sheet S is lifted due to its stiffness, it is picked up by the lower end of the sheet guide 290 and guided upward.

When the device is started up, for example, and the intermediate transfer belt 23 begins to rotate, the rotational torque becomes unstable due to friction between the cleaning blade 23B and the intermediate transfer belt 23 (static friction is greater than dynamic friction, and friction is greater at this point because there is not much toner remaining on the surface of the intermediate transfer belt 23 as a lubricant), making the intermediate transfer belt 23 prone to lifting.

For this reason, similar to the belt-side paper guide 36 in the fixing unit 30, a belt protection member 293 having a shape similar to the belt protection member 363 in the above-described embodiment is provided at the tip of the nip portion Np of the rib 292 provided on the sheet guide surface side of the guide body 291 of the sheet guide 290, to prevent scratches on the surface of the intermediate transfer belt 23 even when it comes into contact with the intermediate transfer belt 23.

This prevents deterioration of the intermediate transfer belt 23 and prevents a decrease in the image quality of the transferred toner image.

In addition, in image forming devices that use a photosensitive belt instead of an intermediate transfer belt, form a toner image directly on the photosensitive belt, and then transfer it to a recording sheet S, the photosensitive belt serves as the image bearing belt.

(6) The sheet conveying device according to the present disclosure is not limited to the fixing device or transfer device described above, but can be applied to any sheet conveying device that forms a nip using an endless belt and a rotating body and conveys any sheet, not limited to recording sheets, through the nip, and is equipped with a guide member that guides a sheet discharged from the nip along the endless belt, as well as to image forming apparatuses equipped with such a sheet conveying device.

<Additional Information>
The fixing device, transfer device, and image forming apparatus equipped with the sheet conveying device according to the present disclosure have been described above based on the embodiments and modifications, but the present invention is not limited to the above embodiments and modifications. The present invention also includes forms obtained by applying various modifications to the above embodiments and modifications that would occur to those skilled in the art, and forms realized by arbitrarily combining the components and functions of the embodiments and modifications within the scope of the present invention.

This disclosure can be widely applied to image forming devices that include belt-type fixing devices that thermally fix unfixed toner images formed on a sheet using a fixing belt, and transfer devices that transfer toner images on an intermediate transfer belt onto a sheet.

REFERENCE SIGNS LIST 1 Printer 20 Imaging unit 23 Intermediate transfer belt 23L Driven roller 23R Drive roller 23B Cleaning blade 24 Secondary transfer roller 30 Fixing unit 31 Fixing belt 31a Belt float 32 Pressure roller 33 Fixing pad 34 Heating roller 36 Belt-side paper guide 361 Guide body 362, 367, 368 Ribs 363 to 365 Belt protection member

Claims (9)

A sheet conveying device that forms a nip portion by pressing an endless belt between a long support body and a rotating body, and conveys a sheet by passing it through the nip portion,
a guide member for guiding the sheet discharged from the nip portion toward the endless belt,
The guide member has a plurality of ribs extending along the sheet conveying direction and arranged in parallel in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide body,
a belt protection member having a height at least equal to the tip ends of the ribs and a width greater than the tip ends is provided along an edge of the guide body on the nip side,
The rib has a first portion on the upstream side and a second portion on the downstream side, and when viewed from the side, the ridge of the top of the first portion that contacts the sheet is shaped to retreat in a direction away from the sheet conveying path as it moves upstream from the boundary with the second portion to the tip portion on the nip side. The sheet conveying device according to claim 1 , wherein the belt protection member is formed as a single continuous member along an edge of the guide body on the nip side. A sheet conveying device that forms a nip portion by pressing an endless belt between a long support body and a rotating body, and conveys a sheet by passing it through the nip portion,
a guide member for guiding the sheet discharged from the nip portion toward the endless belt,
The guide member has a plurality of ribs extending along the sheet conveying direction and arranged in parallel in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide body,
a belt protection member having a height at least equal to the tip ends of the ribs and a width greater than the tip ends is provided along the edge of the guide body on the nip side at a position closer to the nip portion than the tip ends of the plurality of ribs,
The sheet conveying device, wherein the belt protection member is divided into a plurality of parts and provided along an edge of the guide body on the nip side. The sheet conveying device of claim 3, characterized in that the tip of the rib and the belt protection member are formed integrally, and the tip of the rib on the nip side is connected to the belt protection member to form a T-shape and/or the tip of the nip side of two adjacent ribs is connected to each other via the belt protection member to form a U-shape. A sheet conveying device that forms a nip portion by pressing an endless belt between a long support body and a rotating body, and conveys a sheet by passing it through the nip portion,
a guide member for guiding the sheet discharged from the nip portion toward the endless belt,
The guide member has a plurality of ribs extending along the sheet conveying direction and arranged in parallel in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide body,
a belt protection member having a height at least equal to the tip ends of the ribs and a width greater than the tip ends is provided along the edge of the guide body on the nip side at a position closer to the nip portion than the tip ends of the plurality of ribs,
a belt protection member disposed so that, when there is no floating in the endless belt, the distance between the surface of the belt protection member facing the endless belt and the surface of the endless belt is greater at a second position on the facing surface that is farthest from the nip portion than at a first position on the facing surface that is closest to the nip portion. The guide member is made of a resin material .
6. The sheet transport device according to claim 5. A sheet conveying device that forms a nip portion by pressing an endless belt between a long support body and a rotating body, and conveys a sheet by passing it through the nip portion,
a guide member for guiding the sheet discharged from the nip portion toward the endless belt,
The guide member has a plurality of ribs extending along the sheet conveying direction and arranged in parallel in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide body,
a width of the tip ends of the plurality of ribs on the nip side in a direction perpendicular to the sheet conveying direction is 6 mm or more and 11 mm or less. A sheet conveying device that forms a nip portion by pressing an endless belt between a long support body and a rotating body, and conveys a sheet by passing it through the nip portion,
a guide member for guiding the sheet discharged from the nip portion toward the endless belt,
The guide member has a plurality of ribs extending along the sheet conveying direction and arranged in parallel in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of the guide body,
a belt protection member having a height at least equal to the tip ends of the ribs and a width greater than the tip ends is provided along the edge of the guide body on the nip side at a position closer to the nip portion than the tip ends of the plurality of ribs,
A sheet conveying device characterized in that the endless belt is an image carrying belt that carries a toner image, and the rotating body is a transfer roller that transfers the toner image carried on the surface of the image carrying belt onto a sheet that passes through a nip portion between the image carrying belt and the rotating body. An image forming apparatus comprising the sheet conveying device according to any one of claims 1 to 8 .