Sheet conveying device and image forming apparatus

Abstract

To provide a sheet conveying device using an endless belt, and even when floating of the endless belt occurs, prevent occurrence of scratches due to contact with a paper feed guide.SOLUTION: A sheet conveying device brings a long-sized support and a rotating body into pressure contact with each other and sandwiches an endless belt therebetween to form a nip part, and feeds a sheet to the nip part to convey the sheet, and the sheet conveying device comprises a belt-side paper feed guide 36 that is on a downstream side of the nip part in a sheet feeding direction and guides the sheet ejected from the nip part closer to the endless belt. The belt-side paper feed guide 36 is formed by providing, on the side of a sheet guide surface, a plurality of ribs 362 extending along a sheet conveyance direction in parallel in a direction orthogonal to the sheet conveyance direction. At tips on a nip side of the plurality of ribs 362, belt protection members 363 having at least a same height as the tips of the ribs and a wider width than the tips of the ribs are disposed along an edge 3611 on the nip side of the belt-side paper feed guide 36.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a sheet conveying device having an endless belt and an image forming apparatus having the sheet conveying device. [Background technology]

[0002] An electrophotographic image forming apparatus includes a fixing device that thermally fixes a sheet on which an unfixed toner image has been formed by passing the sheet through a nip formed between a heating rotor and a pressure rotor.

[0003] In recent years, from the viewpoint of energy conservation, belt-type fixing devices have been widely adopted in which a fixing belt (endless belt) is stretched between a heating roller, which is 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 portion.

[0004] The fixing belt is formed primarily from metal or resin materials, is relatively thin, and has a small heat capacity, which reduces the time it takes to heat up to the fixing temperature when the device is started up or from standby mode, thereby contributing to energy savings.

[0005] 11 is a cross-sectional view showing an example of the configuration of a conventional fixing device using 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 inside a housing 538 of the fixing device.

[0006] The fixing belt 531 is stretched between a fixing pad 533 and a heating roller 534, and a portion of the fixing belt 531 corresponding to the fixing pad 533 is pressed by a pressure roller 532 to form a nip portion Np.

[0007] The pressure roller 532 is driven to rotate in the direction of arrow Q by a drive source (not shown), and the fixing belt 531 moves in the direction of arrow P in response to the pressure roller 532, and the heating roller 534 also rotates in response to the fixing belt 531.

[0008] A heater 535 is built in the heating roller 534, and heats the fixing belt 531. A recording sheet on which an unfixed toner image has been formed is passed through the nip portion Np and is thermally fixed.

[0009] Downstream of the nip portion Np in the paper passing direction (from bottom to top in Figure 11), a pair of paper passing guides 536, 537 are arranged to guide the sheet that has passed through the nip portion Np toward an outlet 539 of the housing 538 of the fixing device.

[0010] FIG. 12A is a perspective view of the paper passing guide 536 as seen from a position slightly to the right of FIG.

[0011] As shown in the same figure, the paper passage guide 536 has a long, plate-shaped guide body 5361 extending in the width direction (direction perpendicular to the running direction) of the fixing belt 531, and has multiple ribs 5362 erected on the surface facing the sheet, parallel to the sheet passage direction.

[0012] FIG. 12(b) is an enlarged view of the portion surrounded by the semicircular dashed line J5 in FIG.

[0013] Rib 5362 is provided to reduce the contact area with the sheet and guide the sheet toward the discharge outlet of housing 538, so it is designed to have a narrow width W11 of about 1 mm and a height H11 of about 2 mm.

[0014] 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 tension at a position where it separates from the fixing belt 531 and guides the sheet upward. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-93582 Summary of the Invention [Problem to be solved by the invention]

[0016] However, when rotating the fixing belt 531, particularly when turning on the image forming apparatus and starting it 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, due to factors such as static friction at the bearing portion of the heating roller 534, the rotational torque becomes unstable and the behavior of the fixing belt 531 also becomes unstable, which may 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").

[0017] If even a slight amount of belt lift occurs, the fixing belt 531 comes into contact with the lower end (the end on the nip portion Np side) of the paper passing guide 536 disposed close to the fixing belt 531.

[0018] As described above, the width W11 of the rib 5362 is not particularly large, so when the fixing belt 531 comes into contact with the lower end of the rib 5362, particularly the corner 5362a (FIG. 12(b)), many fine scratches 531b are generated on the surface of the fixing belt 531, as shown in FIG. 12(c), which causes problems such as gloss streaks in the fixed image and degradation of image quality.

[0019] 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 drive roller is rotated so that its peripheral speed is faster than that of the fixing belt, thereby applying tension to the fixing belt in a direction that eliminates belt lift, thereby suppressing belt lift.

[0020] However, if a separate drive roller is provided as in Patent Document 1, the device becomes larger, the number of parts increases, and the manufacturing cost increases.

[0021] The problem of preventing belt deterioration due to contact with the ribs of the paper-passing guide 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-passing guide is arranged close to the endless belt downstream of the nip.

[0022] The present disclosure has been made in consideration of the above circumstances, and aims to provide a sheet conveying device having 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 device equipped with such a sheet conveying device. [Means for solving the problem]

[0023] In order to achieve the above object, a sheet conveying device according to one 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 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 in a direction perpendicular to the sheet conveying direction on the sheet guide surface side of a guide body, and the tips of the plurality of ribs on the nip side To the department A belt protection member having a height at least equal to that of the tip end of the rib and a width greater than that of the tip end is provided along the 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 in a side view, a ridge line of the top of the first portion that contacts the sheet is shaped to recede in a direction away from the sheet conveying path as it moves from the boundary with the second portion to the tip portion on the nip side on the upstream side. It is characterized by:

[0024] In another 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.

[0025] In addition, the present disclosure Another One aspect The sheet transport device according to claim 1 is a sheet transport 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 transported, and the sheet transport device 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 transport direction and are arranged side by side in a direction perpendicular to the sheet transport 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 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 belt protection member is divided into a plurality of parts and provided along the edge of the guide body on the nip side.

[0026] In addition, in one embodiment 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.

[0027] In addition, the present disclosure Another One aspect The sheet transport device according to claim 1 is a sheet transport 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 transported, and the sheet transport device 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 transport direction and are arranged side by side in a direction perpendicular to the sheet transport 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 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 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 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.

[0028] In addition, in one aspect of the present disclosure, the guide member is Resin materials formed by It is something .

[0029] Another aspect of the present disclosure is a sheet conveying device that forms a nip by pressing an endless belt between a long support body and a rotating body, and conveys a sheet by passing it through the nip, and is equipped with a guide member that guides a sheet that has been discharged from the nip toward the endless belt, and the guide member has multiple ribs that extend along the sheet conveying direction and are arranged in a direction perpendicular to the sheet conveying 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 conveying direction is 6 mm or more and 11 mm or less.

[0030] In addition, the present disclosure Another One aspect The sheet transport device according to claim 1 is a sheet transport 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 transported, and the sheet transport device 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 transport direction and are arranged side by side in a direction perpendicular to the sheet transport 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 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 endless belt is a fixing belt, and a heating means for heating the fixing belt is provided.

[0031] In addition, the present disclosure Another One aspect The sheet transport device according to claim 1 is a sheet transport 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 transported, and the sheet transport device 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 transport direction and are arranged side by side in a direction perpendicular to the sheet transport 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 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 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 passes through the nip between the image carrying belt and the rotating body.

[0032] Another aspect of the present disclosure is an image forming apparatus including the sheet conveying device described above. [Effects of the Invention]

[0033] According to the configuration of the sheet conveying device of the above-disclosed aspect, even if the endless belt floats, the belt protection member has a larger contact area with the endless belt than the end face of the lower end of the rib of a conventional paper passing guide, so the surface of the endless belt is less likely to be damaged. Also, 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 the cost burden is low. [Brief explanation of the drawings]

[0034] [Figure 1] 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. [Figure 2] FIG. 2 is a cross-sectional view illustrating a configuration of a fixing unit of the printer. [Figure 3] 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. [Figure 4] 10A and 10B are diagrams for explaining the effects of the belt-side paper guide. [Figure 5] 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. [Figure 6] 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. [Figure 7]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. [Figure 8] 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. [Figure 9] 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. [Figure 10] 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. [Figure 11] 1A and 1B are diagrams for explaining problems with a conventional belt-type fixing device. [Figure 12] 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. DETAILED DESCRIPTION OF THE INVENTION

[0035] Below, we will explain, 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 image forming apparatus having the fixing device.

[0036] (1) Overall configuration of the printer FIG. 1 is a schematic cross-sectional view showing the overall configuration of the printer 1.

[0037] As shown in the figure, the printer 1 is an electrophotographic printer and includes a feeding section 10, an image creating section 20, a fixing section 30, an ejection section 40, and a double-sided conveying section 50, and is capable of executing a single-sided print job in which an image is printed on only one side (front side) of a recording sheet S for recording, and a double-sided print job in which an image is printed on both sides (front and back sides) of the recording sheet S.

[0038] The feeding section 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 a conveying path 19, a paper feed roller 12F that feeds and conveys 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.

[0039] The image creating unit 20 forms a toner image on the recording sheet S sent from the feeding unit 10. Specifically, the four image creating units 21Y, 21M, 21C, and 21K expose the surfaces of the charged photosensitive drums 25Y, 25M, 25C, and 25K to laser light from an exposure unit 26 that is modulated and driven based on image data, creating an electrostatic latent image on the surface, and developing the electrostatic latent image with toner of each color: yellow (Y), magenta (M), cyan (C), and black (K).

[0040] The four-color toner images visualized by development are primarily transferred from the surfaces of the photosensitive drums 25Y, 25M, 25C, and 25K to the surface of the intermediate transfer belt 23 by an electric field between the photosensitive drums 25Y, 25M, 25C, and 25K and primary transfer rollers 22Y, 22M, 22C, and 22K that face the photosensitive drums with the intermediate transfer belt 23 in between. In this primary transfer, the timing of forming the toner images in the imaging units 21Y to 21K is shifted so that the Y to K toner images are transferred to the same position on the intermediate transfer belt 23. As a result, a color toner image is formed on the intermediate transfer belt 23 by multiple transfer of the Y to K toner images.

[0041] Intermediate transfer belt 23 is positioned above photosensitive drums 25Y to 25K, is 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, which is the contact position between intermediate transfer belt 23 and secondary transfer roller 24. Secondary transfer roller 24 is urged toward intermediate transfer belt 23 by a urging means (not shown), and a predetermined nip pressure is generated between them.

[0042] At secondary transfer position 29, the color toner image on intermediate transfer belt 23 is secondarily transferred to the surface (first surface) of recording sheet S by the electric field between intermediate transfer belt 23 and secondary transfer roller 24 when recording sheet S conveyed from feeder 10 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.

[0043] The recording sheet S onto which the color toner image (unfixed image) has been secondarily transferred is conveyed by the secondary transfer roller 24 in the direction of arrow E toward the fixing unit 30.

[0044] The fixing unit 30 includes a fixing belt (endless belt) 31 and a pressure roller (rotating body) 32, and the color toner image is thermally fixed onto the recording sheet S by passing the recording sheet S through the nip portion Np formed between the two.

[0045] The discharge section 40 includes a discharge roller 41 and a paper discharge port 45, and discharges the recording sheet S on which the color toner image has been fixed from the paper discharge port 45. The discharge roller 41 is arranged inside the paper discharge port 45, and while rotating in the direction of arrow B (forward rotation), it transports the recording sheet S transported from the fixing section 30 from the paper discharge port 45 and discharges it outside the machine. The discharged paper S is stored in a paper discharge tray 46. This completes single-sided printing, in which printing is done only on the first side of the recording sheet S.

[0046] Furthermore, 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 in the transport direction 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).

[0047] As a result of this reversal of the discharge roller 41, the recording sheet S is inverted and guided to the double-sided conveying section 50, where it is conveyed 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 conveyed again to the secondary transfer position 29 via the timing roller 13, where 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 to the paper output tray 46 via the discharge roller 41.

[0048] In the feed unit 10 and the 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 a drive motor M1 arranged in the imaging unit 20. In addition, the pressure roller 32 in the fixing unit 30 is driven to rotate by a drive motor (fixing motor) M2, the discharge roller 41 rotates forward and reverse by the driving force of a drive motor M3 arranged in the discharge unit 40, and the duplex transport rollers 51-55 are rotated by the driving force of a drive motor M4 arranged in the duplex transport unit 50.

[0049] The control unit 100 is also connected to an external terminal device via a network, receives print job data sent from the terminal device, generates image data to be printed from the received print job data, and provides the generated image data for printing.

[0050] (2) Configuration of the fixing unit FIG. 2 is a cross-sectional view showing the configuration of the fixing unit 30. As shown in FIG.

[0051] 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.

[0052] In FIG. 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).

[0053] 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.

[0054] The surface of the fixing pad 33 that comes into contact with the fixing belt 31 is preferably subjected to a surface treatment and / or coated with a lubricant to reduce friction.

[0055] The fixing belt 31 is formed by laminating, in this order, a base layer made of, for example, polyimide or SUS (stainless steel), 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.

[0056] 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 circumferential surface of a cylindrical core metal 321 made of aluminum, iron, etc. A release layer (not shown) made of PFA or the like may be further laminated on the outermost layer.

[0057] The pressure roller 32 is pressed against the outer circumferential surface of the fixing belt 31 with a predetermined load (pressure contact force) by the biasing force of an elastic member (not shown) such as a spring. This pressure contact forms a nip Np between the outer circumferential surface of the pressure roller 32 and the outer circumferential surface of the fixing belt 31.

[0058] Pressure roller 32 functions as a drive roller, being rotated at a predetermined rotation speed in the direction of arrow Q by the rotational drive force of fixing motor M2 (FIG. 1). The rotation of pressure roller 32 causes heating roller 34 and fixing belt 31, which is stretched between heating roller 34 and fixing pad 33, to rotate (run) in the direction of arrow P.

[0059] The heating roller 34 is, for example, formed by laminating a coating layer made of PTFE (polytetrafluoroethylene) on the outer surface of a cylindrical aluminum hollow core, and both axial ends thereof are rotatably supported by the frame of the housing 38 of the fixing unit 30.

[0060] A heater section 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 range of the heating roller 34 in the axial direction (longitudinal direction: X-axis direction in Figure 2) and a second heater 3412 that heats the central part in the axial direction, and generates heat when power is supplied from a power source not shown, thereby heating the heating roller 34.

[0061] The heating roller 34 is held in an elongated hole (not shown) in the frame of the housing 38 via a bearing member 342. The long diameter of the elongated hole is inclined diagonally to the right in the figure, and by urging the bearing member 342 diagonally downward to the left by an elastic member 343 such as a compression spring, the heating roller 34 is urged in a direction away from the fixing pad 33, and a predetermined amount of tension is applied to the fixing belt 31.

[0062] When the heater section 341 is energized while the fixing belt 31 is rotating, heat generated from the heater section 341 is transferred from the heating roller 34 to the fixing belt 31, and reaches the nip portion Np as the fixing belt 31 rotates.

[0063] As a result, heat from the fixing belt 31 is supplied to the pressure roller 32 and the fixing pad 33, and the temperature of the nip portion Np, which is the contact area between the fixing belt 31 and the pressure roller 32, rises.

[0064] A temperature sensor (not shown) is arranged near the part of the fixing belt 31 that comes into contact with the outer surface of the heating roller 34, and detects the surface temperature of the fixing belt 31. Based on the detection result, the control unit 100 turns on and off the power supplied to the heater unit 341 to control the fixing belt 31 to reach the target temperature.

[0065] The recording sheet onto which the toner image has been transferred passes through the nip portion Np with the surface onto which the toner image has been transferred 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 onto the recording sheet.

[0066] A pair of paper guide members 391 and 392 on the entrance side are arranged upstream of the nip portion Np in the sheet conveying direction, and guide the recording sheet S that has passed through the secondary transfer position 29 toward the nip portion Np.

[0067] 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.

[0068] The recording sheet S that has passed through the nip portion Np adheres to the surface of the fixing belt 31 due to the fused toner, and 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 portion Np has a large curvature, the leading edge of the recording sheet S lifts up from the surface of the fixing belt 31 due to the stiffness of the recording sheet S itself at that point, and the leading edge 3631 (see FIG. 4) on the nip portion Np side of the paper passing guide 36 on the fixing belt 31 side (hereinafter referred to as the "belt-side paper passing guide 36") is scooped up and guided upward (this scooping up of the leading edge of the recording sheet from the fixing belt by the belt-side paper passing guide is hereinafter referred to as the "scooping function").

[0069] To effectively utilize the scooping function, it is desirable to minimize the distance between the leading end 3631 of the belt-side paper guide 36 and the surface of the fixing belt 31 when the belt is stopped (when no belt lift occurs). Otherwise, thin sheets, in particular, have weak stiffness, so the leading end lifts only slightly, causing the sheet to be caught in the fixing belt 31 and causing problems. In this embodiment, the distance is set to approximately 1 to 2 mm, but is not limited to this and can be positioned as close as possible to the extent that the scooping function can be utilized depending on the specifications of the device (such as 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, and the material of the fixing belt 31).

[0070] However, when the fixing belt 31 is placed in such close proximity, if the fixing belt 31 is unstable, such as when the device is started up, the fixing belt 31 may float as described above and come into contact with the lower end of the rib of the belt-side paper guide.

[0071] As mentioned above, conventionally, the width of this rib was small and the corners of its lower end were relatively sharp and faced the fixing belt 31, which caused scratches on the surface of the fixing belt 31 and resulted 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, so that the surface of the fixing belt 31 will not be scratched even if the belt floats.

[0072] When a double-sided print job is executed, when a recording sheet S having 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 side, so in this embodiment, a separation claw 371 is provided on the paper passing guide 37 side.

[0073] (3) Belt protection member Three examples of the belt protection member in the belt-side paper guide according to this embodiment will be described below.

[0074] (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).

[0075] 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, and on the sheet guide surface side (the surface that guides the recording sheet S) of the guide body 361, multiple ribs 362 extending in the direction along the recording sheet S transport direction E (see Figure 1) are arranged in parallel in the longitudinal direction (X direction).

[0076] The ribs 362 are provided in a plurality of positions in the X direction for each of the sizes of recording sheets S usable in the printer 1, at positions necessary to guide at least the central periphery and both ends in the width direction.

[0077] In this embodiment, at a position closer to the nip portion Np than the lower end portion (tip portion on the nip portion Np side) of the rib 362, a belt protection member 363 is formed integrally with the rib 362 along the lower edge portion 3611 of the belt side paper guide 36, and is T-shaped when viewed upside down from the Y-axis direction.

[0078] In this embodiment, the height of the belt protection member 363 (height from the guide-side surface of the guide body 361) is set to be equal to the height of the lower end (tip 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 of the belt-side paper guide 36 within the housing 38, and the need to perform the function of scooping up the tip of the recording sheet S of the belt-side paper guide 36.

[0079] The width of the belt protection member 363 (width in the X-axis direction) is larger than the width of the lower end of the rib 362, and is preferably 5 mm or more.

[0080] If the width is at least wider than the width of the rib 362, the contact area with the fixing belt 31 when the belt lift occurs can be increased, and the occurrence of damage to the fixing belt 31 can be suppressed more than before.

[0081] 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 .

[0082] 4 is a diagram for explaining the effect of providing the belt protection member 363 to the belt-side paper-passing guide 36 in the fixing unit 30. For simplification, the paper-passing guide 37 and the like are omitted from the illustration.

[0083] As shown in FIG. 4, even if belt lift 31a occurs on the fixing belt 31 when starting up the printer 1, the fixing belt 31 comes into contact with 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, thereby suppressing scratches on the surface of the fixing belt 31 and preventing deterioration of the fixed image.

[0084] It is desirable that the positions of the multiple ribs 362 and the lengths of the belt protection members 363 in the X-axis direction are symmetrical with respect to the paper passing center (center in the X-axis direction) M (FIG. 3(a)) in the sheet conveying path. This is because the contact resistance with the recording sheet S is symmetrical across the paper passing center M in the sheet width direction, allowing the recording sheet S to be conveyed smoothly without skewing.

[0085] (3-2) Second Example of Belt Protection Member In the first embodiment, the belt protection member 363 is integrally formed 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.

[0086] Figure 5(a) is an oblique view of the belt-side paper guide 36 of the second embodiment when 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).

[0087] As shown in FIG. 5(a), a belt protection member 364 in this embodiment has a shape in which the plurality of belt protection members 363 in the first embodiment are connected together in the X direction to form a single member.

[0088] In this embodiment, the height of the belt protection member 364 is sufficient as long as it is at least as high as the lower end of the rib 362 .

[0089] According to this second embodiment, the area of ​​the opposing surface 3642 of the belt protection member 364 that faces the fixing belt 31 is increased, and the contact area with the belt floating portion 31a of the fixing belt 31 can be significantly increased compared to the first embodiment, thereby further enhancing the effect of preventing scratches on the fixing belt 31.

[0090] 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 the edge will be thick over almost the entire X-direction. Therefore, when manufacturing using injection molding, there is a risk of "warping" occurring in the X-axis direction due to variations in the cooling rate in the longitudinal direction.

[0091] The "warping" in the X direction may cause variations in the gap in the X direction between the lower edge of the belt-side paper-passing guide 36 and the fixing belt 31, which may prevent the belt 364 from fully performing its function of scooping up the leading edge of the recording sheet S and guiding it rearward. Therefore, when manufacturing the belt 364 by injection molding, it is desirable to determine the dimensions of the belt protection member 364 (height and width in the sheet conveying direction) taking into consideration the characteristics of the resin material used and the allowable range of variations in the gap to ensure the scooping function.

[0092] The belt protection member 364 does not necessarily have to be continuous across all of the ribs 362, but may be separated at appropriate locations excluding the locations where the tips of the ribs 362 are located.

[0093] (3-3) Third embodiment of belt protection member Figure 6(a) is a perspective view of the belt-side paper guide 36 of 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 dashed line J3 in Figure 6(a).

[0094] 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).

[0095] When the T-shaped belt protection member 363 (FIG. 3(b)) and the U-shaped belt protection member 365 are combined, it is desirable to arrange them symmetrically with respect to the paper passing center M. This is because the magnitude of contact friction between the belt protection member and the recording sheet S is also symmetrical, and it is thought that the recording sheet S can be guided more smoothly along the conveying direction than if they were arranged randomly.

[0096] (4) Manufacturing method of belt-side paper guide In this embodiment, the belt-side paper guide 36 is manufactured by injection molding from the viewpoint of manufacturing costs.

[0097] Injection molding involves heating and melting resin materials such as synthetic resin (plastic), injecting them into a mold, and then cooling them to form the shape. Injection molding is advantageous in terms of manufacturing costs, as it allows for the continuous mass production of parts with complex shapes.

[0098] Figures 7(a) and (b) are diagrams for explaining the mold layout when forming the belt-side paper-passing guide 36 of this embodiment by injection molding, and the mold layout when forming the belt-side paper-passing guide 536 (Figure 11) in the prior art by injection molding, respectively.

[0099] In both Figures 7(a) and (b), the mold and the molded part, the paper guide, are shown in a cross section perpendicular to the X-axis direction (see Figures 2 and 11) before demolding (before the mold is removed and the molded part is taken out), but for simplicity's sake, the cross section of the mold is not hatched.

[0100] FIG. 7(b) is a cross-sectional view illustrating a mold used in injection molding of a conventional belt-side paper-passing guide.

[0101] As shown in the figure, the conventional mold is composed of three split molds 421 to 423, and when releasing the mold, the split molds are opened in the directions of arrows K11 to K13, respectively, along mold parting lines 424 to 426.

[0102] From the viewpoint of mold releasability, mold parting line 425 (the joint between split molds 421 and 423) is arranged at angle 5362a at the tip of rib 5362 of paper passing guide 536, and therefore, small steps and burrs may occur in this area.

[0103] The inventors of the present application have found that when the fixing belt floats and comes into contact with the tip portion 5362a of the rib 5362, these minute steps and burrs make the surface of the fixing belt 31 even more susceptible to damage.

[0104] 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 at 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.

[0105] Although it is possible to remove the steps and burrs by polishing, this would require additional steps and is not desirable from the viewpoint of cost. Therefore, in this embodiment, the configuration of the mold is devised.

[0106] FIG. 7(a) is a cross-sectional view illustrating a mold used for injection molding the belt-side paper-passing guide according to this embodiment.

[0107] As shown in the figure, the mold in this embodiment consists of three split molds 411 to 413, and when releasing the mold, each split mold is opened in the directions of arrows K1 to K3, respectively, along mold parting lines 414 to 416.

[0108] A distinctive feature is that the die parting line 415 between the split dies 411 and 413 has been moved to the left end position of the opposing surface 3632 of the belt protection member 363 of the belt-side paper-passing guide 36.

[0109] 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 in the running direction of the fixing belt 31 (i.e., the side farthest from the nip portion Np) of the belt protection member 363 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 the belt floats, 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.

[0110] As described above, according to this embodiment, even if the behavior of the belt 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 suppress the occurrence of scratches on the fixing belt while suppressing the burden of manufacturing costs with a simple configuration, and it is possible to provide an image forming apparatus equipped with a fixing device that always satisfies good fixing quality over a long period of time.

[0111] Furthermore, when the belt-side paper guide is manufactured by injection molding, in addition to the above-mentioned 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.

[0112] <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.

[0113] (1) In the fixing section 30 according to the above embodiment, a nip portion is formed by sandwiching the fixing belt 31 between the fixing pad 33 and the pressure roller 32 (hereinafter, the member that sandwiches the fixing belt 31 to form the nip portion in this manner is referred to as the “nip portion forming member”).

[0114] However, in such a nip portion forming member, a fixing roller may be used as the support instead of the fixing pad 33. This is because, even in this case, the same belt lifting phenomenon as when the fixing pad 33 is used can cause scratches on the surface of the fixing belt 31.

[0115] In this case, the fixing roller is preferably hollow and made of a resin material with as high adiabaticity and as small a heat capacity as possible in order to save energy.

[0116] (2) In the above embodiment, as shown in Figures 3, 5, and 6, in the belt-side paper guide 36, a belt protection member wider than the rib 362 is provided at the tip of the rib 362 along the lower edge 3611, thereby increasing the contact area with the floating portion of the fixing belt 31 and protecting the fixing belt 31 from damage. However, by increasing 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 possible to increase the contact area with the floating portion of the fixing belt 31 and prevent damage to the fixing belt 31.

[0117] FIG. 9(a) is a perspective view of the belt-side sheet guide 36 in such a case, and FIG. 9(b) is an enlarged view of the part surrounded by the dashed line J4 in FIG. 9(a).

[0118] In this modified example, two types of ribs 366 and 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 and 367 in the X direction is symmetrical with respect to the paper passing center M.

[0119] It is desirable that W2≧6 mm to avoid damaging the fixing belt 31. Furthermore, if the width of the rib 366 is too large, the contact friction with the recording sheet S increases and the toner immediately after fixing tends to adhere to the top surface of the rib, so it is desirable that W1≦11 mm.

[0120] In this modified example, the height of each rib is set to, for example, 2 mm, but is not limited to this and may be determined appropriately to obtain the required contact area.

[0121] Furthermore, the width of rib 366 does not necessarily have to be larger than the width of rib 367 (W1>W2); they may have the same width (W1=W2) as long as the upper and lower limits are within the above range (6 mm or more and 11 mm or less).

[0122] Furthermore, each rib does not necessarily have to have the same width over the entire length in the conveyance direction of the recording sheet S. For example, the rib may have a shape that gradually narrows from the tip on the nip side toward the downstream side in the sheet conveyance direction. In this case, it is sufficient that the width at least at the tip on the nip side is within the above range.

[0123] (3) In the above embodiment, for example, in Fig. 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 provided separately from the rib 362 and closer to the nip portion Np side than the tip of the rib 362 on the nip portion Np side and in a position close to the tip (for example, a position about 1 mm to 2 mm away), as long as the tip of the recording sheet S scooped up by the belt protection member 363 does not abut against the end face of the tip of the rib 362, there is no problem in guiding the recording sheet S.

[0124] (4) In the above embodiment, the fixing unit 30 uses a heating roller 34 with a built-in halogen heater as a heat source. However, the present invention is not limited to this configuration and may be configured to heat the fixing belt 31 by electromagnetic induction, or may be configured to directly pass electricity through the fixing belt 31 to generate heat by resistance heating.

[0125] (5) In the above embodiment, the fixing unit has been described as one aspect of the disclosed sheet conveying device, but the present invention is also applicable to the secondary transfer unit in the image forming unit 20 (FIG. 1).

[0126] FIG. 10 is a diagram showing an example of the configuration of a secondary transfer section (transfer device) according to this modified example, and since the same reference numerals as in FIG. 1 denote the same members as in FIG. 1, the description thereof will be omitted.

[0127] As shown in the same figure, a secondary transfer roller 24 is arranged opposite the drive roller 23R, with an endless belt-like intermediate transfer belt (image carrying belt) 23 in between, and a transfer nip TN is formed between the intermediate transfer belt 23 and the secondary transfer roller 24.

[0128] The recording sheet S that has passed through the transfer nip TN is guided by a pair of sheet guides 290, 294 and conveyed further upward.

[0129] Due to the influence of the toner, the recording sheet S adheres to the intermediate transfer belt 23 and is transported even after passing through the transfer nip TN, and 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.

[0130] 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 at this point there is not much toner remaining on the surface of the intermediate transfer belt 23 as a lubricant, so friction is high), and the intermediate transfer belt 23 is prone to floating.

[0131] Therefore, similar to the belt side paper guide 36 in the fixing section 30, a belt protection member 293 having a shape similar to the belt protection member 363 in the above 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, so that the surface of the intermediate transfer belt 23 is not scratched even when it comes into contact with the intermediate transfer belt 23.

[0132] This prevents deterioration of the intermediate transfer belt 23 and prevents the quality of the transferred toner image from deteriorating.

[0133] In an image forming apparatus that uses a photosensitive belt instead of an intermediate transfer belt, forms a toner image directly on the photosensitive belt, and then transfers it to a recording sheet S, the photosensitive belt serves as the image bearing belt.

[0134] (6) The sheet conveying device according to the present disclosure is not limited to a fixing device or a transfer device as described above, but is generally a device that forms a nip portion using an endless belt and a rotating body, and conveys any sheet, not limited to a recording sheet, by passing it through the nip portion. It can be applied to all sheet conveying devices that are equipped with a guide member that guides a sheet that has been discharged from the nip portion along the endless belt, and to image forming devices equipped with such a sheet conveying device.

[0135] <Supplementary 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. [Industrial Applicability]

[0136] The present disclosure can be widely applied to image forming apparatuses having a belt-type fixing device that thermally fixes an unfixed toner image formed on a sheet using a fixing belt, or a transfer device that transfers a toner image on an intermediate transfer belt onto a sheet. [Explanation of symbols]

[0137] 1. Printer 20 Imaging section 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 363~365 Belt protection member

Claims

1. 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 in a side view, a ridge line of the top of the first portion that contacts the sheet is shaped to recede in a direction away from the sheet conveying path as it moves from the boundary with the second portion to the tip portion on the nip side on the upstream side. A sheet conveying device characterized by:

2. The belt protection member is formed as a single continuous member along the edge of the guide body on the nip side.

2. The sheet transport device according to claim 1.

3. 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 belt protection member is divided into a plurality of parts along the edge of the guide body on the nip side. A sheet conveying device characterized by:

4. 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 two adjacent ribs on the nip side are connected to each other via the belt protection member to form a U-shape.

4. The sheet transport device according to claim 3.

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 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 belt protection member is disposed such that, in a state where no floating occurs in the endless belt, the distance between the surface of the endless belt 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. A sheet conveying device characterized by:

6. The guide member is made of a resin material.

6. The sheet transport device according to claim 5.

7. 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, The width of the tip of each 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 characterized by:

8. 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 endless belt is an image bearing belt that bears a toner image, and the rotating body is a transfer roller that transfers the toner image carried on the surface of the image bearing belt onto a sheet that passes through a nip between the image bearing belt and the rotating body. A sheet conveying device characterized by:

9. The sheet conveying device according to any one of claims 1 to 8 is provided. An image forming apparatus characterized by:

Images