JP4541990B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to a configuration for conveying a sheet on which a toner image is fixed.

  Conventionally, in an image forming apparatus such as a printer, a facsimile, or a copying machine that forms an image by an electrostatic recording method or an electrophotographic recording method, a non-fixed toner image formed on a sheet as a recording body is heated and pressurized to form a sheet. A fixing unit for fixing the toner image is provided thereon.

  A sheet conveying device including a conveying roller and a discharge roller is provided for discharging the sheet on which the toner image is fixed by the fixing unit to the outside of the image forming apparatus.

  FIG. 6 is a schematic configuration diagram of an image forming apparatus including such a conventional fixing unit and a sheet conveying device. The image forming apparatus includes an image forming unit 102 including a sheet feeding unit 120 that feeds a sheet P, and an image forming unit 101 (101a to 101d) that forms toner images of yellow, magenta, cyan, and black colors. I have.

  Further, a sheet conveying unit 130 that conveys the sheet P fed from the sheet feeding unit 120 to the image forming unit 102 to transfer each color toner image, and a fixing unit that fixes an unfixed toner image formed on the sheet P. 140. Reference numeral 151 denotes a paper discharge tray for collecting the sheets P discharged from the fixing unit 140.

  Here, as shown in FIG. 7, the fixing unit 140 receives a fixing roller pair including a pressure roller 142 and a heating roller 141 in which a heat source 146 is disposed, and a sheet P after fixing a sheet discharge tray. 151 is provided with a pair of discharge rollers 147 for discharging to 151. Further, conveyance guides 148 a and 148 b for guiding the sheet P that has passed through the fixing roller pair 141 and 142 to the paper discharge roller pair 147 are provided.

  By the way, when the sheet is discharged after fixing the toner image on the sheet, it is desirable that the sheet conveyance speed of the fixing roller pair 141 and 142 and the sheet conveyance speed of the paper discharge roller pair 147 are equal. However, there is a speed difference between the two roller pairs due to the influence of the accuracy of the parts and the discharge roller pair 147 expanding due to the heat of fixing heat.

  At this time, if the sheet conveyance speed of the discharge roller pair 147 is slower than the sheet conveyance speed of the fixing roller pair 141, 142, as shown in FIG. 8, the fixing roller pair 141, 142 and the discharge roller pair 147 The sheet P is slackened between the two, and the output sheet P is wrinkled. Furthermore, if the sag increases, eventually the sheet P cannot be normally conveyed to the paper discharge tray 151 and a paper jam occurs.

  Therefore, conventionally, the sheet conveyance speed of the discharge roller pair 147 is set to be always higher than the sheet conveyance speed of the fixing roller pairs 141 and 142. Note that the difference in sheet conveyance speed in this case is absorbed by slipping the sheet P by the discharge roller pair 147.

  However, when such a sheet conveyance speed difference is provided, the sheet P is pulled between the paper discharge roller pair 147 and the fixing roller pairs 141 and 142, and the conveyance guide 148b is bent as shown in FIG. It rubs at the bending point A. The rubbing surface of the sheet P is an image forming surface. If the image forming surface is rubbed, a serious image defect occurs.

  In order to prevent such rubbing of the image forming surface, for example, the conveyance guides 148a and 148b may be arranged linearly from the fixing roller pair 141 and 142 to the paper discharge roller pair 147 without bending. However, when the conveyance guides 148a and 148b are arranged linearly in this way, the position of the paper discharge roller pair 147 becomes a high position, which hinders downsizing and low cost of the image forming apparatus.

  Therefore, conventionally, a conveyance auxiliary roller is added between the fixing roller pair 141, 142 and the paper discharge roller pair 147 at a bent portion of the lower conveyance guide 148b (see, for example, Patent Document 1).

  By providing the conveyance auxiliary roller at the bent portion of the lower conveyance guide 148b in this way, even if the sheet P is pulled, the conveyance auxiliary roller is driven to rotate by the sheet P, so that the image forming surface is moved to the conveyance guide 148b. It can be prevented from being rubbed. As a result, it is possible to achieve good sheet conveyance in the fixing device without causing image defects, without causing a paper jam, and without causing an increase in the size and cost of the device.

JP 09-114153 A

  By the way, in the conventional fixing means in which the conveyance auxiliary roller is provided at the bent portion of the conveyance guide in this way, the conveyance auxiliary roller 143 is perpendicular to the sheet discharge direction on the lower conveyance guide 148b as shown in FIG. A plurality of them are provided in the axial direction that is the direction in which they are to be performed. Here, the conveyance auxiliary roller 143 includes a cylindrical roller body 145 and a support shaft 144 that rotatably holds the roller body 145.

  However, the sheet P discharged from the fixing nip N of the pair of fixing rollers 141 and 142 is in a direction perpendicular to the sheet discharging direction as shown in FIG. It may curl upward (U-shaped). Further, as shown in FIG. 9B, there is a case where it curls downward (inverted U shape).

  In this case, since only a part of the curled sheet P is in contact with the plurality of conveyance auxiliary rollers 43 arranged in the axial direction, the driven rotation by the sheet P cannot be performed or only insufficient rotation can be performed. In some cases, the surface of the roller body rubs the sheet P. As a result, a roller trace that is a rubbing trace is generated on the image.

  Accordingly, the present invention has been made in view of such a current situation, and even when a sheet on which a toner image is fixed by a fixing unit is curled, a sheet conveying apparatus and an image forming apparatus that can prevent the occurrence of a roller trace. The object is to provide an apparatus.

The present invention provides a sheet conveying apparatus for conveying a sheet on which the toner image is fixed by the fixing means, a guide member for guiding the sheet on which the toner image is fixed to the sheet over preparative discharge direction by said fixing means, said guide member A rotating body having a cylindrical shape that is arranged side by side in a direction orthogonal to the sheet discharge direction, is rotated by the sheet on which the toner image is fixed, and is in contact with the toner image fixing surface of the sheet, and the rotating body is rotated. And a plurality of driven rotating members that can be tilted with respect to the support shaft. The rotating shaft of the driven rotating member is inserted with the support shaft. An insertion portion, a holding portion that is provided at an inner central portion of the insertion portion, the support shaft is loosely fitted, a sponge layer that is arranged around the holding portion, and a sponge layer that is arranged around the sponge layer Chu And it is characterized in that it comprises Jo of the fluorine-based resin film, a.

  According to the present invention, a plurality of driven rotating members that are driven to rotate by a sheet having a toner image fixed on the guide member are arranged side by side, and the plurality of driven rotating members are arranged along the curl of the sheet passing through the guide member. Can be tilted. Thereby, even when the sheet is curled, a contact area with the sheet can be ensured, and as a result, the driven rotating member is reliably driven to rotate and the generation of the roller trace can be prevented.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing an overall configuration of a color laser printer which is an example of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention.

  In FIG. 1, 71 is a color laser printer, and 72 is a color laser printer main body (hereinafter referred to as a printer main body). The printer main body 72 includes an image forming unit 1A that forms an image on a sheet, a sheet feeding unit 20 that feeds the sheet, and a sheet fed from the sheet feeding unit 20 to the image forming unit 1A. And a fixing device 40 for fixing an image formed on the sheet.

  Here, the image forming unit 1A is configured by image forming units 1 (1a to 1d) which are arranged in the vertical direction and form toner images of four colors of yellow, magenta, cyan and black, respectively. Further, each image forming unit 1 includes a photosensitive drum 2 (2a to 2d) that is an image carrier that carries toner images of four colors of yellow, magenta, cyan, and black. The photosensitive drum 2 is a negatively charged OPC photosensitive member having a photoconductive layer on an aluminum drum base, and is driven at a predetermined process speed in the direction of an arrow (clockwise) by a driving device (not shown). Driven by rotation.

  Each image forming unit 1 includes a charging device 3 (3a to 3d) and an exposure device 6 (6a to 6d) arranged around the photosensitive drum 2 in the rotation direction. Here, the charging device 3 uniformly charges the surface of the photosensitive drum to a predetermined negative potential with a charging bias applied from a charging bias power source (not shown).

  The exposure device 6 irradiates a laser beam modulated in accordance with a time-series electric digital pixel signal of image information to form an electrostatic latent image on a photosensitive drum. A polygon mirror (not shown) that rotates at a high speed is provided. Then, laser light is output from the laser output unit, and the surface of each photosensitive drum is exposed through a polygon mirror or the like that rotates at high speed, so that the surface of the photosensitive drum charged by the charger 3 has a static color of each color corresponding to image information. An electrostatic latent image is formed.

  Further, each image forming unit 1 includes a developing device 4 (4a to 4d), a cleaning device 5 (5a to 5d), and the like. Here, each developing device 4 stores toner of each color of yellow, magenta, cyan, and black, and each developing device 4 attaches each color toner to each electrostatic latent image formed on the photosensitive drum 2. Thus, the toner image is visualized. As a developing method by the developing device 4, for example, a two-component contact in which toner particles are mixed with a magnetic carrier is used as a developer and is conveyed by a magnetic force and developed in contact with each photosensitive drum 2. Development methods can be used.

  The cleaning device 5 (5a to 5d) removes the toner remaining on the surface of the photosensitive drum after the transfer, and removes and collects the transfer residual toner remaining on the surface of the photosensitive drum by a blade member (not shown). I am doing so.

  Incidentally, 34 (34a to 34d) is provided inside a transfer belt 31 which is an endless sheet conveying member for conveying a sheet to be described later, and sandwiches the transfer belt 31 together with the four photosensitive drums 2 (2a to 2d). Transfer roller.

  Here, these transfer rollers 34 are connected to a transfer bias power source (not shown), and positive charges are applied from the transfer roller 34 to the sheet via the transfer belt 31 at the transfer portions Ta to Td. It is like that. By applying the transfer bias in this manner, the negative color toner images on the photosensitive drum are sequentially transferred onto the sheet in contact with the photosensitive drum 2 to form a multicolor image. .

  In this embodiment, the transfer roller 35 formed of an elastic member is used as the transfer unit. However, instead of the transfer roller 35, a high pressure is applied when the toner image is transferred to the sheet, and the transfer belt 31 is used. You may use the transfer blade which contact | abuts.

  The sheet feeding unit 20 includes a plurality of sheets P, a sheet feeding cassette 21 that is loaded on the bottom of the printer body, a pickup roller 22 that feeds the sheets P stored in the sheet feeding cassette 21, and the like. . When forming an image, the sheet P is separated and fed one by one by the pickup roller 22 from the sheet feeding cassette 21, and thereafter, the sheet P is sent to the sheet conveying unit 30 by a registration roller pair 24 at a predetermined timing. It is designed to be transported.

  The sheet conveying unit 30 includes a transfer belt 31 as a sheet carrier that is stretched between a driving roller 33 and a tension roller 32 and is disposed to face all the photosensitive drums 2 (2a to 2d). Here, the transfer belt 31 electrostatically attracts the sheet P to the outer peripheral surface facing the photosensitive drum 2 and circulates counterclockwise by the driving roller 33 so as to bring the sheet P into contact with the photosensitive drum 2. It has become.

  Then, the sheet P is conveyed to the transfer position by the transfer belt 31 by being electrostatically attracted to the transfer belt 31 that circulates in this way, and the toner image on the photosensitive drum 2 is transferred. In this embodiment, the transfer belt 31 is made of a dielectric resin such as a polycarbonate, a polyethylene terephthalate resin film, a polyvinylidene fluoride resin film, or the like.

  The fixing device 40 applies heat and pressure to the toner image transferred onto the sheet to fix the toner image on the sheet, and includes a fixing unit 40A having a fixing roller 41 and a pressure roller 42 incorporating a heating source 46. Yes. The pressure roller 42 is pressed against the fixing roller 41 by an urging means (not shown), and a nip is formed at a contact portion between the pressure roller 42 and the fixing roller 41.

  In addition, the fixing device 40 discharges the sheet P conveyed from the transfer belt 31 to the nip and a sheet discharge tray 51 installed on the upper surface of the apparatus main body 72. A fixing paper discharge roller pair 47 is provided. Further, the fixing device 40 includes a sheet conveying device 40 </ b> B that conveys a fixed sheet, which will be described later, to the fixing discharge roller pair 47.

  Next, an image forming operation of the color laser printer 71 configured as described above will be described.

  When an image formation start signal is issued, the sheet P accommodated in the paper feed cassette 21 is picked up by the pickup roller 22, and then passes through the conveyance path 23 to the registration roller pair 24 whose rotation is stopped. At the end, a loop is formed. The skew of the sheet P is corrected by forming a loop in this way.

  Thereafter, at the timing when the leading edge of the toner image on the most upstream photosensitive drum 2a is rotated and conveyed to the contact point (transfer portion Ta) with the electrostatic transfer belt 31, the leading edge of the toner image and the sheet P are contacted at the contact point. The registration roller pair 24 starts to rotate so as to coincide with the print start position. Accordingly, the sheet P is conveyed toward the transfer belt 31 and is adsorbed.

  On the other hand, when an image formation start signal is issued, the photosensitive drum 2 is driven to rotate clockwise and the surface of the photosensitive drum 2 is uniformly charged negatively by the charging device 3. Then, the exposure device 6 converts the image signal of the output image into an optical signal at the laser output unit, and the laser beam, which is the converted optical signal, scans and exposes each charged photosensitive drum 2 statically. An electrostatic latent image is formed.

  First, yellow toner is applied to the electrostatic latent image formed on the photosensitive drum 2a of the image forming unit 1a by the developing device 4a to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied. Attached to a visible image as a yellow toner image.

  The sheet P fed from the sheet feeding cassette 21 through the sheet conveyance guide 23 is synchronized with the timing at which the leading edge of the toner image on the photosensitive drum 2a is moved to the transfer portion Ta between the photosensitive drum 2a and the transfer roller 35a. It is conveyed to the transfer portion Ta by the transfer belt 31. Then, a yellow toner image is transferred onto the sheet P by the transfer roller 35a to which a transfer bias (polarity opposite to the toner (positive polarity)) is applied to the sheet P conveyed to the transfer portion Ta.

  Next, the sheet P on which the yellow toner image is transferred is moved to the image forming unit 1b positioned above by the sheet conveying belt 31. The magenta toner image formed on the photosensitive drum 2b of the image forming unit 1b in the same manner as the yellow toner image is transferred to the yellow toner on the sheet P previously transferred by the transfer roller 35b at the transfer portion Tb. It is transferred onto the image.

  Similarly, cyan and black toner images formed on the photosensitive drums 2c and 2d of the image forming units 1c and 1d are transferred to the yellow and magenta toner images transferred on the sheet P in the transfer portions Tc and Td. A full color toner image is formed on a sheet by sequentially overlapping. When the image is transferred from the photosensitive drum 2 to the sheet P, the transfer residual toner remaining on each photosensitive drum is removed and collected by each drum cleaning device 5.

  The sheet P onto which the four color toner images are transferred in this manner is separated from the electrostatic transfer belt 31 by the curvature of the driving roller 33 and guided to the fixing inlet guide 35 to the fixing device 40. It is brought in. Thereafter, the fixing device 40 is heated and pressurized to fix the toner image on the sheet P. The sheet P having the toner image fixed thereon is discharged by the fixing discharge roller pair 47. The paper is discharged to the tray 51, and a series of image forming operations is completed. When outputting a monochrome image, the above-described image forming process is performed only in the image forming unit 1d that forms a black image.

  By the way, the fixing device 40 includes a fixing roller 41 and a pressure roller 42 that constitute fixing means 40A for heating and pressing an unfixed toner image formed on a sheet. Further, a fixing discharge roller pair 47 that is a discharge unit for nipping and conveying the sheet and discharging it to the outside of the fixing device 40, a conveyance auxiliary roller 43 that is driven to rotate by contacting the sheet, and the sheet P are guided. Conveying guides 48a and 48b are provided. The conveyance auxiliary roller 43 is rotatably supported by a conveyance guide 48b below the conveyance guides 48a and 48b, which are guide members. The conveyance auxiliary roller 43 and the conveyance guides 48a and 48b constitute a sheet conveyance device 40B.

  In the present embodiment, as shown in FIG. 2, the conveyance auxiliary roller 43, which is a driven rotation member of the sheet conveyance device 40B, can freely rotate the roller main body 45, which is a rotating body that contacts the sheet, and the roller main body 45. And a support shaft 44 to be supported. The roller body 45 preferably has an outer diameter r4 of about 6 to 20 mm and a width h1 of about 5 to 40 mm, but is optimized depending on the specifications and size of the color laser printer 71.

  Here, an insertion hole 49 that is an insertion portion for allowing the support shaft 44 to pass therethrough is provided on a side surface of the roller body 45. The insertion hole 49 is provided with a holding portion 45a to which the support shaft 44 is loosely fitted when the roller body 45 rotates, and an inclination for allowing the roller body 45 to tilt with respect to the support shaft 44. And a space 45b.

  Here, the holding portion 45 a is formed in the center portion inside the insertion hole 49 so that the axial direction of the roller body 45, that is, the section (length) in the width direction is narrower than the length of the roller body 45 in the width direction. ing. The inner diameter r1 of the holding portion 45a is set larger than the diameter r3 of the support shaft 44 so that the support shaft 44 can be loosely fitted.

  The inclined space 45b is formed from the end of the holding portion 45a, which is the side end of the insertion hole 49, to the entrance of the insertion hole 49, and has a diameter r2 larger than the diameter r1 of the holding portion 45a. Yes. In addition, it is preferable to form the length of the inclined space 45b in such a way that the edge of the entrance of the insertion hole 49 does not touch the support shaft 44 when the roller body 45 is tilted.

  By forming the inclined space 45b as described above, the support shaft 44 does not touch the entrance edge of the insertion hole 49 regardless of how the roller body 45 is inclined with respect to the support shaft 44. In addition, the roller body 45 can rotate smoothly.

  By configuring the conveyance auxiliary roller 43 as described above, the roller body 45 is configured to easily tilt at an angle α, that is, to be easily equalized, as shown in FIG. At this time, it is desirable that the angle α is 1 ° to 20 °. In order to realize the angle, the inner diameter r1 of the holding portion 45a, the inner diameter r2 of the inclined space 45b, and the width direction of the holding portion 45a are described. The length h2 is optimized.

  Here, by configuring the conveyance auxiliary roller 43 in this way, as shown in FIGS. 3A and 3B, the sheet P discharged from the fixing nip N is U-shaped or inverted U-shaped in the width direction. Even if the curl is attached, it can be tilted according to the amount of curl. Then, the conveyance auxiliary roller 43 inclines in accordance with the amount of curl in this way, so that a contact area between the sheet P and the conveyance auxiliary roller can be ensured. As a result, the conveyance auxiliary roller 43 can be reliably driven and rotated by the sheet P, and the occurrence of roller traces due to the rotation failure of the conveyance auxiliary roller 43 can be prevented.

  Thus, in the present embodiment, a plurality of conveyance auxiliary rollers 43 are arranged in parallel with the conveyance guide 48b, and the plurality of conveyance auxiliary rollers 43 are arranged along the curl of the sheet P passing through the conveyance guides 48a and 48b. It is possible to incline. Thereby, even when the sheet P is curled, a contact area with the sheet can be secured. As a result, even when the sheet is curled, a contact area with the sheet can be ensured, and the conveyance auxiliary roller 43 can be reliably rotated to prevent the occurrence of a roller mark. Furthermore, by preventing the occurrence of roller marks in this way, high-quality image output can be realized.

  In the present embodiment, as shown in FIG. 2, a step is provided in the holding portion 45a of the insertion hole 49 of the auxiliary conveyance roller 43 and the inclination space 45b. However, as shown in FIG. Even if 45b is tapered, the same effect can be obtained.

  In the present embodiment, the conveyance auxiliary roller 43 is integrally formed of a resin material, but particularly in the vicinity of the fixing nip, a three-layer structure as shown in FIG. 5 is used to protect the image immediately after fixing. It is preferable to do. In FIG. 5, 401 is a holding layer constituting the holding portion 45a, 402 is a sponge layer disposed around the holding layer 401, and 403 is a tube-shaped resin film (for example, fluorine) disposed around the sponge layer 402. System heat shrinkable tube).

  By the way, in the present embodiment, the configuration in which four conveyance auxiliary rollers 43 are arranged in the width direction has been described, but of course, the number is not limited to four, and even if optimized according to product specifications and sizes, The present invention is effective.

  In the above description, the color laser printer has been described as an example of the image forming apparatus including the fixing device according to the present invention. However, the present invention can also be applied to a monochrome printer having a single photosensitive member. Further, the present invention can be applied not only to printers but also to other electrophotographic image forming apparatuses such as copying machines and facsimile machines. Further, the fixing unit 40A and the sheet conveying device 40B are arranged in the casing of the fixing device 40, and an example of a unit configuration for reducing the size of the fixing device 40 has been shown. However, the fixing unit and the sheet conveying device are separately provided. It may be provided.

1 is a schematic diagram illustrating an overall configuration of a color laser printer that is an example of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of a conveyance auxiliary roller provided in the sheet conveyance device. The schematic diagram explaining the effect of the said conveyance auxiliary | assistant roller. The figure which shows the other structure of the said conveyance auxiliary | assistant roller. The figure which shows the other structure of the said conveyance auxiliary | assistant roller. FIG. 6 is a schematic cross-sectional view of an image forming apparatus including a conventional fixing unit and a sheet conveying device. FIG. 3 is an enlarged schematic diagram of the conventional fixing unit and the sheet conveying apparatus. FIG. 6 is a diagram illustrating problems of the conventional fixing unit and the sheet conveying apparatus. FIG. 6 is a diagram for explaining a problem of a conveyance auxiliary roller provided in the conventional fixing unit and the sheet conveyance device.

Explanation of symbols

1A Image forming unit 40 Fixing device 40A Fixing means 40B Sheet conveying device 41 Fixing roller 42 Pressure roller 43 Conveying roller 44 Support shaft 45 Roller body 45a Holding portion 45b Inclination space 47 Fixing discharge roller pair 48a, 48b Conveying guide 49 Insertion hole 71 Color laser printer 72 Color laser printer body P Sheet

Claims (5)

In a sheet conveying apparatus that conveys a sheet on which a toner image is fixed by a fixing unit,
A guide member for guiding the sheet on which the toner image is fixed to the sheet over preparative discharge direction by the fixing means,
A rotating body having a cylindrical shape that is arranged side by side in a direction perpendicular to the sheet discharge direction of the guide member, is rotated by the sheet on which the toner image is fixed, and contacts the toner image fixing surface of the sheet; A plurality of driven rotating members, each of which is configured by a support shaft that rotatably supports the rotating body, the tilting of the rotating body with respect to the support shaft;
The rotating body of the driven rotation member is arranged around the holding portion, an insertion portion into which the support shaft is inserted, a holding portion that is provided at an inner central portion of the insertion portion, and to which the support shaft is loosely fitted. A sheet conveying apparatus comprising: a sponge layer that is formed; and a tube-shaped fluororesin film disposed around the sponge layer.   2. The sheet conveying apparatus according to claim 1, wherein an inclination space having a diameter larger than an outer diameter of the support shaft that enables the rotation of the rotating body is provided at a side end portion of the insertion portion. .   3. The sheet conveying apparatus according to claim 2, wherein the length of the tilt space in the axial direction is set to a length that prevents the insertion portion from contacting the support shaft when the rotating body is tilted.   The sheet conveying apparatus according to claim 2, wherein the inclined space has a tapered shape. An image forming unit that forms a toner image and transfers the toner image to a sheet;
Fixing means for fixing the toner image transferred by the image forming unit to a sheet;
A sheet conveying device according to any one of claims 1 to 4,
An image forming apparatus comprising:

Images