JP6362417B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  In the image forming apparatus, the toner image carried on the image carrier is transferred to a sheet. After the transferred toner image is fixed on the sheet by the fixing unit, the sheet is discharged from the image forming apparatus.

  A sheet conveying unit including an endless conveying belt that adsorbs and conveys the sheet is disposed between the transfer unit that transfers the toner image to the sheet and the fixing unit. By transporting the sheet by sucking the sheet onto the transport belt, the toner image can be transported without being disturbed (Patent Document 1).

JP-A-8-310686

  In the conventional apparatus, a plurality of conveying belts are provided side by side in the width direction of the sheet intersecting with the sheet conveying direction. Therefore, the cost and space for an element for stretching a plurality of belts are required, and the assembly is troublesome. Therefore, it is conceivable to reduce the number of conveyor belts, dispose the conveyor belt in the center in the direction perpendicular to the sheet conveyance direction, and install conveyance guides having ribs on both sides in the width direction of the conveyor belt. However, when the rib and the sheet on which the unfixed toner image is rubbed, the rib is charged and the toner image is disturbed. This disturbance of the toner image is liable to cause image defects particularly on coated paper having high smoothness.

The image forming apparatus according to the present invention is provided at a position downstream of at least the upstream roller and the upstream roller in the sheet conveyance direction, which conveys the sheet on which the toner image is transferred by the transfer unit. A conveying belt supported by the downstream roller, a fixing unit for fixing the toner image on the sheet conveyed by the conveying belt to the sheet, and the transfer unit and the fixing unit. A guide unit that guides a sheet conveyed by a belt; and a guide unit that is disposed on both sides of the conveyance belt in a width direction of the sheet that intersects the sheet conveyance direction , and is rotated by being driven by the sheet. includes a rotating member, the rotating member, the sheet conveying direction of the rotation center and the downstream roller of the downstream roller in the sheet conveying direction And it is provided in contact with the sheet between the definitive downstream end.

  According to the present invention, it is possible to prevent the toner image from being disturbed between the transfer portion and the fixing portion.

1 is a cross-sectional view schematically showing the overall structure of an image forming apparatus according to the present invention. It is a figure explaining a comparative example. Explanatory drawing for demonstrating the generation | occurrence | production mechanism of an image defect. The perspective view for demonstrating 1st Embodiment of this invention. FIG. 3 is a cross-sectional view of the sheet conveying unit according to the first embodiment of the present invention. Sectional drawing of the sheet conveying unit which concerns on 2nd Embodiment of this invention.

(Configuration of the entire image forming apparatus)
First, the overall configuration of the image forming apparatus 1 according to an embodiment of the present invention will be described with reference to FIG. 1 schematically showing the overall structure of the image forming apparatus 1.

  A sheet feeding process by the sheet feeding unit 2 to the secondary transfer unit 4 will be described. The sheets are stored in feeding cassettes 61, 62, and 63 provided in the lower part of the image forming apparatus 1, and are fed from the feeding cassettes 61 to 63 by feeding rollers 61a, 62a, and 63a. In the present embodiment, a manual feed tray 64 that can be manually fed is provided on the side of the image forming apparatus 1, and the sheet can be fed from the manual feed tray 64 by a feed roller 64a. Has been.

  The sheets fed by the feeding rollers 61 a to 64 a are separated one by one by the separating unit, and are upstream of the secondary transfer unit 4 in the sheet conveyance direction (hereinafter simply referred to as “upstream”) via the conveyance path 3. It is conveyed to the registered registration roller pair 76. The registration roller pair 76 forms a loop by abutting the leading edge of the fed sheet against the nip portion, and the leading edge of the sheet is copied along the nip portion of the registration roller pair 76 by forming the loop. Is called. Thereby, the skew of the sheet is corrected. The registration roller pair 76 conveys the sheet to the secondary transfer unit 4 at a predetermined timing in accordance with the timing of image formation on the sheet, that is, the rotation of the intermediate transfer belt 31 on which the toner image is primarily transferred. . As described above, the registration roller pair 76 corrects the skew of the sheet and conveys the sheet to the secondary transfer unit 4 at a predetermined timing.

  Next, the image forming unit will be described. The surfaces of the four photosensitive drums 11Y to 11K are charged with uniform charges by the charging units 12Y to 12K, respectively. The laser scanners 13C to 13K receive yellow (Y), magenta (M), cyan (C), and black (K) image signals, respectively, and irradiate the drum surface with laser light in accordance with the image signals, and charge Is neutralized to form a latent image.

  The latent images formed on the photosensitive drum are developed with yellow, magenta, cyan, and black toners by developing units 14Y to 14K, respectively. The toner developed on each photosensitive drum is sequentially transferred to the intermediate transfer belt 31 which is an endless belt-like image carrier by the primary transfer rollers 35Y to 35K, and a full-color toner image is formed on the intermediate transfer belt 31. The

  The intermediate transfer belt 31 carries the first-transferred full-color toner image and conveys the full-color toner image to the secondary transfer unit 4 at the same timing as the sheet conveyance process. The intermediate transfer belt 31 is stretched around a driving roller 33, a tension roller 34, and a secondary transfer inner roller 32, and rotates when the driving roller 33 is driven to rotate. Further, the toner remaining on the intermediate transfer belt 31 is cleaned by the transfer cleaning unit 35.

  Next, the secondary transfer process by the secondary transfer unit 4 and subsequent processes will be described. The secondary transfer unit 4 includes a secondary transfer inner roller 32 and a secondary transfer outer roller 41 facing the secondary transfer inner roller 32. The secondary transfer unit 4 applies a predetermined pressure and an electrostatic load bias to the sheet at a nip portion between the secondary transfer inner roller 32 and the secondary transfer outer roller 41 to form a full-color toner image on the sheet. Secondary transfer.

  When the full-color toner image is secondarily transferred to the sheet by the secondary transfer unit 4, the sheet is conveyed to the fixing unit 5 by the sheet conveyance unit 42. The conveying belt 100 constituting the sheet conveying unit 42 is stretched by a driving roller 101 as a downstream roller and a driven roller 102 as an upstream roller, as shown in FIG. The conveyance belt 100 is rotationally driven in the direction in which the sheet is conveyed from the secondary transfer unit 4 to the fixing unit 5. The conveyance belt 100 is provided with an infinite number of suction holes, and the conveyance belt 100 conveys the sheet by adsorbing the sheet to the upper surface of the conveyance belt by a negative pressure generated by a fan (not shown).

  A sheet conveyance path from the secondary transfer unit 4 to the sheet conveyance unit 42 is defined by a lower guide 43 disposed between the secondary transfer unit 4 and the sheet conveyance unit 42. Since the toner image is transferred to the upper surface of the sheet in the secondary transfer unit 4, an upper guide for guiding the upper surface of the sheet is not provided above the lower guide 43. Therefore, the sheet is guided along the upper surface of the lower guide 43.

  The fixing unit 5 melts and fixes the toner image secondarily transferred to the sheet by applying a predetermined pressure by an opposing roller or belt or the like and a predetermined heat by a heat source such as a heater. The sheet on which the toner image is fixed is discharged onto the discharge tray 66 via the discharge conveyance path 82. Further, when image formation is performed on both sides of the sheet, the sheet S is conveyed to the reverse path 83 and is drawn from the reverse path 83 to the switchback path 84. Then, the front and rear ends are switched by reversing the rotation direction of the pair of reversing rollers 79 (switchback operation), and the reversing roller pair 79 is transported to the duplex transport path 85. After that, the sheet S of the subsequent job fed from the feeding cassettes 61 to 63 or the manual feeding tray 64 is re-matched at the same timing, and is conveyed again to the secondary transfer unit 4 through the registration roller pair 76. The

  The image forming process on the back surface (second surface) is the same as that on the above-described front surface (first surface), and thus the description thereof is omitted. When the sheet is reversed and discharged, the sheet S passes through the fixing unit 5 and then is pulled from the reverse path 83 to the switchback path 84. Then, due to the reverse rotation of the reverse A roller pair 78 and the reverse roller pair 79, the rear end at the time of feeding is set at the head, the sheet is withdrawn in the direction opposite to the fed direction, and is discharged to the discharge tray 66.

(Defective image between the transfer part and the fixing part)
Here, before describing the embodiment according to the present invention, a comparative example will be described with reference to FIG. In the conventional method in which a plurality of conveyor belts are stretched and rotationally driven, cost and space for stretching the plurality of conveyor belts are required, and the assembly is troublesome. Therefore, it is conceivable to reduce the number of conveying belts as in the comparative example shown in FIG. In other words, the conveyor belt 902 is installed only in the central portion in the direction intersecting the sheet conveyance direction (sheet width direction). Then, guides 901 on which ribs 901 a are formed are installed on both sides of the conveyor belt 902.

  FIG. 3 shows a mechanism of occurrence of an image defect when a sheet is guided by the conveyance rib 901a in FIG. When a sheet having a width longer than the width of the conveyance belt 902 is passed, the sheet on which the rib 901a and the unfixed toner image are placed rubs. Then, there arises a problem that the rib 901a is charged and the toner image is disturbed. As shown in FIG. 3, the leading end of the rib 901a is charged together with the sheet passing, and draws unfixed toner in the sheet passing. As a result, a portion where the toner is attracted in the transport direction becomes a dark streak, and an image defect occurs in which the periphery becomes thin. In particular, at the downstream end of the rib 901a in the sheet conveyance direction, as shown in FIG. 2B, the rib 901a protrudes upward from the portion of the conveyance belt wound around the roller. The contact force becomes strong and image defects are likely to occur. Note that the above-described image defects are likely to occur when transporting coated paper with high smoothness.

(First embodiment)
The configuration of the sheet conveying unit 42 of the image forming apparatus 1 according to the first embodiment will be described with reference to FIGS.

  FIG. 4A is a perspective view of the sheet conveying unit 42 as viewed from the front side of the apparatus. A rubber endless conveyance belt 100 provided in the sheet conveyance path is supported by a driving roller 101 and a driven roller 102 made of polyacetal (POM) which are arranged to face each other. A drive input gear 103 is fixed to the end of the drive roller 101, and drive is transmitted from a gear 105 fixed to an output shaft of a drive motor (not shown) via an idler gear 104. Accordingly, the conveyance belt 100 is rotated by driving of the drive motor.

  FIG. 4B is a perspective view of the sheet conveying unit 42 as viewed from the back side of the apparatus. The lower surface of the resin conveyance guide 106 and the resin duct member 107 form an air passage. Air is sucked by a fan (not shown) arranged on the back side of the apparatus, and negative pressure is generated by a suction hole of the transport belt 100, whereby the sheet is adsorbed to the transport belt 100 and transported. The conveyance guide 106 is provided with a conveyance rib 108 formed integrally with the conveyance guide 106. The conveying ribs 108 are arranged at positions that avoid end portions in the width direction of sheets of various sizes. As shown in FIG. 5, a delivery member 111 that guides the sheet conveyed by the conveyance belt 100 to the fixing unit is provided between the conveyance belt 100 and the fixing unit 5. The conveyance guide 106 and the delivery member 111 constitute a guide unit that guides the sheet between the secondary transfer unit 4 and the fixing unit 5.

  Next, the rotating member 110 provided in the conveyance guide 106 will be described with reference to FIGS.

  A shaft 109 and a rotating member 110 made of polyacetal (POM) are provided at the downstream end of the conveyance guide 106 in the sheet conveyance direction. The shaft 109 is held so as not to rotate with respect to the conveyance guide 106 by snap fitting or press fitting. On the other hand, the rotating member 110 is held rotatably with respect to the shaft 109. When the rotating member 110 abuts while the sheet is being conveyed, the rotating member 110 is driven and rotated by the frictional force between the rotating member 110 and the sheet. In addition, unevenness is formed at a position on the outer periphery of the rotating member 110 and in contact with the sheet.

  With reference to a cross-sectional view of the sheet conveying unit 42 in FIG. The position of the rotating member 110 in the sheet conveyance direction corresponds to the position of the driving roller 101 in the sheet conveyance direction. In other words, a direction parallel to the upper surface of the conveying belt 100 that contacts the sheet is defined as a sheet conveying direction 91. A rotating member 110 is disposed between a center line 92 that is orthogonal to the sheet conveyance direction 91 and passes through the rotation center of the driving roller 101 and an end line 93 that is orthogonal to the sheet conveyance direction 91 and passes through the downstream end of the conveyance belt 100. Be placed. That is, the rotating member 110 is disposed so as to contact the sheet downstream of the center line 92 and upstream of the end line 93.

  The sheet that has passed through the sheet conveying unit 42 is transferred to a fixing unit 5 including an upper fixing belt 112 and a lower fixing belt 113 through a transfer member 111 as a pre-fixing guide.

  As described with reference to FIG. 2, if the rotating member 110 is not provided, the contact between the conveyance rib and the sheet is at a position corresponding to the driving roller 101 in the sheet conveyance direction (downstream end portion of the conveyance guide 106). strong. Specifically, the contact force with the sheet becomes stronger at the downstream end portion of the conveyance guide 106 and downstream of the position of the rotation center of the driving roller 101 of the conveyance belt 100 to the sheet transfer portion to the transfer member 111.

  Charging increases at the downstream end of the conveyance guide 106 where the sheet contact force is strong. In addition, since the contact force is strong, the degree to which unfixed toner in the sheet is attracted by charging increases. That is, the contact between the conveyance rib 108 and the sheet, which causes an image defect, becomes more conspicuous at the sheet delivery portion to the delivery member 111 downstream of the position of the rotation center of the driving roller 101 of the conveyance belt 100.

  In the present embodiment, a rotating member 110 that is in contact with the sheet and is driven by the sheet is provided at the end of the conveyance guide 106 and at a portion downstream of the rotation center of the driving roller 101. Since the rotating member 110 rotates following the sheet, it is less likely to be charged by sliding contact with the sheet, so that the occurrence of image defects due to the charging described with reference to FIG. 3 is prevented.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS.

  Fig.6 (a) is sectional drawing which showed 2nd Embodiment, FIG.6 (b) is a top view. In the first embodiment, a rotating member is provided at the downstream end of the conveyance guide 106, but in the second embodiment, a rotating member is provided at the upstream end of the delivery member 111.

  As in the first embodiment, in the sheet conveyance unit 42, the provided endless belt-shaped conveyance belt 100 made of rubber is suspended by a driving roller 101 and a driven roller 102 made of polyacetal (POM) which are arranged to face each other. Yes. The sheet that has passed through the sheet conveying unit 42 is transferred to the fixing unit 5 having the upper fixing belt 112 and the lower fixing belt 113 through the transfer member 111.

  A rotation member 110 made of polyacetal (POM) is provided at the upstream end of the delivery member 111 downstream from the rotation center of the drive roller 101. The rotating member 110 is rotatably held, and is rotated by the frictional force received by the sheet when contacting the sheet being conveyed.

  In any of the embodiments, the conveyance guide 106 is provided with the conveyance rib. However, a plurality of rotating members may be discretely arranged instead of the conveyance rib.

5 Fixing Unit 31 Intermediate Transfer Belt 100 Conveying Belt 110 Rotating Member

Claims (7)

A transfer portion for transferring the toner image to the sheet;
A conveyance belt supported by at least an upstream roller and a downstream roller provided downstream in the sheet conveyance direction with respect to the upstream roller, which conveys the sheet on which the toner image is transferred by the transfer unit;
A fixing unit for fixing the toner image on the sheet conveyed by the conveyance belt to the sheet;
A guide unit provided between the transfer unit and the fixing unit and guiding a sheet conveyed by the conveyance belt;
A rotation member provided in the guide means, disposed on both sides of the conveyance belt in the width direction of the sheet intersecting the sheet conveyance direction , and rotated by being driven by the sheet;
Have
The image forming apparatus , wherein the rotating member is provided so as to contact a sheet between a rotation center of the downstream roller in the sheet conveying direction and a downstream end of the downstream roller in the sheet conveying direction . The guiding means includes
A conveyance guide provided on both sides of the conveyance belt in the width direction;
A pre-fixing guide that is disposed between the conveyance guide and the fixing unit and guides a sheet conveyed by the conveyance belt to the fixing unit;
The image forming apparatus according to claim 1, wherein the rotating member is disposed at a downstream end portion of the conveyance guide facing an upstream end portion of the pre-fixing guide in the sheet conveyance direction. The guiding means includes
A conveyance guide provided on both sides of the conveyance belt in the width direction;
A pre-fixing guide that is disposed between the conveyance guide and the fixing unit and guides a sheet conveyed by the conveyance belt to the fixing unit;
The image forming apparatus according to claim 1, wherein the rotation member is disposed at an upstream end portion of the pre-fixing guide that faces a downstream end portion of the conveyance guide in a sheet conveyance direction. The conveyor belt is an endless conveyor belt that is supported and rotated by the upstream roller and the downstream roller,
The at least a part of the rotating member is disposed on an outer peripheral side of the conveying belt with respect to the conveying belt when viewed along the width direction of the sheet intersecting with the sheet conveying direction. The image forming apparatus according to any one of 1 to 3. Wherein the guide means, the image forming apparatus according to any one of claims 1 to 4, characterized in that another plurality of rotating members which are discretely arranged is arranged.   The image forming apparatus according to claim 1, wherein the conveyance belt includes a plurality of suction holes.   The image forming apparatus according to claim 1, wherein the surface of the rotating member that contacts the sheet is formed with irregularities.

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