JP6185897B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a transfer device that transfers a toner image formed on an image carrier onto a sheet.

  In an image forming apparatus such as a copying machine, a printer, or a multifunction machine, a toner image formed on an image carrier is transferred onto a sheet by a transfer device. In the transfer device, the toner image is transferred to the paper by guiding the paper along a guide to a transfer nip formed between the image carrier and the transfer member, and applying a transfer bias to the transfer member.

  The guide that guides the sheet to the transfer nip has upper and lower guide plates that are arranged to face each other across the sheet conveyance path, and the sheet is placed in close contact with the image carrier as much as possible before the transfer bias is applied. By guiding, image defects due to pre-transfer, toner scattering, and abnormal discharge are suppressed. However, if a thick paper such as a postcard is guided by a guide fixed to the plain paper, the load on the paper from the guide increases due to the thickness of the paper and the strength of the paper. As a result, image defects such as a change in magnification and a dropout occur.

  In order to prevent the occurrence of image defects due to such a fixed guide, an image forming apparatus is disclosed in which a lower guide plate is rotatably supported. Patent Document 1 discloses an image forming apparatus including a rigid guide that is rotatably provided so that one end thereof is elastically biased toward an image carrier. Further, Patent Document 2 includes a guide that is supported so that the end portion on the image carrier side is bent, and in the case of thin paper, the end portion is in close contact with the image carrier without bending, and in the case of thick paper, the end portion is bent. A configured image forming apparatus is disclosed. Patent Document 3 discloses an image forming apparatus including a buffer member that protrudes in the direction of the image carrier from the lower surface of a flexible guide. Further, Patent Document 4 has a flexible guide that can swing in the direction of the image carrier, and is configured to restrict the swing of the guide in the direction opposite to the image carrier by a protruding portion. An image forming apparatus is disclosed.

Japanese Patent Laid-Open No. 06-130825 JP-A-2005-128482 JP 2008-26810 A JP 2012-203227 A

  However, when the lower guide plate is supported so as to be pivotable (swingable) as in the image forming apparatus described in Patent Documents 1 to 4, the lower guide plate and the upper guide plate are accurately positioned. There are cases where it is not. If the relative positions of the upper and lower guide plates are misaligned, the paper will not be transported in the proper direction even if the lower guide plate is rotated according to the thickness of the paper. There is a risk of image defects, streaks away from the guide, image timing defects, and the like.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of stably guiding a sheet to a transfer nip by accurately positioning upper and lower guide plates.

  In order to solve the above problems, an image forming apparatus of the present invention forms a transfer nip between an image carrier and a transfer member that transfers a toner image from the image carrier to a sheet in the transfer nip, An image forming apparatus comprising: a first guide member and a second guide member arranged to face each other across a conveyance path of the paper toward the transfer nip, wherein the first guide member is The end on the transfer nip side is biased in the direction approaching the second guide member, and a protrusion protruding in the direction of the second guide member is formed at the end on the transfer nip side. The second guide member is formed of a thin material having elasticity and guides the paper. The second guide member is disposed along a paper width direction intersecting with the paper conveyance direction. Separate the plate from the image carrier An elastic member that is displaceably supported in a direction; and a support member that supports the elastic member and has a positioning portion that contacts an end of the first guide member on the transfer nip side. In the guide member, the end portion on the transfer nip side is urged to contact the positioning portion of the support member, whereby the first guide member is positioned with respect to the support member, and the protrusion is The guide plate is configured to be positioned with respect to the first guide member by pressing the guide plate.

  By adopting such a configuration, the end portion on the transfer nip side of the first guide member and the guide plate of the second guide member are positioned with respect to the support member, so that the transfer of the first guide member is performed. The sheet can be reliably conveyed to the transfer nip from between the end portion on the nip side and the guide plate of the second guide member, and pre-transfer, toner scattering, image defects due to abnormal discharge, and the like can be prevented.

  In the image forming apparatus of the present invention, the positioning portion is provided at both ends of the support member in the sheet width direction, and the first guide member is in contact with both ends of the sheet width direction. The protrusions are formed close to the inner sides of both ends of the first guide member in the sheet width direction, and the end of the first guide member on the transfer nip side is the support member. The gap of the conveyance path between the first guide member and the guide plate may be regulated in a state where the protrusion is in contact with the positioning portion and the projection presses the guide plate.

  By adopting such a configuration, the gap in the transport path can be made constant in the paper width direction, so that the paper can be transported to the transfer nip in a constant posture, and image failure due to pre-transfer, toner scattering, and abnormal discharge. Etc. can be prevented.

  According to the present invention, since the first and second guide members can be accurately positioned, the sheet can be reliably guided to the transfer nip in a fixed posture, and image defects due to pre-transfer, toner scattering, and abnormal discharge can be prevented. Can be suppressed.

1 is a schematic diagram illustrating an outline of a printer according to an embodiment of the present invention. FIG. 4 is a front view illustrating a conveyance path between a registration roller pair and a transfer nip in the printer according to the embodiment of the invention. 3A and 3B are diagrams showing an end portion on the transfer nip side of the conveyance path between the registration roller pair and the transfer nip in the printer according to the embodiment of the present invention. FIG. 3A is a front view, and FIG. 3B is a side view as viewed from the right. 4 (A) and 4 (B) are front views showing the sheet conveying operation in the printer according to one embodiment of the present invention, and FIG. 4 (A) is a diagram of FIG. ) Indicates a postcard.

  Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings.

  First, the main configuration of the entire printer 1 (image forming apparatus) will be described with reference to FIG. FIG. 1 is a schematic diagram showing an outline of a printer according to an embodiment of the present invention. Hereinafter, the front side in FIG. 1 is the front side (front side) of the color printer 1, and the left and right directions will be described with reference to the direction viewed from the front of the printer 1.

  The printer 1 includes a box-shaped printer main body 2. A paper feed cassette 3 is provided at the lower part of the printer main body 2, and a paper feed unit 4 for feeding paper from the paper feed cassette 3 is provided at the upper left of the paper feed cassette 3. A registration roller pair 5 is provided at the upper right. A paper discharge tray 6 is provided at the top of the printer body 2. Above the inside of the printer main body 2, a toner container 7 containing toner and an exposure device 8 composed of a laser scanning unit (LSU) are arranged. An image forming unit 10 is provided below the exposure device 8.

  The image forming unit 10 is rotatably provided with a photosensitive drum 11 as an image carrier. Around the photosensitive drum 11, a charging device 12, a developing device 13, a transfer roller 14, a static eliminating device 15, and a cleaning device 16 are sequentially arranged along the rotation direction of the photosensitive drum 11. . Further, a fixing device 17 is provided on the right side of the image forming unit 10, and a paper discharge unit 18 facing the paper discharge tray 6 is provided above the fixing device 17.

  Further, inside the printer main body 2, the paper feed unit 4 passes through a registration roller pair 5, a transfer nip 19 formed between the photosensitive drum 11 and the transfer roller 14, and a fixing device 17. A paper transport path 20 toward the paper discharge unit 18 is provided. The conveyance path 20 branches to a reverse path 21 on the downstream side of the fixing device 17. The reverse path 21 joins the transport path 20 on the downstream side of the paper feeding unit 4.

  Next, an image forming operation of the printer 1 having such a configuration will be described. When image data is input from a computer or the like connected to the printer 1, an image forming operation is executed as follows.

  First, after the surface of the photosensitive drum 11 is charged by the charging device 12, exposure corresponding to image data is performed on the photosensitive drum 11 by laser light from the exposure device 8 (see the dotted line P in FIG. 1). Then, an electrostatic latent image is formed on the surface of the photosensitive drum 11. This electrostatic latent image is developed into a toner image by the developing device 13.

  On the other hand, the paper taken out from the paper feed cassette 3 or the manual feed tray (not shown) by the paper feed unit 4 is transferred along the conveyance path 20 after being matched with the image forming operation described above by the registration roller pair 5. It is conveyed to the nip 19. In the transfer nip 19, a transfer bias having a polarity opposite to the polarity of the toner is applied to the transfer roller 14, and the toner image on the photosensitive drum 11 is transferred to the sheet. The sheet on which the toner image has been transferred is separated from the photosensitive drum 11 by the static eliminator 15, transported downstream in the transport path 20, and enters the fixing device 17, where the toner image is fixed on the sheet. Is done. The paper on which the toner image is fixed is discharged from the paper discharge unit 18 onto the paper discharge tray 6. The toner remaining on the photosensitive drum 11 is removed by the cleaning device 16.

  Next, the conveying path 20 between the registration roller pair 5 and the transfer nip 19 will be described with reference to FIGS. 2, 3A, and 3B. FIG. 2 is a front view showing a conveyance path between the registration roller pair and the transfer nip. FIGS. 3A and 3B show an end of the conveyance path between the registration roller pair and the transfer nip on the transfer nip side. 3 (A) is a front view, and FIG. 3 (B) is a side view as seen from the right side.

  As shown in FIG. 2, between the registration roller pair 5 and the transfer nip 19, a pre-transfer upper guide member 31 (first guide member) and a pre-transfer lower guide member 41 (first guide) that form a conveyance path 20. 2 guide members) are supported by the printer main body 2 so as to face each other in the vertical direction.

  The pre-transfer upper guide member 31 is a plate-like member having a shape that is slightly convex upward and curved in an arc shape. As shown in FIGS. 3A and 3B, a protrusion 33 bent downward is formed on the edge (right edge) of the upper guide member 31 before transfer on the transfer nip 19 side. . Each protrusion 33 has the same height, and as shown in FIG. 3B, at the right edge of the pre-transfer upper guide member 31, it is inside the both ends 34 in the width direction perpendicular to the sheet conveyance direction. Therefore, it is formed outside the paper passing area W of the maximum width paper (for example, A4 landscape size) of the printer 1.

  As shown in FIG. 2, the pre-transfer upper guide member 31 can be rotated around a support shaft 35 extending in the paper width direction at substantially the center of the conveyance path 20 between the registration roller pair 5 and the transfer nip 19. Is supported by the printer body 2. Furthermore, the pre-transfer upper guide member 31 is biased downward by the biasing member 36 at the end (right end) on the transfer nip 19 side. As the biasing member 36, a coil spring or a torsion coil spring can be used.

  The pre-transfer lower guide member 41 includes a fixed lower guide plate 42 and a movable lower guide plate 43 (guide plate) provided in order along the paper transport direction. The fixed lower guide plate 42 is supported by the printer main body 2 so as to be inclined upward from the registration roller pair 5 toward the transfer nip 19.

  As shown in FIGS. 3A and 3B, the movable lower guide plate 43 has a length slightly longer than the width of the maximum width sheet passing area W, and a horizontally extending main body 43a. And an inclined portion 43b inclined slightly downward from the right edge of the main body portion 43a. A plurality of (for example, five) locking portions 43c extending in the left direction are formed at the left edge of the main body portion 43a at predetermined intervals along the paper width direction. The movable lower guide plate 43 is formed of a thin material that can be partially elastically deformed in the paper width direction. As such a material, for example, SUS (stainless steel) having a thickness of 0.1 mm or a resin can be used.

  The movable lower guide plate 43 is supported by a support member 45 provided so as to extend in the paper width direction via a plurality of elastic members 47.

  The support member 45 has a channel shape with an upper surface opened, and is positioned with respect to the printer body 2. The support member 45 has a left wall 45a and a right wall 45b facing each other, and a bottom wall 45c. The height of the left wall 45 a is formed lower than the height of the right end portion of the fixed lower guide plate 42. At a position near the upper end of the left wall 45a, a through hole 45d penetrating in the left-right direction and having a predetermined height is formed at a position corresponding to each locking portion 43c of the movable lower guide plate 43. The right wall 45b is formed lower than the left wall 45a.

  In addition, positioning portions 46 are provided at both ends of the support member 45 in the sheet width direction. Each positioning portion 46 is provided on the end surface of the right wall 45b in the sheet width direction so as to protrude above the left wall 45a. When the right end portion of the pre-transfer upper guide member 31 is urged by the urging member 36, both end portions 34 on the right edge of the pre-transfer upper guide member 31 abut against the upper end surface of the positioning portion 46, and each protrusion 33 hangs down above the right wall 45b.

  The elastic member 47 is formed of a plurality of (for example, five) compression coil springs, and a total of five ends on the bottom wall 45c of the support member 45, ie, both ends in the paper width direction and three places between both ends. It is arranged at equal intervals in places. Note that a method for supporting the elastic member 47 on the bottom wall 45 is not particularly limited, and fastening with screws, an adhesive, or the like can be applied. Further, as the elastic member 47, foamed sponge or solid rubber may be used, or a rectangular parallelepiped elastic member made of foamed sponge or solid rubber and having uniform elasticity in the vertical direction may be used. For example, a foamed sponge extending in the paper width direction may be attached to the upper surface of the bottom wall 45 of the support member 45.

  The elastic member 47 supports the movable lower guide plate 43 in a state where the respective locking portions 43 c of the movable lower guide plate 43 are inserted at positions close to the upper portions of the respective through holes 45 d of the support member 45. The movable lower guide plate 43 is prevented from coming off in the through hole 45d of the support member 45, for example, by bending the tip of the locking portion 43c. In the movable lower guide plate 43, the main body 43a extends horizontally from the left wall 45a of the support member 45 to the right side slightly from the right wall 45b, and the inclined portion 43b extends from the right edge of the main body 43a to the transfer nip 19. It is supported by the elastic member 47 so as to incline downward. There is a gap between the main body 43a and the right wall 45b of the support member 45, and the movable lower guide plate 43 is placed in the through hole 45d until the main body 43a contacts the right wall 45b of the support member 45. Can be moved downward and swingable.

  The positioning of the pre-transfer upper guide member 31 and the pre-transfer lower guide member 41 having the above configuration will be described. When the right end portion of the pre-transfer upper guide member 31 is urged by the urging member 36 and rotates about the support shaft 35, both end portions 34 at the right edge of the pre-transfer upper guide member 31 are positioned on the positioning portion of the support member 45. 46 abuts on the upper end surface of 46. As a result, the end (right end) on the transfer nip 19 side of the pre-transfer upper guide member 31 is positioned with respect to the support member 45.

  3A and 3B, the protrusion 33 formed on the right edge of the pre-transfer upper guide member 31 is in contact with the upper surface of the main body 43a of the movable lower guide plate 43. In contact therewith, the movable lower guide plate 43 is pressed downward. Thus, the movable lower guide plate 43 is positioned with respect to the pre-transfer upper guide member 31. The distance between the pre-transfer upper guide plate 31 and the main body 43a of the movable lower guide plate 43 is regulated by the height of the projection 33 over the sheet passing area W of the maximum width sheet. Accordingly, a paper discharge port 51 having a constant gap is formed between the pre-transfer upper guide plate 31 and the main body 43a of the movable lower guide plate 43 over the paper passing area W of the maximum width paper. The sheet passes through the transfer nip 19 through the sheet.

  Next, the sheet conveying operation from the registration roller pair 5 to the transfer nip 19 will be described with reference to FIGS. 4 (A) and 4 (B). FIG. 4A is a front view illustrating the transport operation of plain paper, and FIG. 4B is a front view illustrating the transport operation of the postcard.

  As shown in FIG. 4A, when the A4-sized plain paper P1 is transported, the plain paper P1 passes along the transport path 20 between the pre-transfer upper guide member 31 and the pre-transfer lower guide member 41. It is conveyed and guided so as to be directed toward the paper discharge port 51 above the movable lower guide plate 43. Then, after exiting from the paper discharge port 51, it hits the ridge line portion 43 d formed between the main body portion 43 a and the inclined portion 43 b of the movable lower guide plate 43, hits the surface of the photosensitive drum 11, and is conveyed to the transfer nip 19 as it is. Is done. Since the plain paper P1 is light and thin, the movable lower guide plate 43 is hardly displaced.

  On the other hand, even when a specific small-sized cardboard P2 such as a postcard (hereinafter, the postcard will be described for convenience) is conveyed, the postcard P2 is transferred to the pre-transfer upper guide member 31 as shown in FIG. 4B. It is transported along the transport path 20 between the front lower guide member 41 and guided to the upper side of the movable lower guide plate 43 toward the paper discharge port 51. Then, after exiting from the paper discharge port 51, it hits the ridge line portion 43 d of the movable lower guide plate 43, hits the surface of the photosensitive drum 11, and is conveyed to the transfer nip 19. At this time, since the postcard P2 has a high rigidity and a large thickness, the ridge line portion 43d of the movable lower guide plate 43 is pushed downward by the postcard P2. Then, the elastic member 47 disposed in the sheet passing area of the postcard P2 is compressed and the movable lower guide plate 43 bends downward, so that the postcard is conveyed to the transfer nip 19 without applying a load from the movable lower guide plate 43. Can be made.

  As described above, in the printer 1 according to this embodiment, the pre-transfer upper guide member 31 is positioned with respect to the support member 45 positioned with respect to the printer main body 2. Further, the movable lower guide plate 43 is positioned with respect to the pre-transfer upper guide member 31 by the protrusion 33 formed on the pre-transfer upper guide member 31. Therefore, the sheet can be reliably conveyed to the transfer nip 19 between the pre-transfer upper guide member 31 and the movable lower guide plate 43, and the toner scattering due to pre-transfer and the image defect due to abnormal discharge can be reliably prevented. Can do.

  Furthermore, the upper guide plate 31 before transfer has both end portions 34 in the sheet width direction in contact with positioning portions 46 provided on the support member 45, and the protrusion 33 formed slightly inside the both end portions 34 has a movable lower guide plate. 43 is pressed, so that the height of the paper discharge port 51 formed between the pre-transfer upper guide member 31 and the movable lower guide plate 43 can be made constant in the paper width direction. Accordingly, the sheet can be stably conveyed to the transfer nip 19 and toner scattering due to pre-transfer, image defects due to abnormal discharge, and the like can be more reliably prevented.

  Further, when a small-sized thick sheet such as a postcard is conveyed, the movable lower guide plate 43 bends downward in the area through which the sheet is passed, so the postcard P2 that passes through the transfer nip 19 is transferred. No large load is applied from the movable lower guide plate 43. Therefore, even when the postcard P2 is conveyed only by the rotation of the transfer roller 14, the conveyance speed of the postcard P2 does not decrease, and it is possible to prevent the occurrence of image defects such as a change in magnification and void. The specific small-size cardboard includes a greeting card and a small-size envelope, and is not limited to a postcard.

  Further, in the embodiment of the present invention, the case where the configuration of the present invention is applied to the printer 1 has been described. However, in another different embodiment, the present invention is applied to an image forming apparatus other than the printer 1 such as a copying machine, a facsimile machine, and a multifunction machine. You may apply the structure of invention.

  Furthermore, since the above description of the embodiment of the present invention describes a preferred embodiment of the image forming apparatus according to the present invention, there may be various technically preferable limitations. The technical scope of the present invention is not limited to these embodiments unless specifically described to limit the present invention. That is, the above-described components in the embodiment of the present invention can be appropriately replaced with existing components and the like, and various variations including combinations with other existing components are possible. The description of the embodiment of the present invention described above does not limit the contents of the invention described in the claims.

1 Printer (image forming device)
11 Photosensitive drum (image carrier)
14 Transfer roller (transfer member)
19 Transfer nip 20 Conveyance path 31 Pre-transfer upper guide member (first guide member)
33 Projection 41 Lower guide member before transfer (second guide member)
43 Movable lower guide plate (guide plate)
45 Support member 46 Positioning portion 47 Elastic member

Claims (2)

A transfer nip formed between the image carrier and a transfer member for transferring a toner image from the image carrier to a sheet in the transfer nip;
A first guide member and a second guide member which are arranged to face each other across a conveyance path of the sheet toward the transfer nip;
An image forming apparatus comprising:
The first guide member is biased in a direction in which the end portion on the transfer nip side approaches the second guide member, and the second guide member is disposed on the end portion on the transfer nip side. A protrusion protruding in the direction of
The second guide member is
A guide plate that is formed of a thin material having elasticity and guides the paper;
An elastic member that is disposed along a paper width direction intersecting with the paper conveyance direction and supports the guide plate so as to be displaceable in a direction away from the image carrier;
A support member that supports the elastic member and has a positioning portion with which the end portion on the transfer nip side of the first guide member abuts.
In the first guide member, the end portion on the transfer nip side is biased and abuts against the positioning portion of the support member, whereby the first guide member is positioned with respect to the support member, and the protrusion An image forming apparatus, wherein the guide plate is positioned with respect to the first guide member when a portion presses the guide plate. The positioning portions are provided at both ends of the support member in the paper width direction, and the first guide member is in contact with both ends of the paper width direction,
The protrusion is formed close to the inside of the both end portions in the paper width direction of the first guide member,
In the state where the end portion on the transfer nip side of the first guide member is in contact with the positioning portion of the support member and the protrusion presses the guide plate, the first guide member and the guide plate The image forming apparatus according to claim 1, wherein a gap of the conveyance path between the two is regulated.

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