JP4877924B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to a pre-transfer guide for guiding a sheet to a transfer position on the surface of a photosensitive drum as an image carrier. .

  In conventional image forming apparatuses such as copying machines, printers, and facsimile machines using an electrophotographic system, a charging process for uniformly charging the surface of the photosensitive drum as an image carrier, and the surface of the photosensitive drum is exposed to electrostatic. An exposure process for forming a latent image, a development process for developing an electrostatic latent image with toner (developer) to form a toner image, a transfer process for transferring the toner image on the photosensitive drum to a sheet, and a transfer process to the sheet An image is formed through a fixing process for fixing the toner image.

  In such an electrophotographic system, the transfer process for transferring the toner image onto the paper is an important process for determining the quality of the image formed on the paper. In order to perform optimal image formation, the surface of the photosensitive drum is used. It is necessary to transport the paper properly to the transfer position. Therefore, in order to guide the paper conveyed from the registration roller pair to the transfer position to a better position, a pair of pre-transfer guides that guide both sides of the paper are arranged upstream of the transfer position, thereby achieving high transfer performance. A secured image forming apparatus is known (see, for example, Patent Document 1).

By the way, in recent years, image forming apparatuses tend to be reduced in size and cost, and various measures have been taken to reduce the number of components and arrangement space incorporated in the main body of the image forming apparatus. As for the pair of pre-transfer guides for guiding the paper to the position, one of the pre-transfer guides is integrally formed with the housing of the developing unit arranged around the photosensitive drum, thereby reducing a part of the pre-transfer guides arranged. A known image forming apparatus is known.
JP 2003-345141 A

  However, in general, many developing units arranged in the image forming apparatus are configured to be detachable from the apparatus main body in order to facilitate maintenance work. A pre-transfer guide is attached to such a developing unit. If they are integrated, the pre-transfer guide may not be placed at the intended position due to the operation method when the development unit is mounted on the main body of the apparatus or due to errors in the members constituting the development unit. In some cases, a paper jam or an image formation failure occurs.

  In the present invention, in view of the above-described circumstances, when a part of the pre-transfer guide for guiding the sheet to the transfer position of the image forming unit is integrally provided in the developing unit configured to be detachable from the apparatus main body. Another object of the present invention is to provide an image forming apparatus in which the pre-transfer guide can be arranged at a target position regardless of an error in the mounting position of the developing unit.

  To achieve the above object, the present invention provides a photosensitive drum as an image carrier, a developing unit for forming a toner image on the surface of the photosensitive drum, and a toner image formed on the surface of the photosensitive drum as a sheet. A transfer roller for transferring the sheet, a surface guide member for guiding the sheet to a transfer position formed by the photosensitive drum and the transfer roller, a surface guide member for guiding the surface of the sheet, and the surface guide member across the sheet conveyance path In the image forming apparatus comprising a pair of pre-transfer guides that are provided at positions facing each other and configured to guide the back surface of the paper, the developing unit is configured to be detachable from the apparatus main body. The surface guide member is swingably attached to the developing unit with the upstream side in the transport direction as a fulcrum.

  According to the present invention, in the image forming apparatus configured as described above, an urging unit that urges the front surface guide member toward the back surface guide member is provided.

  According to the present invention, in the image forming apparatus having the above-described configuration, the pre-transfer guide is configured such that a predetermined gap is secured between the front surface guide member and the back surface guide member at least in a portion where the sheet passes. It is characterized by having.

  According to the present invention, in the image forming apparatus configured as described above, at least a portion of the surface guide member that is in contact with the sheet is formed of a conductive material, and is grounded via the conductive member. .

  According to the first configuration of the present invention, since the surface guide member is swingably engaged with the developing unit, the mounting position of the developing unit on the apparatus main body constitutes the mounting operation and the developing unit. Even if the front surface guide member is swung from a predetermined position due to an error of the member, the front end of the front surface guide member comes into contact with the back surface guide member due to the swinging of the front surface guide member. It will be guided to a good position.

  Further, according to the second configuration of the present invention, in the image forming apparatus having the first configuration, the biasing means for biasing the front end of the front surface guide member to the back surface guide member is provided. Even when using stiff paper such as paper, the front edge of the surface guide member is not swung upward by the pressure of the conveyed paper, and the paper is moved to a better transfer position. Can guide.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, a predetermined gap is provided between the front surface guide member and the rear surface guide member at least in a portion through which the sheet passes. By being configured to be secured, the conveyed paper is not subjected to an excessive load, and image formation defects such as jitter are prevented.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, at least a portion of the surface guide member that is in contact with the sheet is formed of a conductive material. Is grounded through the conductive member, so that the surface guide member is not charged even when it is rubbed with the paper to be transported, and the paper is attracted to the surface guide member to cause a paper jam or toner on the surface guide member. Can be prevented from being contaminated and the toner on the photosensitive drum is attracted before the toner image is transferred to the paper, resulting in poor image formation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing the overall configuration of an image forming apparatus according to the present invention. In this embodiment, a laser beam printer is exemplified as an example of the image forming apparatus. However, it goes without saying that the present invention can be applied to a copying machine, a facsimile machine, or the like other than the printer.

  As shown in FIG. 1, the image forming apparatus 1 includes a paper feed cassette 2 that accommodates paper P stacked on the lower part of the main body. Above this paper feed cassette 2 is formed a paper transport path 4 that extends substantially horizontally from the main body right side surface portion to the main body left side surface portion and further extends upward to the paper discharge portion 3 formed on the upper surface of the main body. The pickup roller 5, feed roller 6, intermediate conveyance roller 7, registration roller pair 8, pre-transfer guide 9, image forming unit 10, image fixing unit 11, and discharge roller pair 12 are sequentially arranged along the sheet conveyance path from the upstream side. Is arranged.

  The paper feed cassette 2 has a paper stacking plate 13 whose rear end in the paper transport direction is rotatably supported on the bottom surface of the paper feed cassette 2, and a front end of the paper stacking plate 13 is biased upward. A biasing means 14 is provided so that the stacked paper P is pressed against the pickup roller 5. A retard roller 15 is disposed in front of the paper feed cassette 2 so as to be in pressure contact with the feed roller 6. When a plurality of sheets are simultaneously fed by the pickup roller 5, The sheet P is rolled by the feed roller 6 and the retard roller 15, and only the uppermost sheet is conveyed.

  Then, the paper P that is rolled by the feed roller 6 and the retard roller 15 is conveyed to the registration roller pair 8 by the intermediate conveyance roller 7. The registration roller pair 8 includes a driving roller 16 and a driven roller 17 that is driven to rotate. The conveyed paper P is supplied to the image forming unit 10 with the timing adjusted by the registration roller pair 8. Will be. At this time, the sheet P is guided to the better transfer position described later by being guided by the pre-transfer guide 9 on both sides.

  The image forming unit 10 forms a predetermined toner image on the paper P by an electrophotographic process, and is an image carrier that is rotatably supported in a predetermined direction (direction indicated by an arrow A in FIG. 1). A certain photosensitive drum 18 and a transfer unit 19 disposed around the photosensitive drum 18, a developing unit 20, a cleaning unit 22, and a transfer unit disposed so as to face the photosensitive drum 18 across the paper transport path 4. The laser scanning unit (LSU) 23 is disposed above the roller 21 and the photosensitive drum 18. Each of these units is configured to be detachable from the apparatus main body in order to facilitate maintenance work.

  The charging unit 19 includes a conductive rubber roller 19 a to which a power source (not shown) is connected. The conductive rubber roller 19 a is disposed so as to contact the photosensitive drum 18. When the photosensitive drum 18 rotates, the conductive rubber roller 19a comes into contact with the surface of the photosensitive drum 18 and is driven to rotate. At this time, by applying a predetermined voltage to the conductive rubber roller 19a, the photosensitive drum 18 is rotated. The surface of the film is uniformly charged.

  Next, an electrostatic latent image is formed on the photosensitive drum 18 by a laser beam from the laser scanning unit (LSU) 23 based on the input image data, and toner is attached to the electrostatic latent image by the developing unit 20. A toner image is formed on the surface of the photosensitive drum 18, and the transfer roller 21 moves the toner image on the surface of the photosensitive drum 18 to a transfer position formed at the nip portion between the photosensitive drum 18 and the transfer roller 21. Transferred to the supplied paper P.

  The paper P on which the toner image is transferred is conveyed from the image forming unit 10 toward the image fixing unit 11. The image fixing unit 11 is disposed on the downstream side of the image forming unit 10 in the sheet conveying direction. The sheet P on which the toner image is transferred in the image forming unit 10 is heated by a heating roller 24 provided in the image fixing unit 11. , And the pressure roller 25 pressed against the heating roller 24 and heated, and the toner image transferred onto the paper P is fixed.

  The paper P on which image formation has been performed in the image forming unit 10 and the image fixing unit 11 is discharged to the paper discharge unit 3 by the discharge roller pair 12. On the other hand, after the transfer, the toner remaining on the surface of the photosensitive drum 18 is removed by the cleaning unit 22. Then, the photosensitive drum 18 is charged again by the charging unit 19, and thereafter image formation is performed in the same manner.

  Next, the pre-transfer guide 9 provided in the image forming apparatus 1 will be further described with reference to FIGS. FIG. 2 is a perspective view showing the pre-transfer guide 9 and the photosensitive drum 18 provided in the image forming apparatus of the present invention. FIG. 3 is a schematic diagram showing the surface guide member 26 provided integrally with the developing unit 20. The sheet P to be transported is expressed as a surface on which toner is transferred at the transfer position as a front surface and a surface contacting the transfer roller as a back surface.

  The pre-transfer guide 9 is a conveyance guide for guiding the sheet P conveyed to the transfer position by the registration roller pair 8 to a better position of the transfer position, and includes a surface guide member 26 that guides the surface of the sheet P. The rear surface guide member 27 is provided at a position facing the front surface guide member 26 across the paper transport path 4 and guides the rear surface of the paper P.

  As shown in FIG. 2, the front surface guide member 26 and the rear surface guide member 27 are rectangular plate members having substantially the same width as the width of the photosensitive drum 18, and are arranged so as to be orthogonal to the sheet conveyance direction. Has been. Further, the front surface guide member 26 is formed to be greatly curved in the short side direction, and is disposed so that only the front edge in the paper transport direction is in contact with the back surface guide member 27. Then, the sheet P enters from the rear end side of the pre-transfer guide 9 and is guided to the transfer position by the front surface guide 26 and the back surface guide 27.

  Further, when the transported paper P receives an excessive load from the pre-transfer guide 9, image formation defects such as jitter occur, and therefore the transported paper at both ends in the long side of the back surface guide member 27 on the paper transport surface side. By providing the ridge 27a at a position not in contact with P, a predetermined gap is ensured between the front end of the front surface guide member 26 and the back surface guide member 27 at least in a portion through which the paper P passes. It is configured not to be loaded.

  The surface guide member 26 is integrally provided on the lower surface of the housing of the developing unit 20 disposed above the sheet conveying path 4 in order to reduce the size of the main body of the image forming apparatus 1. Here, as described above, the developing unit 20 is configured to be detachable from the apparatus main body. However, the developing unit 20 is displaced from a predetermined position due to an error of a member constituting the developing unit 20, a mounting operation, or the like. In such a case, a predetermined gap is not ensured between the front surface guide member 26 and the back surface guide member 27, and a paper jam or an image formation failure may occur.

  Therefore, as shown in FIG. 3, the front surface guide member 26 hooks the engagement piece 26 a provided at the rear edge of the paper non-transport surface side in the paper transport direction onto the hook portion 20 a formed in the developing unit 20. Thus, the developing unit 20 is swingably engaged. Thus, even when the mounting position of the developing unit 20 is deviated from a predetermined position, the front surface guide member 26 swings, so that a predetermined gap is formed between the front end of the front surface guide member 26 and the back surface guide member 27. The sheet P is secured and guided to a good position.

  In addition, a spring 28 that biases the front end of the front surface guide member 26 toward the rear surface guide 27 is disposed between the non-conveying surface of the front surface guide member 26 and the lower surface of the developing unit 20. Even when stiff paper such as thick paper is used, the front end of the front guide member 26 is not swung upward by the pressing force of the transported paper P, and the paper P is brought to a good position. Can guide. The urging means provided on the surface guide member 26 is only required to prevent the surface guide member 26 from swinging upward due to a pressing force of cardboard or the like, and may be, for example, a leaf spring or a weight in addition to the spring.

  Furthermore, the surface guide member 26 is made of a conductive material such as iron and is grounded via the conductive member. Thus, even when the front surface guide member 26 rubs against the transported paper P, it is not charged, and the paper P is attracted to the front surface guide member 26 to cause a paper jam or when a toner image is transferred onto the paper P. It is possible to prevent the toner image from being disturbed and causing image formation failure. The surface guide member 26 can be formed of a non-conductive member such as resin. In that case, a conductive sheet or the like is affixed to at least a portion of the surface guide member 26 that contacts the paper. It is preferable to prevent the surface guide member 26 from being charged by grounding it. The surface guide member 26 may be grounded through a resistor, a Zener diode, or the like.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the gap between the front surface guide member 26 and the rear surface guide member 27 is secured by the ridges 27a provided on the rear surface guide member 27. A protrusion may be provided on the image forming portion, and a gap may be secured by the protrusion. Alternatively, a locking piece may be provided on the frame of the main body of the image forming apparatus 1, and the clearance may be secured by the locking piece. Good. In the above embodiment, the engaging piece 26a of the surface guide member 26 is swingable by engaging with the hooking portion 20a of the developing unit 20, but this is provided with a rotation shaft on the surface guide member 26. By supporting this on the developing unit 20, it is also possible to make it swingable.

  INDUSTRIAL APPLICABILITY The present invention can be used in image forming apparatuses such as copying machines, printers, and facsimiles. More specifically, the present invention is used as a pre-transfer guide for guiding paper to a transfer position on the surface of a photosensitive drum as an image carrier. can do.

FIG. 1 is a schematic configuration diagram showing an overall configuration of an image forming apparatus according to the present invention. FIG. 3 is a perspective view showing a pre-transfer guide and a photosensitive drum provided in the image forming apparatus of the present invention. These are schematic views showing a surface guide member provided integrally with the developing unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 9 Pre-transfer guide 10 Image forming part 18 Photosensitive drum 20 Developing unit 20a Hook part 21 Transfer roller 26 Surface guide member 26a Engagement piece 27 Back surface guide member 27a Projection 28 Spring (biasing means)

Claims (3)

A photosensitive drum as an image carrier, a developing unit for forming a toner image on the surface of the photosensitive drum, a transfer roller for transferring the toner image formed on the surface of the photosensitive drum to a sheet, A front surface guide member that guides the paper to a transfer position formed by the photosensitive drum and the transfer roller, and a front surface guide member that guides the front surface of the paper, and a position opposite to the front surface guide member across the paper conveyance path, In an image forming apparatus comprising a pair of pre-transfer guides constituted by a back guide member for guiding,
A biasing means for biasing the front surface guide member toward the back surface guide member side is provided,
The developing unit is configured to be detachable with respect to the apparatus main body, and the surface guide member is integrally provided in the developing unit, and the surface guide member is provided on the upstream side in the transport direction with respect to the developing unit. An image forming apparatus, wherein the image forming apparatus is swingably attached. 2. The guide according to claim 1, wherein the pre-transfer guide is configured to ensure a predetermined gap between the front surface guide member and the back surface guide member at least in a portion through which the sheet passes. Image forming apparatus. The image forming apparatus according to claim 1, wherein at least a portion of the surface guide member that is in contact with the sheet is formed of a conductive material and is grounded through the conductive member. .

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