JP2017203943A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can prevent a toner image transferred to a sheet from being disturbed between a transfer part and a fixing part.SOLUTION: An image forming apparatus comprises: a conductive member 472 that is arranged to face a lower surface of a sheet conveyed between a transfer part and a fixing part and electrostatically draws the sheet; and a first guide part that includes insulating ribs projecting from the surface of the conductive member 472 facing the sheet and guides the sheet toward the downstream in a conveyance direction. The conductive member 472 has opposite surfaces 472A1 in a first portion X1 that is part in a width direction of the sheet orthogonal to the conveyance direction separated from projecting ends of the ribs compared with opposite surfaces 472A2 in second portions X2 that are other parts in the width direction.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an electrophotographic image forming apparatus.

  An image forming apparatus such as a printer capable of forming an image by an electrophotographic method includes a transfer unit that transfers a toner image to a sheet. For example, the transfer unit includes a photosensitive drum and a transfer roller. A toner image is formed on the surface of the photosensitive drum. The transfer roller is provided in contact with the photosensitive drum, and a voltage having a predetermined polarity is applied thereto. The transfer unit transfers the toner image formed on the surface of the photosensitive drum onto the upper surface of the sheet. The sheet onto which the toner image has been transferred is conveyed to the fixing unit by the rotation of the photosensitive drum and the transfer roller. The fixing unit fixes the toner image transferred to the sheet to the sheet, and conveys the sheet on which the toner image is fixed toward the paper discharge unit.

  In addition, this type of image forming apparatus may include a metal plate-carrying guide having a metal plate and a rib and a resin-made conveyance guide between the transfer unit and the fixing unit (see Patent Document 1). The metal plate is disposed to face the lower surface of the sheet conveyed between the transfer unit and the fixing unit. The metal plate electrostatically pulls the sheet by a mirror image force acting between the sheet charged by the transfer roller. The ribs are provided so as to protrude from the metal plate in a direction opposite to the drawing direction of the sheet by the metal plate, and prevent contact between the sheet drawn to the metal plate and the metal plate. The conveyance guide with a metal plate guides the sheet to the resin conveyance guide. The resin conveyance guide guides the sheet guided by the metal plate-attached conveyance guide to the fixing unit. The behavior of the sheet conveyed from the transfer unit to the fixing unit is regulated by the conveyance guide with metal plate, and the sheet conveyance is stabilized.

JP 2010-32693 A

  In the image forming apparatus, the sheet conveyance speed by the transfer unit may be faster than the sheet conveyance speed by the fixing unit. In this case, convex or concave bending occurs on the upper surface of the sheet conveyed between the transfer unit and the fixing unit. Here, when the conveyance guide with a metal plate is provided in the image forming apparatus, since the sheet is attracted to the metal plate, the upper surface of the sheet is bent in a concave shape. However, if the sheet is weak, the leading edge of the sheet comes into contact with the resin conveyance guide and is excessively drawn to the metal plate, causing the sheet to bend between the sheet, the metal plate conveyance guide, and the resin conveyance guide. There may be no space left. In this case, there is a possibility that the toner image transferred to the sheet may be disturbed by contact with a cleaning unit or the like that cleans the photosensitive drum due to the upper surface of the sheet being bent convexly.

  An object of the present invention is to provide an image forming apparatus capable of preventing a toner image transferred to a sheet from being disturbed between a transfer portion and a fixing portion.

  An image forming apparatus according to the present invention includes a transfer unit, a fixing unit, a first guide unit, and a second guide unit. The transfer unit is rotatably provided, an image carrier on which a toner image is formed on the surface, and a transfer that is rotatably provided in contact with the image carrier and to which a voltage having a predetermined polarity is applied. A toner image formed on the image bearing member is transferred to a first surface of a sheet conveyed in a predetermined conveyance direction, and the sheet is conveyed at a predetermined first speed; The fixing unit is provided on the downstream side in the transport direction from the transfer unit, fixes the toner image transferred to the sheet by the transfer unit on the sheet, and sets the sheet to a second speed that is lower than the first speed. Carry in. The first guide portion is disposed opposite to the second surface opposite to the first surface of the sheet conveyed between the transfer portion and the fixing portion, and is set to the polarity by the transfer member. A conductive conductive member that electrostatically attracts the charged sheet; and an insulating rib that protrudes in a direction perpendicular to the facing surface from the surface of the conductive member facing the sheet; Guide to the downstream side in the transport direction. The second guide portion is provided on the downstream side in the transport direction from the first guide portion, and contacts the leading edge of the sheet in the transport direction to guide the sheet to the fixing unit. Further, the conductive member has the rib from the opposing surface of the second portion, wherein the opposing surface of the first portion which is a part of the width direction of the sheet orthogonal to the conveying direction is the other portion of the width direction. Is spaced apart from the protruding end in a direction perpendicular to the facing surface.

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

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating the configuration of the charge removal unit, the first guide unit, and the second guide unit of the image forming apparatus according to the embodiment of the present disclosure. FIG. 3 is a diagram illustrating the configuration of the charge removal unit and the first guide unit of the image forming apparatus according to the embodiment of the present disclosure. FIG. 4 is a diagram showing the configuration of the conductive member of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram illustrating a sheet conveyance state in the sheet conveyance path of the image forming apparatus according to the embodiment of the present disclosure. FIG. 6 is a diagram illustrating a sheet conveyance state in the sheet conveyance path of the image forming apparatus according to the embodiment of the present disclosure. FIG. 7 is a diagram illustrating a configuration of the first guide unit of the image forming apparatus according to the embodiment of the present invention. FIG. 8 is a diagram illustrating a configuration of a conductive member of an image forming apparatus according to another embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

[Configuration of Image Forming Apparatus 10]
First, the configuration of the image forming apparatus 10 according to the embodiment of the present disclosure will be described with reference to FIGS. Here, FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 10. FIG. 2 is a cross-sectional view showing the configuration of the charge removal portion 46, the first guide portion 47, and the second guide portion 48. FIG. 3 is a schematic plan view showing the configuration of the charge removal unit 46 and the first guide unit 47. FIG. 4 is a perspective view showing the configuration of the conductive member 472. In FIG. 2, the conveyed sheet S is indicated by a two-dot chain line. Moreover, in FIG. 4, the 1st part X1 and the 2nd part X2 are shown with the dashed-two dotted line.

  For convenience of explanation, the vertical direction is defined as the vertical direction D1 in the installation state in which the image forming apparatus 10 can be used (the state shown in FIG. 1). Also, the front-rear direction D2 is defined with the right side surface of the image forming apparatus 10 shown in FIG. Further, the left-right direction D3 is defined with reference to the front of the image forming apparatus 10 in the installed state. In FIG. 4, the vertical direction D1, the front-rear direction D2, and the left-right direction D3 are shown based on the installation state of the conductive member 472 in the image forming apparatus 10.

  The image forming apparatus 10 is a printer having a print function for forming an image based on image data. The present invention is also applicable to image forming apparatuses such as facsimile machines, copiers, and multifunction machines.

  As shown in FIG. 1, the image forming apparatus 10 includes a housing 10 </ b> A, an image forming unit 3, and a sheet supply unit 4.

  The housing 10 </ b> A accommodates each component of the image forming apparatus 10. As shown in FIG. 1, the image forming unit 3 and the sheet supply unit 4 are provided inside the housing 10A. An operation display unit (not shown) and a paper discharge tray 50 are provided on the upper surface of the housing 10A. A user of the image forming apparatus 10 can cause the image forming apparatus 10 to execute various processes such as a printing process by operating the operation display unit.

  The image forming unit 3 can form an image by electrophotography based on image data input from an information processing apparatus such as an external personal computer. Specifically, as shown in FIG. 1, the image forming unit 3 includes a photosensitive drum 31, a charging device 32, an optical scanning device 33, a developing device 34, a transfer member 35, a cleaning device 36, and a fixing unit 37. .

  As shown in FIG. 1, the photosensitive drum 31 is provided at the center of the housing 10 </ b> A. As shown in FIG. 2, the photosensitive drum 31 includes a rotation shaft 31 </ b> A that extends along the left-right direction D <b> 3. For example, the rotation shaft 31A is rotatably supported by the internal frame of the housing 10A. The photosensitive drum 31 receives a rotational driving force transmitted from a motor (not shown) and rotates in the rotational direction D4 shown in FIGS. An electrostatic latent image is formed on the surface of the photosensitive drum 31. Here, the photosensitive drum 31 is an example of an image carrier in the present invention.

  The charging device 32 is disposed above the photosensitive drum 31 as shown in FIGS. 1 and 2. For example, the charging device 32 is provided apart from the surface of the photosensitive drum 31 as shown in FIG. The charging device 32 charges the surface of the photosensitive drum 31. Specifically, the charging device 32 charges the surface of the photosensitive drum 31 by generating a discharge with the photosensitive drum 31 by a voltage applied from a power source (not shown). For example, the charging device 32 charges the surface of the photosensitive drum 31 to positive polarity.

  As shown in FIG. 1, the optical scanning device 33 is disposed above the charging device 32. The optical scanning device 33 forms an electrostatic latent image on the surface of the photosensitive drum 31. Specifically, the optical scanning device 33 irradiates the surface of the photosensitive drum 31 charged by the charging device 32 with light based on the image data.

  As shown in FIGS. 1 and 2, the developing device 34 is disposed on the front side of the photosensitive drum 31. The developing device 34 develops the electrostatic latent image formed on the surface of the photosensitive drum 31 using toner. Specifically, the developing device 34 includes a developing roller 341 and a stirring member 342 as shown in FIG. The developing roller 341 is provided to face the surface of the photoconductive drum 31 and supplies toner to the surface of the photoconductive drum 31. As a result, a toner image is formed on the surface of the photosensitive drum 31. The stirring member 342 stirs the toner stored in the developing device 34 and frictionally charges the toner. For example, the toner accommodated in the developing device 34 is stirred by the stirring member 342 and charged positively.

  As shown in FIG. 2, the transfer member 35 is disposed below the photosensitive drum 31. As shown in FIG. 2, the transfer member 35 is rotatably provided in contact with the photosensitive drum 31. For example, the transfer member 35 is a roller member that is rotatably provided on the internal frame of the housing 10A. The transfer member 35 is a sheet on which the toner image formed on the photosensitive drum 31 by the developing device 34 is conveyed in the conveying direction D5 (see FIG. 1) at the transfer position P1 (see FIG. 1) in contact with the photosensitive drum 31. Transfer to the upper surface of S. Specifically, the transfer member 35 generates a discharge with the photosensitive drum 31 by a voltage applied from a power source (not shown), and transfers the toner image on the photosensitive drum 31 to the sheet S. For example, a negative voltage is applied to the transfer member 35 from the power source. Here, negative polarity is an example of a predetermined polarity in the present invention. Moreover, the conveyance direction D5 is an example of the predetermined conveyance direction in this invention. Further, the upper surface of the sheet S is an example of the first surface of the sheet in the present invention. The transfer member 35 may be applied with a positive voltage from the power source. In this case, positive polarity is another example of the predetermined polarity in the present invention.

  As shown in FIG. 1, the cleaning device 36 is disposed on the rear side of the photosensitive drum 31. The cleaning device 36 cleans the surface of the photosensitive drum 31 after the transfer of the toner image by the transfer member 35. For example, as shown in FIGS. 1 and 2, the cleaning device 36 includes a blade-like cleaning member 361 and a polishing roller 362. The cleaning member 361 comes into contact with the surface of the photosensitive drum 31 to remove the toner remaining on the surface of the photosensitive drum 31. The polishing roller 362 polishes the surface of the photosensitive drum 31 by rotating in contact with the surface of the photosensitive drum 31. The toner removed by the cleaning member 361 is transported to a toner storage container (not shown) by a transport member (not shown).

  As shown in FIG. 1, the fixing unit 37 is provided on the rear side of the housing 10 </ b> A. More specifically, the fixing unit 37 is provided at a position spaced apart from the transfer member 35 by a predetermined distance to the rear side (downstream side in the transport direction D5). The fixing unit 37 fixes the toner image transferred to the sheet S by the transfer member 35 on the sheet S. For example, the fixing unit 37 includes a fixing member 371 and a pressure member 372 as shown in FIG. The fixing member 371 is provided in contact with the pressure member 372, and the toner image transferred to the sheet S is heated and fixed on the sheet S at a fixing position P <b> 2 (see FIG. 1) in contact with the pressure member 372. The pressure member 372 presses the sheet S that passes through the fixing position P2. For example, the fixing member 371 is a belt member that is rotatably provided in the fixing unit 37. The pressure member 372 is a roller member that is rotatably provided in the fixing unit 37.

  The sheet supply unit 4 supplies the sheet S to the image forming unit 3. Specifically, as shown in FIG. 1, the sheet supply unit 4 includes a sheet conveyance path 40, a paper feed cassette 41, a pickup roller 42, a feed roller 43A, a retard roller 43B, a conveyance roller 44, a registration roller 45, and a charge removal unit. 46, a first guide portion 47, a second guide portion 48, a discharge roller 49, and a discharge tray 50.

  The sheet conveyance path 40 is a movement path of the sheet S formed between the paper feed cassette 41 and the paper discharge tray 50. For example, the sheet conveyance path 40 is formed by a pair of conveyance guide members provided in the housing 10A.

  As shown in FIG. 1, a conveyance roller 44, a registration roller 45, and a discharge roller 49 are arranged in the sheet conveyance path 40. The conveyance roller 44, the registration roller 45, and the discharge roller 49 convey the sheet S along the conveyance direction D5 shown in FIG. 1 when the driving force generated by a motor (not shown) is transmitted and rotates.

  As shown in FIG. 1, the photosensitive drum 31 and the transfer member 35 are disposed in the sheet conveyance path 40. For example, the photosensitive drum 31 and the transfer member 35 convey the sheet S along the conveyance direction D5 shown in FIG. 1 when the driving force generated by a motor (not shown) is transmitted and rotated. For example, the photosensitive drum 31 and the transfer member 35 convey the sheet S at a predetermined first speed. Here, the configuration including the photosensitive drum 31 and the transfer member 35 is an example of the transfer portion in the present invention.

  As shown in FIG. 1, a fixing unit 37 is disposed in the sheet conveyance path 40 on the downstream side in the conveyance direction D <b> 5 from the photosensitive drum 31 and the transfer member 35. For example, the fixing member 371 of the fixing unit 37 conveys the sheet S along the conveyance direction D <b> 5 shown in FIG. 1 by rotating by driving force generated by a motor (not shown). The fixing member 371 moves the sheet S to a second speed that is lower than the first speed in order to avoid the occurrence of a problem that the sheet S passing the transfer position P1 is pulled toward the fixing unit 37 and the transfer position of the toner image is shifted. Carry in. In the fixing unit 37, the pressure member 372 may be rotated by receiving a driving force.

  As shown in FIG. 1, the paper feed cassette 41 is provided at the bottom of the housing 10A. The paper feed cassette 41 accommodates a sheet S on which an image is formed by the image forming unit 3. For example, the sheet cassette 41 contains sheet members such as paper, coated paper, postcards, envelopes, and OHP sheets. The sheet feeding cassette 41 has a lift plate (not shown) that lifts the uppermost sheet S to a contact position with the pickup roller 42 among the plurality of sheets S accommodated. The lift plate is provided at the bottom of the paper feed cassette 41.

  The pickup roller 42 is provided above the front end of the paper feed cassette 41 as shown in FIG. The pickup roller 42 conveys the uppermost sheet S out of the plurality of sheets S accommodated in the paper feed cassette 41 from the paper feed cassette 41 to the feed roller 43A.

  As shown in FIG. 1, the feed roller 43 </ b> A is disposed on the front side of the pickup roller 42. The retard roller 43B is provided in contact with the feed roller 43A below the feed roller 43A. The feed roller 43 </ b> A conveys the sheet S conveyed from the paper feed cassette 41 by the pickup roller 42 to the sheet conveyance path 40. The retard roller 43B separates the uppermost sheet S from the other sheets S when a plurality of sheets S are conveyed from the paper feed cassette 41 by the pickup roller 42. The conveyance roller 44 conveys the sheet S conveyed to the sheet conveyance path 40 by the feed roller 43A to the registration roller 45 on the downstream side in the conveyance direction D5.

  As shown in FIG. 1, the registration roller 45 is downstream in the transport direction D5 from the transport roller 44 in the sheet transport path 40, and is upstream from the transfer position P1 of the toner image by the transfer member 35 in the transport direction D5. Provided. The registration roller 45 conveys the sheet S in the conveyance direction D5 by rotating in response to a rotational driving force transmitted from a motor (not shown).

  As shown in FIGS. 1 and 2, the static elimination unit 46 is provided on the downstream side in the conveyance direction D5 from the transfer position P1 in the sheet conveyance path 40. As shown in FIG. 2, the charge removal unit 46 is provided to face the lower surface of the sheet S conveyed along the conveyance direction D5 from the transfer position P1. The neutralization unit 46 neutralizes the sheet S charged by the transfer member 35 and separates the sheet S from the surface of the photosensitive drum 31.

  For example, as shown in FIG. 3, the static elimination unit 46 includes a plurality of static elimination needles 461 provided along the width direction (left-right direction D3) of the sheet S orthogonal to the conveyance direction D5. For example, as shown in FIG. 3, the charge removal unit 46 is provided with a recess 462 that is recessed downward. The static elimination needle 461 is disposed in the concave portion 462 of the static elimination unit 46 in a posture in which the leading end faces the lower surface of the sheet S conveyed from the transfer position P1. A positive voltage is applied to the static elimination needle 461 from a power source (not shown). As a result, corona discharge occurs at the tip of the static elimination needle 461, and positive charges are applied to the lower surface of the sheet S conveyed from the transfer position P1. Accordingly, the negative charge is reduced from the negatively charged sheet S by the negative voltage applied to the transfer member 35, and the sheet S is separated from the surface of the photosensitive drum 31 charged positively.

  As shown in FIGS. 1 and 2, the first guide portion 47 is provided on the downstream side in the transport direction D5 from the charge removal portion 46 in the sheet transport path 40. As shown in FIG. 2, the first guide portion 47 is provided to face the lower surface of the sheet S conveyed between the photosensitive drum 31 and the transfer member 35 and the fixing portion 37. The first guide unit 47 guides the sheet S that has passed through the charge removal unit 46 to the downstream side in the transport direction D5. Specifically, as shown in FIG. 2, the first guide portion 47 is inclined downward along the conveyance direction D5, and is conveyed between the photosensitive drum 31, the transfer member 35, and the fixing portion 37. The inclined surface 471 is opposed to the lower surface of the sheet S to be formed. Moreover, the 1st guide part 47 has the electrically-conductive member 472 and the rib 473 as FIG.2 and FIG.3 shows. Here, the lower surface of the sheet S is an example of the second surface of the sheet in the present invention.

  The conductive member 472 has conductivity and electrostatically attracts the sheet S charged to the negative polarity by the transfer member 35. Specifically, the conductive member 472 electrostatically pulls the sheet S downward by a mirror image force acting between the transfer member 35 and the negatively charged sheet S. For example, the conductive member 472 is provided on the inclined surface 471 as shown in FIGS. For example, the conductive member 472 is a metal plate member. As shown in FIG. 4, the conductive member 472 has a rear end bent downward. An engaging portion 472 </ b> C is provided at the bent portion of the rear end portion of the conductive member 472. The conductive member 472 is attached to the first guide portion 47 by engaging a protrusion 471A (see FIG. 2) provided at the rear end portion of the first guide portion 47 with an engagement portion 472C. Although not shown in FIG. 4, the front end portion of the conductive member 472 has the same configuration as the rear end portion. For example, the conductive member 472 is electrically grounded via a resistor (not shown).

  The rib 473 has an insulating property and prevents contact between the sheet S attracted to the conductive member 472 and the conductive member 472. Specifically, the rib 473 is provided so as to protrude in a direction perpendicular to the facing surface 472A from the facing surface 472A (see FIG. 3) of the conductive member 472 facing the sheet S. For example, as shown in FIGS. 3 and 4, the conductive member 472 includes a plurality of slits 472 </ b> B formed in a long shape along the transport direction D <b> 5. The rib 473 is provided so as to protrude from each of the slits 472B. For example, the rib 473 is formed integrally with the inclined surface 471 using resin or the like. Note that the rib 473 may be provided on the upper surface of the conductive member 472.

  As shown in FIGS. 1 and 2, the second guide portion 48 is located downstream in the conveyance direction D5 from the first guide portion 47 in the sheet conveyance path 40 and upstream from the fixing portion 37 in the conveyance direction D5. Provided. As shown in FIG. 2, the second guide portion 48 is provided to face the lower surface of the sheet S conveyed between the photosensitive drum 31 and the transfer member 35 and the fixing portion 37. The second guide part 48 contacts the leading edge of the sheet S in the transport direction D5 guided by the first guide part 47 and guides the sheet S to the fixing part 37. Specifically, as shown in FIG. 2, the second guide portion 48 has an inclined surface 481 that is inclined upward along the transport direction D5. For example, the second guide portion 48 is formed of resin.

  The discharge roller 49 discharges the sheet S on which the toner image is fixed by the fixing unit 37 to the discharge tray 50. The sheet S on which an image is formed by the image forming unit 3 is discharged to the paper discharge tray 50.

  In the image forming unit 3, an image is formed on the sheet S conveyed by the sheet supply unit 4 according to the following procedure. First, the surface of the photosensitive drum 31 is uniformly charged to a predetermined potential by the charging device 32. Next, the light scanning device 33 irradiates the surface of the photosensitive drum 31 with light based on the image data. Thereby, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 31.

  The electrostatic latent image formed on the surface of the photosensitive drum 31 is developed (visualized) as a toner image by the developing device 34. The toner image formed on the surface of the photoconductor drum 31 is conveyed to the transfer position P1 by the transfer member 35 by the photoconductor drum 31 rotating along the rotation direction D4.

  On the other hand, the sheet supply unit 4 supplies the sheet S to the transfer position P1 in parallel with the image forming operation by the image forming unit 3. Specifically, the sheet feeding cassette 41 lifts the sheet S stored in the sheet feeding cassette 41 to a contact position with the pickup roller 42 using the lift plate provided at the bottom of the sheet feeding cassette 41. The pickup roller 42 conveys the uppermost sheet S lifted to the contact position to the feed roller 43A. The sheet S conveyed from the paper feed cassette 41 by the pickup roller 42 is conveyed to the registration roller 45 by the feed roller 43 </ b> A and the conveyance roller 44. When a plurality of sheets S are conveyed from the sheet feeding cassette 41 by the pickup roller 42, the uppermost sheet S and other sheets S are separated by the retard roller 43B.

  The registration roller 45 conveys the sheet S to the transfer position P1 in synchronization with the timing at which the toner image is conveyed to the transfer position P1 by the photosensitive drum 31. For example, in the image forming apparatus 10, a sensor (not shown) that can detect the passage of the sheet S is provided on the upstream side in the transport direction D 5 with respect to the registration roller 45 in the sheet transport path 40. In the image forming apparatus 10, when the passage of the sheet S is detected by the sensor, the conveyance roller 44 is rotated by a control unit (not illustrated) for a predetermined time while the rotation of the registration roller 45 is stopped. Is done. As a result, the leading edge of the sheet S is abutted against a nip portion formed between the registration roller 45 and a driven roller 45A (see FIG. 1) provided to face the registration roller 45, and the skew of the sheet S. Is corrected. Further, in the image forming apparatus 10, the control unit sets the conveyance timing of the sheet S by the registration roller 45 based on the detection timing of the passage of the sheet S by the sensor. Then, the registration roller 45 conveys the sheet S to the transfer position P1 based on the conveyance timing set by the control unit. As a result, the toner image conveyed by the photosensitive drum 31 is transferred to the surface of the sheet S conveyed to the transfer position P1 at the conveyance timing, and an image is formed on the sheet S. The toner remaining on the surface of the photosensitive drum 31 is removed by the cleaning device 36.

  The sheet S on which the toner image has been transferred at the transfer position P1 is separated from the photosensitive drum 31 by the charge removal unit 46, and then guided to the first guide unit 47 and the second guide unit 48 and conveyed to the fixing unit 37. . Here, the sheet S is guided to the downstream side in the transport direction D5 by the rib 473 of the first guide portion 47 in a state of being drawn downward by the conductive member 472 of the first guide portion 47. Thereby, the behavior of the sheet S conveyed from the transfer position P1 to the fixing unit 37 is regulated, and the conveyance of the sheet S is stabilized.

  In the fixing unit 37, the toner image transferred to the sheet S is heated by the fixing member 371 and the pressure member 372. As a result, the toner image is fixed on the sheet S. The sheet S on which the toner image is fixed by the fixing unit 37 is conveyed to the discharge roller 49 by the rotation of the fixing member 371 and the pressure member 372. The discharge roller 49 discharges the sheet S after image formation conveyed from the fixing unit 37 to the discharge tray 50.

  Meanwhile, in the image forming apparatus 10, the conveyance speed (the first speed) of the sheet S by the photosensitive drum 31 and the transfer member 35 is set to be higher than the conveyance speed (the second speed) of the sheet S by the fixing unit 37. Has been. In this case, convex or concave bending occurs on the upper surface of the sheet S conveyed between the transfer position P1 and the fixing unit 37. Here, in the image forming apparatus 10, since the sheet S is attracted to the conductive member 472 by the conductive member 472 of the first guide portion 47, the upper surface of the sheet S bends in a concave shape. For example, when the strain of the sheet S is strong, as shown in FIG. 5, the sheet S is lifted upward by the second guide portion 48 after the front end T of the sheet S comes into contact with the second guide portion 48, A space in which the sheet S can bend is formed between the sheet S and the first guide portion 47 and the second guide portion 48.

  However, in the case where the sheet S is a weak sheet member such as thin paper, as shown in FIG. 6, the sheet S becomes the conductive member 472 after the leading end T of the sheet S comes into contact with the second guide portion 48. The space where the sheet S is bent may be lost between the sheet S and the first guide part 47 and the second guide part 48 due to being pulled too much. In this case, the upper surface of the sheet S is bent in a convex shape and comes into contact with the cleaning device 36 or the like, so that the toner image transferred to the sheet S may be disturbed. In contrast, in the image forming apparatus 10 according to the embodiment of the present disclosure, the toner image transferred to the sheet S is prevented from being disturbed between the photosensitive drum 31 and the transfer member 35 and the fixing unit 37. It is possible.

  Specifically, in the image forming apparatus 10, the conductive member 472 has a facing surface 472 </ b> A <b> 1 (see FIG. 4) of the first portion X <b> 1 that is a part of the width direction (left-right direction D <b> 3) of the sheet S orthogonal to the transport direction D <b> 5. The second surface X2 (see FIG. 4), which is the other portion of the left-right direction D3, is spaced from the facing surface 472A2 (see FIG. 4) in the direction perpendicular to the facing surface 472A from the protruding end of the rib 473.

  For example, in the image forming apparatus 10, the facing surface 472A2 of the conductive member 472 is separated from the protruding end of the rib 473 by 1.0 millimeter in the direction perpendicular to the facing surface 472A. On the other hand, in the image forming apparatus 10, the facing surface 472A1 of the conductive member 472 is separated from the protruding end of the rib 473 by 2.0 millimeters in the direction perpendicular to the facing surface 472A.

  The strength of the mirror image force acting between the charged sheet S and the opposing surface 472A of the conductive member 472 is inversely proportional to the square of the distance between the sheet S and the opposing surface 472A. Therefore, in the facing surface 472A1, the mirror image force acting with the sheet S is weaker than that in the facing surface 472A2. In other words, in the image forming apparatus 10, the mirror image force acting on the sheet S can be reduced in a partial region in the left-right direction D 3 in the first guide portion 47. Accordingly, it is possible to adjust the image force acting on the sheet S from the conductive member 472 so that an excessive image force does not act on the sheet S when the weak sheet S such as thin paper is conveyed. Accordingly, it is possible to prevent the upper surface from being bent in a convex shape when the sheet S is conveyed between the photosensitive drum 31 and the transfer member 35 and the fixing unit 37, and the toner image transferred to the sheet S is disturbed. It is possible to prevent this.

  For example, the first portion X1 includes a central portion P3 (see FIG. 4) in the left-right direction D3 of the conductive member 472. For example, the first portion X1 is provided such that the central portion in the left-right direction D3 of the first portion X1 and the central portion P3 in the left-right direction D3 of the conductive member 472 coincide. Thereby, it is possible to stabilize the conveyance of the sheet S as compared with a case where the image force acting on both ends of the sheet S in the left-right direction D3 is reduced. A plurality of first portions X1 may be provided. For example, in the conductive member 472, the two first portions X1 may be provided to face each other across the center portion P3 in the left-right direction D3.

  The first portion X1 has a length in the left-right direction D3 that can form an image with the image forming apparatus 10 among the sheets S conveyed between the photosensitive drum 31, the transfer member 35, and the fixing unit 37. It is shorter than the length of the minimum size sheet S in the left-right direction D3. Thus, even when the image forming apparatus 10 transports the minimum size sheet S, the image force acting on both ends of the sheet S in the left-right direction D3 is not reduced, and the minimum size sheet S is transported. The loss of the stability of is avoided.

  For example, in the image forming apparatus 10, as shown in FIG. 7, a stepped portion 471 </ b> B that is recessed downward from the inclined surface 471 is provided on the inclined surface 471. 7 is a cross-sectional view taken along arrow VII-VII in FIG. Specifically, the step portion 471B is provided in a region corresponding to the first portion X1 of the conductive member 472. As shown in FIG. 7, the opposing surface 472A1 and the opposing surface 472A2 of the conductive member 472 are provided along the shape of the upper surface of the inclined surface 471. Further, as shown in FIG. 7, each of the ribs 473A protruding from the facing surface 472A1 is provided so as to protrude longer than the rib 473B protruding from the facing surface 472A2 by the level difference of the stepped portion 471B. Accordingly, the facing surface 472A1 is separated from the protruding end of the rib 473 from the facing surface 472A2. In the first portion X1, a plurality of facing surfaces 472A1 having different separation distances from the protruding ends of the ribs 473 may be provided.

  As described above, in the image forming apparatus 10, the conductive member 472 is provided with the facing surface 472 </ b> A <b> 1 and the facing surface 472 </ b> A <b> 2 having different separation distances from the protruding ends of the ribs 473. Thereby, it is possible to reduce the image force received from the conductive member 472 in a partial region of the sheet S in the width direction (left-right direction D3) orthogonal to the conveyance direction D5. Therefore, it is possible to adjust the image force acting on the sheet S from the conductive member 472 so that an excessive image force does not act on the sheet S when the weak sheet S such as thin paper is conveyed. Accordingly, it is possible to prevent the upper surface from being bent in a convex shape when the sheet S is conveyed between the photosensitive drum 31 and the transfer member 35 and the fixing unit 37, and the toner image transferred to the sheet S is disturbed. It is possible to prevent this.

  In the image forming apparatus 10, the conductive member 472 has an opening 472D provided in a part of the width direction (left-right direction D3) of the sheet S orthogonal to the conveyance direction D5, as shown in FIG. It may be. Also in this case, it is possible to reduce the mirror image force received from the conductive member 472 in a partial region of the sheet S in the left-right direction D3.

  Here, the opening 472D may include a central portion P3 (see FIG. 4) in the left-right direction D3 of the conductive member 472. For example, the opening 472D may be provided such that the central portion of the opening 472D in the left-right direction D3 and the central portion P3 of the conductive member 472 in the left-right direction D3 coincide. Thereby, it is possible to stabilize the conveyance of the sheet S as compared with a case where the image force acting on both ends of the sheet S in the left-right direction D3 is reduced. Note that a plurality of openings 472D may be provided. For example, in the conductive member 472, two openings 472D may be provided to face each other with the central portion P3 interposed therebetween in the left-right direction D3.

  Further, the opening 472D has a length in the left-right direction D3 of the minimum size sheet S among the sheets S conveyed between the photosensitive drum 31, the transfer member 35, and the fixing unit 37. It may be shorter than the length. Thus, even when the image forming apparatus 10 transports the minimum size sheet S, the image force acting on both ends of the sheet S in the left-right direction D3 is not reduced, and the minimum size sheet S is transported. The loss of the stability of is avoided.

3 Image forming unit 4 Sheet supply unit 10 Image forming device 31 Photosensitive drum 32 Charging device 33 Optical scanning device 34 Developing device 35 Transfer member 36 Cleaning device 37 Fixing unit 46 Charge removing unit 47 First guide unit 48 Second guide unit 471 Inclination Surface 472 Conductive member 472A Opposing surface 472B Slit 472C Opening 473 Rib

Claims (7)

An image carrier on which a toner image is formed on a surface, and a transfer member that is rotatably provided in contact with the image carrier and to which a voltage of a predetermined polarity is applied; A transfer unit that transfers the toner image formed on the image carrier to a first surface of a sheet conveyed in a predetermined conveyance direction and conveys the sheet at a predetermined first speed;
A fixing unit that is provided on the downstream side in the transport direction from the transfer unit, fixes the toner image transferred to the sheet by the transfer unit on the sheet, and transports the sheet at a second speed lower than the first speed. When,
The sheet charged between the transfer unit and the fixing unit is opposed to the second surface opposite to the first surface of the sheet and is charged to the polarity by the transfer member. A conductive conductive member that is electrically drawn, and an insulating rib that protrudes in a direction perpendicular to the facing surface from the surface facing the sheet of the conductive member, and guides the sheet downstream in the transport direction. A first guide part that
A second guide portion that is provided downstream of the first guide portion in the transport direction and contacts the leading edge of the sheet in the transport direction to guide the sheet to the fixing portion;
With
In the conductive member, the rib protrudes from the opposing surface of the second portion, the opposing surface of the first portion being a part of the width direction of the sheet orthogonal to the conveying direction. An image forming apparatus spaced apart from an end in a direction perpendicular to the facing surface.   The image forming apparatus according to claim 1, wherein the first portion includes a central portion in the width direction of the conductive member.   The first portion has a length in the width direction of the minimum size sheet capable of forming an image by the image forming apparatus among the sheets conveyed in the width direction between the transfer unit and the fixing unit. The image forming apparatus according to claim 2, wherein the image forming apparatus is shorter than the length. An image carrier on which a toner image is formed on a surface, and a transfer member that is rotatably provided in contact with the image carrier and to which a voltage of a predetermined polarity is applied; A transfer unit that transfers the toner image formed on the image carrier to a first surface of a sheet conveyed in a predetermined conveyance direction and conveys the sheet at a predetermined first speed;
A fixing unit that is provided on the downstream side in the transport direction from the transfer unit, fixes the toner image transferred to the sheet by the transfer unit on the sheet, and transports the sheet at a second speed lower than the first speed. When,
The sheet charged between the transfer unit and the fixing unit is opposed to the second surface opposite to the first surface of the sheet and is charged to the polarity by the transfer member. A conductive conductive member that is electrically drawn, and an insulating rib that protrudes in a direction perpendicular to the facing surface from the surface facing the sheet of the conductive member, and guides the sheet downstream in the transport direction. A first guide part that
A second guide portion that is provided downstream of the first guide portion in the transport direction and contacts the leading edge of the sheet in the transport direction to guide the sheet to the fixing portion;
With
The image forming apparatus, wherein the conductive member has an opening provided in a part of the width direction of the sheet orthogonal to the conveyance direction.   The image forming apparatus according to claim 4, wherein the opening includes a central portion in the width direction of the conductive member.   The opening has a length in the width direction of the minimum size sheet that can form an image in the image forming apparatus among the sheets conveyed in the width direction between the transfer unit and the fixing unit. The image forming apparatus according to claim 5, wherein the image forming apparatus is shorter than the length. The conductive member has a plurality of slits formed along the transport direction,
The image forming apparatus according to claim 1, wherein the rib is provided so as to protrude from each of the slits.

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