JP2006243086A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent white part discharge in an area where a photoreceptor comes close to a transfer medium. <P>SOLUTION: A destaticizing part equipped with a light guide is adopted as a destaticizing part 19, and the light guide is arranged to be opposed proximately to the photoreceptor drum 21 rotating around a predetermined rotary shaft O21. Furthermore, the destaticizing part 19 is arranged so that the center light beam 105 of luminous flux emitted from the light guide may pass between a 1st virtual line 101 linking the emitted position 107 of the center light beam 105 and the rotary shaft, and a 2nd virtual line 103 linking the emitted position 107 and the downstream side end of a nip part 109 in a photoreceptor rotating direction D21. Thus, light quantity distribution is generated on the surface of the photoreceptor drum 21 so that light quantity radiated to the surface of the photoreceptor drum 21 may be increased as it advances from the downstream side end of the nip part to the downstream side in the photoreceptor rotating direction D21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a static elimination section provided with a light guide.

  In an image forming apparatus such as a copying machine, a printer, and a facsimile machine, a static eliminating unit, a charging unit, an image writing unit, and a developing unit are disposed around a photosensitive member as a latent image carrier. In such an image forming apparatus, in order to prevent an adverse effect on the image due to disturbance of the potential of the surface of the photoreceptor before charging as described in Patent Document 1, the image is removed by irradiating uniform light with a static eliminating unit. After removing the residual potential on the surface of the body, the surface of the photoreceptor is charged to a uniform potential (charging potential) by the charging unit. Next, an electrostatic latent image is formed on the surface of the photosensitive member by irradiating the surface of the photosensitive member with light from the image writing unit to remove the potential of the portion corresponding to the latent image. Then, as described in Patent Document 2, the toner charged to the same polarity as the previous charging potential is attached to the electrostatic latent image by the developing unit to form a visible image (toner development). The toner image visualized on the surface of the photoreceptor in this way is formed by a nip portion formed by contacting the photoreceptor and the transfer medium on a transfer medium whose surface is biased to a potential opposite to the toner potential. And in the transfer region including the vicinity thereof.

JP-A No. 13-142365 (paragraph numbers [0008] [0009] [0015] [0018]) JP-A-9-127804 (paragraph number [0013])

  However, in the above-described image forming apparatus, when an electrostatic latent image is not formed and the potential difference between the portion (white portion) where toner development is not performed in the development process as described above and the surface potential of the transfer medium is large, white Discharge (white portion discharge) may occur between the portion and the transfer medium. That is, the potential of the white portion is almost the same as the previous charging potential, whereas the surface potential of the transfer medium has a polarity opposite to the charging potential. At this time, if these potential differences are large, white portion discharge may occur in a region (proximity region) in which the photoconductor around the nip and the transfer medium are close to each other. Such white portion discharge becomes an obstacle to good image formation.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of forming a good image by preventing white portion discharge.

  In order to achieve the above object, the present invention forms a toner image by developing an electrostatic latent image with toner, a photoreceptor rotating around a predetermined rotation axis while carrying the electrostatic latent image on the surface thereof. Developing means; transfer means for bringing a transfer medium into contact with the photoconductor to form a nip portion; and transferring a toner image on the surface of the photoconductor to the transfer medium; a light-emitting member for discharging light; and a surface of the photoconductor A light guide that irradiates the surface of the photoconductor after the toner image is transferred to the transfer medium through the facing surface with light emitted from the light-emitting member for static elimination. The second imaginary line connecting the first imaginary line where the central ray of the light beam emitted from the opposing surface connects the emission position of the central ray and the rotation axis, and the downstream end of the nip portion in the photosensitive member rotation direction. Arranged to pass between the lines The image forming apparatus according to claim.

  In the image forming apparatus configured as described above, the light emitted from the light-emission light-emitting member is irradiated onto the surface of the photoreceptor through the light guide. For this reason, the light flux from the light guide becomes a broad light flux. Therefore, in the present invention, the light beam that guides light to the surface of the photosensitive member is passed through the first imaginary line and the second imaginary line through the central ray of the light beam emitted from the opposite surface of the light guide. Are arranged as follows. For this reason, a part of the light beam emitted from the light guide reaches a region (proximity region) where the photoconductor and the transfer medium around the nip portion are close to each other. Thereby, the potential difference between the transfer medium surface and the white portion of the photoreceptor surface in the adjacent region can be reduced, and the occurrence of the white portion discharge described above can be suppressed. Therefore, good image formation is possible.

  Further, in the present invention, a light guide that guides light from the light-emitting member for discharging to the surface of the photosensitive member is employed as a member that irradiates the photosensitive member with light. This light guide is different from the arrangement of a plurality of point light sources such as LEDs (Light Emitting Diodes), and it is not necessary to arrange a large number of light sources so as to face the photoconductor. It becomes possible to do. As a result, it is possible to provide a light amount distribution in which the amount of light applied to the surface of the photoconductor increases as it proceeds downstream from the transfer region including the nip portion and the vicinity thereof in the photoconductor rotation direction. And will be described in detail in the best mode for carrying out the invention). By adjusting the light amount distribution in this way, in the transfer region, while preventing excessively strong light, it is impossible to secure a sufficient potential difference between the white portion and the latent image portion, preventing image detrimental effects, By irradiating strong light from the transfer region to the downstream side in the rotation direction of the photosensitive member, the residual potential before charging is sufficiently removed, and uniform charging at the charging unit is enabled. Therefore, it is possible to prevent the adverse effect of the image due to the disturbance of the potential on the surface of the photoreceptor before charging, and to form a good image.

  Further, the light guide may be arranged so that a part of the light beam emitted from the light guide reaches the downstream end of the nip portion in the rotation direction of the photosensitive member. By arranging the light guide in this way, the occurrence of the white portion discharge described above can be suppressed even immediately near the downstream end of the nip portion. Therefore, good image formation is possible.

  In addition, the light guide is disposed so that the distance between the emission position on the first imaginary line and the photoconductor is shorter than the circumferential length between both ends in the photoconductor rotation direction of the region irradiated with light in the photoconductor surface. You may do it. By arranging the light guide in this way, the light amount distribution on the surface of the photoreceptor as described above is generated. Therefore, in the transfer area, the photoreceptor rotation direction from the transfer area is prevented while preventing an adverse effect on the image due to insufficient potential difference between the white part and the latent image part due to excessively strong light irradiation. By irradiating with strong light as it goes downstream, the residual potential before charging is sufficiently removed, and uniform charging in the charging unit is enabled. Therefore, it is possible to prevent the adverse effect of the image due to the disturbance of the potential on the surface of the photoreceptor before charging, and to form a good image.

  In addition, a plurality of image forming stations each having a photoconductor rotating around a predetermined rotation axis and developing the electrostatic latent images formed on the surface of the photoconductor into toner images of different colors are transferred. A color image is formed by arranging toner images formed on the surfaces of a plurality of photoconductors and superimposing them on the surface of the transfer belt to form a color image, and each of the plurality of image forming stations is arranged along the belt moving direction. In an image forming apparatus including a light-emitting member for static elimination that emits light and a light guide, in order to achieve the above-described object, the light guide has a facing surface that faces the surface of the photoconductor, and the light-emitting member for static elimination. The emitted light is applied to the surface of the photosensitive member after the toner image is transferred to the transfer belt through the opposing surface, and the central ray of the light beam emitted from the opposing surface is reflected by the emission position of the central ray and the rotation axis. The first imaginary line to be connected and the second imaginary line to connect the ejection position and the downstream end of the nip portion in the photoconductor rotating direction are disposed so as to be substantially parallel to the moving direction of the transfer belt. You may comprise as follows.

  In the image forming apparatus configured as described above, as described above, the central ray of the light beam emitted from the facing surface of the light guide passes between the first imaginary line and the second imaginary line, and the moving direction of the transfer belt Since the light guide is arranged so as to be substantially parallel to the light guide, the light irradiated from the light guide reaches a region (proximity region) where the photosensitive member and the transfer medium in the vicinity of the nip portion are close to each other. As a result, the potential difference between the transfer medium surface and the white portion of the photoreceptor surface in the adjacent region can be reduced, and the occurrence of the white portion discharge described above can be suppressed. Further, as described above, the light guide can be disposed opposite to the photoconductor. Therefore, it is possible to provide a light amount distribution on the surface of the photoconductor so that the amount of light applied to the surface of the photoconductor increases as it proceeds downstream from the transfer position in the direction of rotation of the photoconductor. Therefore, in the transfer area, the image is rotated from the transfer area to the photoconductor while preventing an adverse effect on the image due to insufficient potential difference between the white area and the latent image area due to excessively strong light irradiation. By irradiating with strong light as it goes downstream, the residual potential before charging is sufficiently removed, and uniform charging in the charging unit is enabled. Therefore, it is possible to prevent the adverse effect of the image due to the disturbance of the potential on the surface of the photoreceptor before charging, and to form a good image.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram showing an electrical configuration of the image forming apparatus of FIG. This device includes a color printing process for forming a full color image by superposing four color toners (developers) of black (K), cyan (C), magenta (M), and yellow (Y), and black (K). This is an image forming apparatus that selectively executes a monochromatic printing process for forming a monochrome image using only the toner. In this image forming apparatus, when an image forming command (printing command) is given to the main controller 510 from an external device such as a host computer, the engine controller 520 controls each part of the engine unit EG in accordance with the command from the main controller 510. Then, a predetermined image forming operation is executed, and an image corresponding to the image forming command is formed on a sheet (recording material) S such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  In the housing main body 3 included in the image forming apparatus of the present embodiment, an electrical component box 5 containing a power circuit board, a main controller 510 and an engine controller 520 is provided. An image forming unit 7, a transfer belt unit 9, and a paper feed unit 11 are also disposed in the housing body 3. In FIG. 1, a secondary transfer unit 12, a fixing unit 13, and a sheet conveying mechanism 15 are disposed on the right side in the housing body 3. The paper feeding unit 11 is configured to be detachable from the apparatus main body 1. The paper feeding unit 11 and the transfer belt unit 9 can be removed and repaired or exchanged.

  The image forming unit 7 includes image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) for forming a plurality of different color images. Each of the image forming stations Y, M, C, and K is provided with a photosensitive drum 21 on which the respective color toner images are formed. Each photosensitive drum 21 is connected to a dedicated drive motor and is driven to rotate at a predetermined speed in the direction of an arrow D21 in the drawing around the rotation axis O21. A charging unit 23, an image writing unit 29, a developing unit 25, a charge eliminating unit 19, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction. These functional units perform a charging operation, a latent image forming operation, a toner developing operation, and a charge eliminating operation. In FIG. 1, the image forming stations of the image forming unit 7 have the same configuration, and therefore, for convenience of illustration, only some image forming stations are denoted by reference numerals, and the other image forming stations are omitted. .

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface of the photosensitive drum 21 at the charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 21 as the photosensitive drum 21 rotates. Followed rotation. The charging roller is connected to a charging bias generator 5270 (FIG. 2), and is charged at a charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other by receiving the charging bias from the charging bias generator 5270. The surface of the body drum 21 is uniformly charged.

  The image writing unit 29 is an array writing in which elements such as a liquid crystal shutter including a light emitting diode and a backlight are arranged in a line in the axial direction of the photosensitive drum 21 (direction perpendicular to the paper surface of FIG. 1). The head is used and is spaced from the photosensitive drum 21. Further, the image writing unit 29 is electrically connected to an exposure control unit 5260 (FIG. 2). Based on a signal from the exposure control unit 5260, the image writing unit 29 irradiates the surface of the photosensitive drum 21 with light. An electrostatic latent image is formed. The array-like writing head has a shorter optical path length and is more compact than the laser scanning optical system. Therefore, it can be disposed close to the photosensitive drum 21 and has the advantage that the entire apparatus can be reduced in size.

  In this embodiment, the photosensitive drums 21, 17 M, 17 C, and 17 K of the photosensitive drums 21, the charging unit 23, the developing unit 25, and the photosensitive unit cleaner 27 of the image forming stations Y, M, C, and K (see FIG. It is unitized as 2). Each of the photoconductor cartridges 17Y, 17M, 17C, and 17K is provided with nonvolatile memories 910, 920, 930, and 940 for storing information related to the photoconductor cartridge. The transmission / reception units 530Y, 530M, 530C, and 530K provided on the respective photosensitive cartridges and the transmission / reception units 5220Y, 5220M, 5220C, and 5220K provided on the main body side are arranged close to each other, and the CPU 5210 of the engine controller 520 Wireless communication is performed with the memories 910, 920, 930, and 940. In this way, information on each photoconductor cartridge is transmitted to the CPU 5210, and information in each memory 910, 920, 930, 940 is updated and stored.

  Next, details of the developing section 25 (corresponding to “developing means” in the present invention) will be described on behalf of the image forming station K. The developing unit 25 includes a toner storage container 31 for storing toner, two toner agitation supply members 33 and 35 disposed in the toner storage container 31, and a partition member 37 disposed in proximity to the toner agitation supply member 35. And a toner supply roller 39 disposed above the partition member 37, a developing roller 41 that contacts the toner supply roller 39 and the photosensitive drum 21 and rotates in a direction indicated by an arrow at a predetermined peripheral speed. It is comprised from the control blade 43 contact | abutted.

  In each developing unit 25, the toner stirred and carried by the toner stirring supply member 35 is supplied to the toner supply roller 39 along the upper surface of the partition member 37. Further, the toner thus supplied is supplied to the surface of the developing roller 41 via the toner supply roller 39. The toner supplied to the developing roller 41 is regulated to a predetermined layer thickness by the regulating blade 43 and is conveyed to the photosensitive drum 21. Then, charging is performed at the developing position where the developing roller 41 and the photosensitive drum 21 are in contact with each other by the developing bias applied to the developing roller 41 from the developing bias generator 5280 (FIG. 2) electrically connected to the developing roller 41. The toner moves from the developing roller 41 to the photosensitive drum 21, and the electrostatic latent image formed by the image writing unit 29 is visualized.

  The toner image visualized at the development position is conveyed in the rotational direction D21 of the photosensitive drum 21, and then a nip portion 109 formed by contact between a transfer belt 53 (to be described later) and each photosensitive drum 21. Primary transfer is performed on the transfer belt 53 in the primary transfer region TR1 including FIG. 5 and the vicinity thereof. As described above, in the image forming apparatus according to this embodiment, the electrostatic latent image is formed by the image writing unit 29 on the surface of the photosensitive drum 21 that is uniformly charged by the charging unit 23. Then, after the electrostatic latent image is developed as a toner image by the developing unit 25, the toner image is transferred to the surface of the transfer belt 53. The principle of such a series of processes will be described in detail later.

  The neutralization unit 19 exposes the surface of the photosensitive drum 21 after the toner image is primarily transferred to the transfer belt 53 to remove residual potential on the surface of the photosensitive drum. It is disposed downstream of the transfer region TR1 so as to face the surface of the photosensitive drum 21. The positional relationship between the static eliminating unit 19 and the photosensitive drum 21 will be described in detail later.

  FIG. 3A is a diagram illustrating the configuration of the charge removal unit 19 as viewed from the direction perpendicular to the arrow D19 in the drawing, which is substantially parallel to the straight line connecting the primary transfer regions TR1 in each image forming station. It is. FIG. 3B is a perspective view thereof. In the present embodiment, the static elimination unit 19 includes two static elimination light emitting members 191 a and 191 b and a light guide 193, and has an integrated structure in which the light emission members 191 a and 191 b are respectively attached to both ends of the light guide 193. is doing. Further, as shown in FIG. 3, the structure is configured to be symmetric with respect to a symmetry axis 19X (broken line) in the Y-axis direction and the Z-axis direction.

  The light guide 193 is formed in a thin plate shape so that it can be disposed close to and opposed to the photosensitive drum 21. The light guide 193 has two light incident surfaces 194a and 194b on which light from the light-emitting members 191a and 191b for neutralization are incident at both ends in the major axis direction (left and right direction in FIG. 5A). , Two light reflecting surfaces 195a and 195b that reflect the incident light, and a light irradiation surface 196 that irradiates the surface of the photosensitive drum with the light that faces the photosensitive drum 21 and is reflected by each of the light reflecting surfaces 195a and 195b. Corresponding to “opposite surface” in the present invention. Further, the above-described symmetry axis 19X passes through the center of gravity of the light irradiation surface 196. Further, the light reflecting surfaces 195a and 195b extend in the major axis direction of the light guide 193 so as to approach the light irradiation surface 196 as they proceed from the respective ends of the light guide 193 to the inside of the light guide 193, and at the symmetry axis 19X. It is configured to be connected to each other.

  The neutralizing light-emitting members 191a and 191b are respectively disposed at both ends in the long axis direction of the light guide 193, and are opposed to the light incident surfaces 194a and 194b provided at both ends in the long axis direction of the light guide 193, respectively. LEDs 192a and 192b that are arranged to radiate light toward the inside of the light guide 193 are included therein.

  FIG. 3C is an enlarged view of the light reflecting surfaces 195a and 195b. As described above, the surface of each light reflecting surface is configured to have a number of step shapes as it proceeds from each end of the light guide 193 to the inside of the light guide 193 in the long axis direction of the light guide 193. The reason for configuring the surfaces of the light reflecting surfaces 195a and 195b in this way is as follows. In general, light emitted from a light source attenuates as the distance from the light source increases. Therefore, when the light reflectance of the surfaces of the light reflecting surfaces 195a and 195b is made uniform, the light reflecting surfaces 195a and 195b are reflected as the distance from the LEDs 192a and 192b, which are light sources that enter the light, increases. Light is reduced and unevenness occurs in the light irradiated from the light irradiation surface 196. Therefore, the above-described step shape is provided on the surfaces of the light reflecting surfaces 195a and 195b, and the light reflecting surfaces 195a and 195a and 195a and 195b have a higher reflectance as the distance from the LEDs 192a and 192b, which are light sources that respectively enter light, increases. A surface of 195b was constructed. With this configuration, uniform light is irradiated from the light irradiation surface 196, and the residual potential on the surface of the photosensitive drum 21 can be removed satisfactorily. Furthermore, in this embodiment, the static elimination part 19 is comprised so that it may become object centering | focusing on the symmetry axis 19X. Therefore, the central ray of the light beam emitted from the light irradiation surface 196 substantially coincides with the symmetry axis 19X.

  As described above, the static elimination unit 19 in the present embodiment reflects the light incident from the static elimination light emitting members 191a and 191b toward the light irradiation surface 196 facing the surface of the photosensitive drum 21 by the light reflection surfaces 195a and 195b. Thus, a light guide 193 configured to irradiate the surface of the photosensitive drum 21 with light uniform in the axial direction of the photosensitive drum 21 (left and right in FIG. 3) and remove the potential of the surface is employed. ing. The light guide 193 configured as described above can be reduced in size as compared with a structure in which a large number of LEDs are arranged facing the photosensitive drum 21, and the light guide 193 is disposed so as to be opposed to the photosensitive drum 21. be able to.

  Further, in this embodiment, a photoconductor cleaner 27 is provided in contact with the surface of the photoconductor drum 21 on the downstream side of the static eliminating unit 19 in the rotation direction D21 of the photoconductor drum 21. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to remove the toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 9 includes a driving roller 49 disposed below the housing body 3, a driven roller 51 disposed obliquely above the driving roller 49, and stretched around these rollers in the direction of an arrow D53 shown in the drawing. A transfer belt 53 that is circulated and a tension roller 55 that is biased in a direction in which the transfer belt 53 is stretched are provided. Further, the transfer belt unit 9 is disposed on the inner side of the transfer belt 53 so as to face the respective photosensitive drums 21 included in the image forming stations Y, M, C, and K when the photosensitive cartridge is mounted. 57Y, 57M, 57C, 57K. These primary transfer rollers (corresponding to “transfer means” in the present invention) are each electrically connected to a primary transfer bias generator 5290. These primary transfer rollers are brought into contact with the photosensitive drums 21 facing each other with the transfer belt 53 interposed therebetween, and the primary transfer bias is applied from the primary transfer bias generator 5290 at an appropriate timing. Thus, a primary transfer region including a nip portion 109 (FIG. 5) in which each photosensitive drum and the transfer belt 53 come into contact with each other and a toner image formed on the surface of each photosensitive drum 21 and the vicinity thereof. The image can be transferred onto the transfer belt 53 in TR1.

  The drive roller 49 circulates and drives the transfer belt 53 in the direction of the arrow D53 in the figure, and also serves as a backup roller for the secondary transfer roller 75. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the drive roller 49. Secondary transfer is omitted by grounding through a metal shaft. A conductive path of the secondary transfer bias supplied from the bias generation unit via the secondary transfer roller 19 is used. Thus, by providing the driving roller 49 with a rubber layer having high friction and shock absorption, the sheet S enters the contact portion (secondary transfer position TR2) between the driving roller 49 and the secondary transfer roller 75. At that time, it is difficult for the impact to be transmitted to the transfer belt 53, and deterioration of image quality can be prevented.

  The primary transfer rollers 57Y, 57M, and 57C are rotatable about a color rotation shaft 59 in the direction of an arrow D59 in the drawing and are rotatably supported on a color roller support frame 61 biased in that direction. It is supported. In addition, the color roller support frame 61 fixedly supports a plurality of charge removal units 19 included in each of the image forming stations Y, M, and C. Further, the color roller support frame 61 performs primary transfer when the arc surface of the color frame cam 65 fixed to the cam rotation shaft 63 rotated by the actuator 67 is brought into contact with the color roller support frame 61. The rollers 57Y, 57M, and 57C are in contact with the photosensitive drums 21 of the image forming stations Y, M, and C with the transfer belt 53 interposed therebetween, and a plurality of static elimination units 19 that are fixedly supported by the color roller support frame 61. The respective light irradiation surfaces 196 are configured so as to be close to the respective photosensitive drums 21 included in the respective image forming stations Y, M, and C. When the arc surface of the color frame cam 65 is removed from the color roller support frame 61, the primary transfer rollers 57Y, 57M, and 57C face the urging direction D59 of the color roller support frame 61, respectively. In addition to being separated from the photosensitive drum 21, the plurality of static eliminating portions 19 fixedly supported by the color roller support frame 61 are also separated from the opposing photosensitive drum 21. The actuator 67 is electrically connected to an actuator control unit 5250 (FIG. 2), and is configured such that the rotation angle of the actuator 67 is adjusted by a signal from the actuator control unit 5250 corresponding to a command from the CPU 5210. ing.

  The primary transfer roller 57K is rotatable about a monochrome rotation shaft 69 in the direction of arrow D69 in the drawing and is rotatably supported by a monochrome roller support frame 71 biased in this direction. Further, the monochrome roller support frame 71 fixedly supports the static eliminating unit 19 included in the image forming station K. The monochrome roller support frame 71 is primary when the arc surface of the monochrome frame cam 73 fixed to the cam rotation shaft 63 rotated by the actuator 67 is brought into contact with the monochrome roller support frame 71. The transfer roller 57K is in contact with the photosensitive drum 21 of the image forming station K with the transfer belt 53 interposed therebetween, and the light irradiation surface 196 of the static eliminating portion 19 fixedly supported by the monochrome roller support frame 71 is an image forming station. It is configured so as to be close to the photosensitive drum 21 of K. When the arc surface of the monochrome frame cam 73 is removed from the monochrome roller support frame 71, the primary transfer roller 57K is opposed to the photosensitive drum in the biasing direction D69 of the monochrome roller support frame 71. The static eliminator 19 that is fixedly supported by the monochrome roller support frame 71 is also separated from the photosensitive drum 21 that is opposed thereto.

  Further, in the present embodiment, the arc surface of the color frame cam 65 overlaps the arc surface of the monochrome frame cam 73 and is shorter than the arc surface of the monochrome frame cam 73. Therefore, by adjusting the rotation angle of the actuator 67 by the actuator control unit 5250, the primary transfer rollers 57Y, 57M, and 57C are kept in contact with the photosensitive drum 21 of the image forming station K. Can be separated or brought into contact with the photosensitive drum 21 facing each other. When the primary transfer rollers 57Y, 57M, and 57C are separated from the opposing photosensitive drums 21, the above-described tension roller 55 moves in the direction of tensioning the transfer belt 53 in conjunction with the separation operation. As a result, tension is applied to the transfer belt 53, and the transfer belt 53 is also separated from the photosensitive drum 21 of each of the image forming stations Y, M, and C. Accordingly, by appropriately adjusting the rotation angle of the actuator, the color printing process performed by bringing the transfer belt 53 into contact with all the photosensitive drums 21 of the image forming stations Y, M, C, and K, and the transfer belt 53 It is possible to selectively execute monochromatic printing processing performed only in contact with the photosensitive drum 21 of the image forming station K and separated from the photosensitive drum 21 of the image forming stations Y, M, and C. Further, since the actuator control unit 5250 is configured to adjust the actuator 67 in accordance with a command from the CPU 5210, the above-described color printing process or single color printing process can be selectively executed by issuing an appropriate command from the CPU 5210. .

  Further, when the arc surface of the monochrome frame cam 73 is separated from the monochrome roller support frame 71 by rotating the cam rotation shaft 63 from the state where the monochrome printing process is being executed, the primary transfer roller 57K Therefore, all the primary transfer rollers are separated from the opposing photosensitive drums 21, respectively. At this time, since the tension roller 55 is moved in the tensioning direction of the transfer belt 53 in conjunction with the separating operation of the primary transfer roller 57K, tension is applied to the transfer belt 53. Therefore, the transfer belt 53 is also an image forming station. K is separated from the photosensitive drum 21 of K.

  The sheet feeding unit 11 includes a sheet feeding unit having a sheet feeding cassette 77 in which sheets S are stacked and held, and a pickup roller 79 that feeds the sheets S from the sheet feeding cassette 77 one by one. The sheet S fed from the sheet feeding unit by the pickup roller 79 is fed to the secondary transfer position TR2 after the feeding timing is adjusted by the registration roller pair 81.

  The secondary transfer roller 75 is provided so as to be able to come into contact with and separate from the transfer belt 53 and is driven to come into contact with and separate from a secondary transfer roller driving mechanism (not shown). The fixing unit 13 includes a heating roller 83 that incorporates a heating element such as a halogen heater and is rotatable, and a pressure roller 85 that presses and biases the heating roller 83. The image secondarily transferred to the sheet S is fixed to the sheet S at a predetermined temperature at the contact portion between the heating roller 83 and the pressure roller 85. In the present embodiment, the fixing unit 13 can be disposed in a space formed obliquely above the transfer belt 53, in other words, in a space opposite to the image forming unit 7 with respect to the transfer belt 16. The heat conduction to the electrical component box 5, the image forming unit 7, and the transfer belt 53 can be reduced, and the influence of temperature fluctuations on these can be reduced. Further, the sheet S thus subjected to the fixing process is conveyed to a paper discharge tray 4 provided on the upper surface portion of the housing body 3 via a paper discharge roller pair 87.

  Further, as shown in FIG. 2, the apparatus includes a display unit 540 that is controlled by the CPU 5110 of the main controller 510. This display unit 540 is configured by, for example, a liquid crystal display, and in accordance with a control command from the CPU 5110, the operation guidance to the user, the progress of the image forming operation, the occurrence of an abnormality in the apparatus, the replacement timing of any unit, etc. A predetermined message for notification is displayed.

  In FIG. 2, reference numeral 5130 denotes an image memory provided in the main controller 510 for storing an image given from an external device such as a host computer via the interface 5120. Reference numeral 5230 is a ROM for storing a calculation program executed by the CPU 5210, control data for controlling the engine unit EG, and the like. Reference numeral 5240 is a RAM for temporarily storing a calculation result in the CPU 5210 and other data. is there.

  FIG. 4 is a diagram showing the principle of the process from charging by the charging unit 23 to transferring the toner image formed on the surface of the photosensitive drum 21 to the transfer belt 53. Hereinafter, the principle of the series of processes will be described in detail. First, the charging unit 23 uniformly charges the surface of the photosensitive drum 21 to the charging potential VC. Then, an electrostatic latent image is formed by irradiating the surface of the photosensitive drum 21 uniformly charged with the charging potential VC with light by the image writing unit 29 to remove the charge on the surface of the photosensitive drum 21. . At this time, the potential of the portion of the surface of the photosensitive drum 21 where the electrostatic latent image is formed becomes the electrostatic latent image potential VP.

  Next, the developing roller 41 that carries the toner and is biased to the developing bias potential VD having the same polarity as the charging potential is brought into contact with the photosensitive drum 21. At this time, since the toner carried on the developing roller 41 is charged with the same polarity as the charging potential VC, an electrostatic latent image is formed on the surface of the photosensitive drum 21 from the developing roller 41 as shown in FIG. It will move to the formed part. In this way, the electrostatic latent image is visualized on the surface of the photosensitive drum 21.

  Next, the surface of the photosensitive drum 21 carrying the visualized toner image is brought into contact with the primary transfer roller 53 with the transfer belt 53 interposed therebetween. At this time, as shown in FIG. 5, the transfer belt 53 forms a nip portion 109 at a contact position with the photosensitive drum 21. Then, the primary transfer roller 57 is biased to a primary transfer bias potential VT having a polarity opposite to the charging potential of the toner, so that the photosensitive drum 21 has a nip portion 109 and its vicinity (primary transfer region TR1). The toner image carried on the surface is transferred to the surface of the transfer belt 53. In the present embodiment, the potential of the portion (white portion) where the electrostatic latent image is not formed on the surface of the photosensitive drum 21 is the charging potential VC. On the other hand, the surface potential of the transfer belt 53 becomes the primary transfer bias potential VT. Therefore, a potential difference ΔV is generated between the white portion on the surface of the photosensitive drum 21 and the transfer belt 53. As described in the section “Problems to be Solved by the Invention”, when ΔV is large, white portion discharge occurs in a region (proximity region) where the photosensitive drum 21 and the transfer belt 53 around the nip portion 109 are close to each other. May occur, causing image damage.

  FIG. 5 is a diagram showing the positional relationship between the charge eliminating unit 19 and the photosensitive drum 21. As described above, in the present embodiment, the static eliminator 19 is disposed close to and opposed to the photosensitive drum 21, and the central light beam 105 of the light beam irradiated from the light irradiation surface 196 of the light guide 193 is emitted from the central light beam. It passes between a first imaginary line 101 connecting the position 107 and the rotation axis O21 and a second imaginary line 103 connecting the ejection position 107 and the downstream end of the nip portion 109 in the rotation direction of the photosensitive drum 21. Is arranged. Thereby, in the rotation direction of the photosensitive drum 21, it is possible to generate a light amount distribution on the surface of the photosensitive drum 21 such that the amount of light emitted increases from the vicinity of the downstream end of the nip portion 109 toward the downstream side. It becomes. The reason for this is as follows.

  In the present embodiment, the central light beam of the light beam emitted from the charge removal unit 19 passes through the nip portion side of the rotation axis O21 of the photosensitive drum 21. Therefore, a part of the light beam emitted from the static elimination unit 19 reaches the periphery of the nip portion 109. Further, the static eliminating unit 19 is disposed in close proximity to the photosensitive drum 21. As a result, the following effects occur.

  In general, light is the strongest at the light source, and is attenuated as it goes away from the light source and becomes 0 at infinity. Therefore, for example, when the light source is placed at the position P1 in FIG. 6, the light amount at the point A and the point B can be made different from the case where the light source is placed at the position P2. Because the position P2 is sufficiently away from the photosensitive drum 21, even if there is a slight difference in the distance from the light source between the point A and the point B, there is no great difference in the amount of light at each point. On the other hand, since the position P1 is close to the photosensitive drum 21, the difference in the distance from the light source at the point A and the point B affects the difference in the amount of light at each point. That is, the point A is irradiated with light stronger than the point B. With this effect, by arranging the light guide 193 close to the photosensitive drum 21, it is possible to generate a light amount distribution in which the amount of light irradiated increases from point B to point A.

More specifically, the apparatus configured as shown in FIG. 7 has the following remarkable effects. Here, a detailed example will be described. In the apparatus shown in FIG. 7, the neutralizing unit 19 is arranged so that the central beam 105 is parallel to the transfer belt 53 and the distance between them is 5 [mm]. In addition, the static eliminator 19 is arranged so that the distance between the emission position 107 and the nip downstream end (point A) in the direction component of the central ray 105 is 15 [mm]. By disposing the charge removal unit 19 in this way, the light emitted from the charge removal unit 19 reaches the downstream end (point A) of the nip portion. Under this arrangement condition, the charging potential VC is set to −600 [V], and the point (point) on the surface of the photosensitive drum 21 where the distance from the emission position 107 in the directional component of the point A and the central ray 105 is 7 [mm]. When the irradiation light quantity in each of B) was measured, it was 0.1 [μJ / cm ² ] at point A, but 0.3 [μJ / cm ² ] at point B. Further, the surface potential of the white portion at the point A was measured and found to be −300 [V]. This is a potential sufficient to make the electrostatic latent image visible while the surface potential of the portion where the electrostatic latent image is formed by exposure is −50 [V]. Therefore, an adverse effect on the image caused by insufficiently securing the potential difference between the white portion and the latent image portion by irradiating the transfer region in the vicinity of the nip portion 109 with excessively strong light is prevented. Further, by increasing the potential of the white portion from −600 [V] to −300 [V], the potential difference ΔV (FIG. 4) with respect to the primary transfer bias potential VT is reduced to suppress white portion discharge. It becomes possible.

  As described above, by disposing the charge eliminating portion 19 as in the present embodiment, the amount of light that increases as the amount of light irradiated increases from the downstream end of the nip portion toward the downstream side in the rotation direction D21 of the photosensitive drum 21. A distribution can be generated. As a result, the photosensitive drum 21 and the transfer belt 53 around the nip portion 109 are close to each other while irradiating relatively weak light around the primary transfer region and preventing image damage due to excessive light irradiation. In addition to preventing white-area discharge in the active area (proximity area), it is possible to irradiate relatively strong light in the area away from the primary transfer area, and before charging by the charging unit 23, the photosensitive drum 21 It was confirmed that the residual potential on the surface could be removed.

  As described above, in the present embodiment, the static elimination unit 19 including the light guide 193 is employed. As a result, the light guide 193 can be disposed close to and opposed to the photosensitive drum 21. Further, the neutralization unit 19 is configured such that the central ray 105 of the light beam irradiated from the light irradiation surface 196 of the light guide 193 has a first virtual line 101 connecting the emission position 107 of the central ray and the rotation axis O21, and the emission position 107. And the second imaginary line 103 that connects the downstream end of the nip portion 109 in the rotation direction of the photosensitive drum 21. As a result, in the rotation direction D21 of the photosensitive drum 21, it is possible to generate a light amount distribution in which the amount of light emitted increases from the downstream end of the nip portion toward the downstream side. Therefore, the photosensitive drum 21 and the transfer belt 53 in the vicinity of the nip portion 109 are close to each other while preventing a bad image caused by irradiating relatively weak light in the primary transfer region and irradiating excessive light. In addition to preventing white area discharge in the area, it is possible to irradiate relatively strong light in an area away from the primary transfer area, and to remove disturbance of the surface potential of the photosensitive drum 21 before charging by the charging unit 23. Can do. Therefore, good image formation is possible.

  Further, as described above, in the present embodiment, the static elimination unit 19 achieves the prevention of white portion discharge, which is the object of the present invention, and removes the disturbance of the surface potential of the photosensitive drum 21 before charging by the charging unit 23. Thus, it has two functions of preventing image damage due to the disturbance of the surface potential. However, as a device configuration, these functions may be shared by different functional units. In other words, for the purpose of preventing white portion discharge, a functional unit for removing disturbance of the surface potential of the photosensitive drum 21 before charging is provided separately from the neutralizing unit having the same basic configuration as the above embodiment. May be. In this case, the neutralization part intended for white part discharge irradiates a relatively weak light around the primary transfer area to prevent white part discharge, and an area separated from the primary transfer area by a separately provided functional part By irradiating with relatively strong light, it is possible to remove the disturbance of the surface potential of the photosensitive drum 21 before charging, and to prevent image defects due to the disturbance of the surface potential. Therefore, good image formation can be performed as in the present embodiment. However, it can be said that the apparatus configuration in the present embodiment is more preferable from the viewpoint of simplifying the apparatus configuration. Further, in the case of an apparatus that does not need to irradiate light on the surface of the photosensitive drum 21 in order to remove disturbance of the surface potential of the photosensitive drum 21 before charging, static elimination is performed only for the purpose of preventing white portion discharge. Just do it. In other words, the discharge of the charge eliminating member and the light guide according to the present invention irradiate relatively weak light around the primary transfer region, thereby preventing white portion discharge and enabling good image formation. At this time, it goes without saying that neutralization for the purpose of only preventing white portion discharge can be achieved by using the neutralization unit 19 according to the present embodiment.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. In the above-described embodiment, the neutralizing unit 19 is arranged so that the central beam is parallel to the transfer belt 53. However, for example, the distance between the ejection position 107 on the first imaginary line 101 and the photosensitive drum 21 (the distance between the surfaces) is the photosensitive drum rotation direction in the region of the surface of the photosensitive drum 21 where the light is irradiated. It may be shorter than the peripheral length (static elimination width) between both ends as a condition for determining the arrangement position of the static elimination unit 19. As described above, even when the static eliminating unit 19 is arranged, the light amount distribution as described above can be generated on the surface of the photosensitive drum 21. The reason will be described in detail with reference to FIG.

  Here, the case where the neutralization unit 19 is arranged at the broken line position and the case where the neutralization unit 19 is arranged at the solid line position will be described. Note that the two positions share the emission position of the central ray of the light beam emitted from the static elimination unit 19. Therefore, the inter-surface distance is the same L0 at the two positions. On the other hand, as shown by the broken line in the figure, the static elimination width when the static elimination unit 19 is arranged is L1. At this time, L1 is shorter than L0. On the other hand, if the static elimination unit 19 is disposed at the solid line position in order to obtain a static elimination width (L2) larger than the inter-surface distance, the light emitted from the static elimination unit 19 reaches the surface of the photosensitive drum 21 farther away. It will be. That is, by disposing the static elimination width to be large, the distance (L3) between the static elimination unit 19 and the closest point from the static elimination unit 19 in the region irradiated with light on the surface of the photosensitive drum 21. The distance (L4) between the static elimination unit 19 and the point farthest from the static elimination unit 19 can provide a greater difference in distance than when the static elimination unit is placed at the position of the broken line. Such a difference in distance generates a light amount distribution. Therefore, white portion discharge can be prevented and disturbance of the surface potential of the photosensitive drum 21 can be removed before charging by the charging unit 23. Therefore, good image formation is possible. Further, the developing method in the above embodiment uses a negatively charged toner, but the developing method is not limited to this, and the present invention can be applied to a toner using a positively charged toner. it can.

  Moreover, in the said embodiment, although the static elimination process is performed using two light emitting members, it is arbitrary about the number of light emitting members, a kind, arrangement | positioning position, etc., and the light which combined the light emitting member and the light guide. The present invention can be applied to all image forming apparatuses adopting a static elimination method. Furthermore, in the above embodiment, the present invention is applied to the color image forming apparatus. However, the application target is not limited to this, and the present invention can also be applied to a monochrome image forming apparatus. In short, the present invention can be applied to all image forming apparatuses in which a light guide is arranged in the vicinity of the downstream side of the transfer position to execute a charge removal process.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus. The figure which shows the structure of a static elimination part. The figure which shows the principle of the process from electrification to transfer. The figure which shows the positional relationship of a static elimination part and a photoreceptor drum. The figure which shows the generation reason of light quantity distribution. The figure which shows the positional relationship of a static elimination part and a photoreceptor drum. FIG. 5 is a diagram showing another embodiment of the image forming apparatus according to the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Apparatus main body, 17 ... Photoconductor cartridge, 19 ... Static elimination part, 21 ... Photoconductor drum, 53 ... Transfer belt, 57Y, 57M, 57C, 57K ... Primary transfer roller, 101 ... 1st virtual line, 103 ... 1st 2 imaginary lines, 105 ... central ray, 107 ... emission position, 109 ... nip part, 191a, 191b ... light emission member for static elimination, 193 ... light guide, 196 ... light irradiation surface, 5260 ... exposure control part, 5270 ... generation of charging bias , 5280... Development bias generator, 5290... Primary transfer bias generator, Y, M, C, K.

Claims (4)

A photoreceptor that rotates about a predetermined rotation axis while carrying an electrostatic latent image on its surface;
Developing means for developing the electrostatic latent image with toner to form a toner image;
A transfer means for bringing a transfer medium into contact with the photoconductor to form a nip portion and transferring the toner image on the surface of the photoconductor to the transfer medium;
A light-emitting member for static elimination that emits light;
A light guide having a facing surface facing the surface of the photosensitive member and irradiating the surface of the photosensitive member after the toner image is transferred to the transfer medium through the facing surface with light emitted from the light-emitting member for charge removal And
The light guide includes a first imaginary line in which a central ray of a light beam emitted from the facing surface connects an emission position of the central ray and the rotation axis, and a imaginary portion of the nip portion in the rotation direction of the photosensitive member. An image forming apparatus, wherein the image forming apparatus is disposed so as to pass through a second imaginary line connecting the downstream end.   The image forming apparatus according to claim 1, wherein the light guide is arranged so that a part of the light beam emitted from the light guide reaches a downstream end of the nip portion in a rotation direction of the photoconductor.   In the light guide, a distance between the emission position on the first imaginary line and the photoconductor is shorter than a peripheral length between both ends in the photoconductor rotation direction of a region irradiated with light in the surface of the photoconductor. The image forming apparatus according to claim 1, wherein the image forming apparatus is arranged as follows. A plurality of image forming stations each of which has a photoconductor rotating around a predetermined rotation axis and develops electrostatic latent images formed on the surface of the photoconductor into toner images of different colors are provided on the transfer belt. A toner image formed on the surface of the plurality of photoconductors is arranged along a moving direction, and a toner image formed on the surface of the plurality of photosensitive members is superimposed on the surface of the transfer belt to form a color image, and each of the plurality of image forming stations In an image forming apparatus comprising a light-emitting member for discharging light that emits light and a light guide,
The light guide has a facing surface facing the surface of the photoreceptor, and the surface of the photoreceptor after the toner image is transferred to the transfer belt through the facing surface with light emitted from the light-emitting member for charge elimination. A central ray of a light beam emitted from the facing surface is connected to the first imaginary line connecting the emission position of the central ray and the rotation axis, and the nip portion of the nip portion in the rotation direction of the photosensitive member and the emission position. An image forming apparatus, wherein the image forming apparatus is disposed so as to pass through a second imaginary line connecting to a downstream end and to be substantially parallel to a moving direction of the transfer belt.

Images