JP2005070596A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically obtain positional relationships when switching from a monochrome mode to a color mode takes place, in an image forming apparatus which has a plurality of color gears integrated with respective color image carriers and a black gear integrated with a black image carrier, and can select a color mode in which toner images formed on the color image carriers and the black image carrier are transferred to a recording medium or a monochrome mode in which only a toner image formed on the black image carrier is transferred to a recording medium, and in which the color gears and the black gear rotate while keeping the predetermined phase relationship so as to prevent color smear caused by their eccentricity in the color mode. <P>SOLUTION: Before switching from the monochrome mode to the color mode takes place by engaging an input idler gear 23 with the black gear 19BK and engaging an output idler gear 24 with the color gear 19M, the input idler gear 23 is rotated to the output idler gear 24. Thus, predetermined positional relationships between the black gear 19BK and the color gears 19Y, 19C, and 19M are obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention forms a black toner image on a black image carrier, and forms chromatic toner images of different colors on a plurality of color image carriers, and superimposes these toner images on a transfer material. The present invention relates to an image forming apparatus for transferring and obtaining a recorded image.

  An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile machine, or a multifunction machine having at least two of these functions has been conventionally known (for example, see Patent Document 1). This type of image forming apparatus is also called a tandem color image forming apparatus because a plurality of image carriers are arranged side by side. Such an image forming apparatus includes a direct transfer type image forming apparatus that directly superimposes and transfers each toner image formed on each image carrier to a transfer material made of a recording medium, and each image formed on each image carrier. The image forming apparatus can be divided into an intermediate transfer type image forming apparatus that transfers a toner image on a transfer material composed of an intermediate transfer member, and transfers the superimposed toner image onto a recording medium.

  Each type of image forming apparatus forms toner images of different colors on all image carriers, and in addition to a color mode in which these toner images are transferred onto a transfer material, the image forming apparatus is applied only to the black image carrier. A monochrome mode in which a black toner image is formed and the toner image is transferred to a transfer material can be selected. When the monochrome mode is selected, only the black image carrier among the color image carrier and the black image carrier is rotationally driven.

  The color image carrier and the black image carrier are connected to the color gear and the black gear arranged concentrically with each other, and each image carrier is rotated by rotationally driving these gears. I am letting. At this time, due to the eccentricity of the color gear and the black gear, uneven rotation may occur in the color image carrier and the black image carrier, which may cause color misregistration in the superimposed toner image transferred to the transfer material. There is. For this reason, conventionally, the color gear and the black gear are configured to rotate while maintaining a predetermined phase relationship so as not to cause color misregistration in the superimposed toner image transferred to the transfer material.

  However, in the monochrome mode in which the black image carrier is rotated together with the black gear to form a black toner image on the black image carrier, the color gear and the color image carrier are stopped. There is a risk that the predetermined phase relationship will be out of order and color misregistration will occur during the subsequent image forming operation in the color mode.

  Therefore, conventionally, there are provided two motors, a driving motor for rotating the black gear and a driving motor for rotating the color gear, and the black gear has the above-mentioned predetermined phase relationship at the end of the monochrome mode. It was comprised so that it might stop at the position where it is possible. However, according to this configuration, since two drive motors are required, the cost of the image forming apparatus increases.

  Alternatively, both the color gear and the black gear are rotated and driven by a single drive motor, and the clutch is controlled when switching from the monochrome mode to the color mode so that all the image carriers have a predetermined phase relationship. As described above, it is possible to adjust the circumferential position of each image carrier, but this configuration complicates the drive system of each image carrier and increases its cost.

Japanese Patent No. 3186559 (page 3-7, FIGS. 1 to 3)

  An object of the present invention is to provide an image forming apparatus in which the above-described conventional defects are eliminated.

  In order to achieve the above object, the present invention provides a plurality of color image carriers on which chromatic toner images are formed, one black image carrier on which black toner images are formed, and each color image carrier. And a color gear connected to each color image carrier so as to rotate together with each color image carrier, and concentrically arranged with respect to the black image carrier. Each color image carrier having a black gear connected to the black image carrier so as to rotate together with the black image carrier, and each color image carrier being rotated together with each color gear. A chromatic color toner image is formed, a black toner image is formed on a black image carrier that is rotationally driven together with the black gear, and the chromatic color toner image and the black toner image are superimposed on a transfer material and transferred to form a color image. Color mode, color gear and color image carrier It is possible to select a monochrome mode in which a black toner image is formed on a black image carrier that is stopped and rotated together with the black gear, and only the black toner image is transferred to a transfer material to obtain a black image. In the color mode, the color gears and the black gears are rotated while maintaining a predetermined phase relationship so that color misregistration does not occur in the superimposed toner image transferred onto the transfer material. An intermediate gear that meshes with a color gear coupled to each of the color image carriers adjacent to each other and drives and couples both color gears, and an input side that meshes with a black gear coupled to the black image carrier An idler gear, an output idler gear that meshes with a color gear connected to a color image carrier adjacent to the black image carrier, and rotation of the input idler gear in the color mode Connect the input-side idler gear and the output-side idler gear so that they are transmitted to the output-side idler gear. And a drive motor that rotationally drives the black gear or the input-side idler gear, and prior to switching from the monochrome mode to the color mode, the input-side idler gear is changed to the output-side idler gear. On the other hand, the color changing gear and the black gear are rotated to a predetermined position where a predetermined phase relationship is obtained, and then the rotation of the input side idler gear is transmitted to the output side idler gear by the switching means. An image characterized by connecting a side idler gear and an output side idler gear A forming apparatus is proposed (claim 1).

  In the image forming apparatus according to claim 1, it is advantageous to use an electromagnetic clutch as the switching means (claim 2).

  The image forming apparatus according to claim 1 or 2, further comprising a sensor that detects a mark attached to the input-side idler gear or a member that rotates integrally with the input-side idler gear, so that the monochrome mode is changed to the color mode. Prior to switching, it is advantageous that the switching means is operated to connect the input idler gear and the output idler gear based on a detection signal when the sensor detects the mark.

  In the image forming apparatus according to any one of claims 1 to 3, it is advantageous that the output gear of the drive motor is directly meshed with the input side idler gear or the black gear (claim 4).

  Furthermore, in the image forming apparatus according to any one of claims 1 to 4, it is advantageous that the input side idler gear, the output side idler gear, and the intermediate gear have the same number of teeth (claim 5).

  6. The image forming apparatus according to claim 1, wherein the number of teeth of the input idler gear, the output idler gear, and the intermediate gear is an integral multiple of the number of teeth of the output gear of the drive motor. This is advantageous (claim 6).

  Furthermore, in the image forming apparatus according to any one of claims 1 to 6, a gear having a larger number of teeth of the black gear and the input idler gear has a smaller number of teeth. It is advantageous that it is an integral multiple of the number of teeth.

  In the image forming apparatus according to any one of claims 1 to 7, the number of teeth of the gear having the larger number of teeth of the output idler gear and the color gear meshing with the output idler gear It is advantageous if it is an integral multiple of the number of teeth of the smaller gear (claim 8).

  Furthermore, in the image forming apparatus according to any one of claims 1 to 8, the number of teeth of the gear having the larger number of teeth of the color gear and the intermediate gear meshing with the color gear is a tooth number. It is advantageous if it is an integral multiple of the number of teeth of the smaller gear (claim 9).

  Further, in the image forming apparatus according to any one of claims 1 to 9, the thickness of one gear of at least one gear pair out of the gear pairs composed of two gears meshing with each other is larger than the thickness of the other gear. It is advantageous if it is formed thin and meshes with the other gear while one gear is within the thickness range of the other gear.

  Furthermore, in the image forming apparatus according to any one of the first to tenth aspects, it is advantageous that the color gear and the black gear are made of a resin gear formed by the same mold. 11).

  According to the present invention, even when the monochrome mode is switched to the color mode with a simple configuration, the color gear and the black gear can be rotated while maintaining a predetermined phase relationship. The occurrence of color misregistration in the transferred toner image can be suppressed.

  FIG. 1 and FIG. 3 are schematic diagrams respectively showing specific examples of a tandem color image forming apparatus, FIG. 1 shows a direct transfer type image forming apparatus, and FIG. 3 shows an intermediate transfer type image forming apparatus. ing. First, the configuration of the direct transfer type color image forming apparatus shown in FIG. 1 will be described.

  The image forming apparatus shown in FIG. 1 has a plurality of image carriers 3Y, 3C, 3M, 3BK composed of drum-shaped photoconductors, and toner images of different colors are provided on the image carriers. Are formed respectively. In the illustrated example, yellow toner images, cyan toner images, and magenta toner images are formed on the surfaces of three image carriers 3Y, 3C, and 3M, respectively, and black toner is formed on the image carrier 3BK. An image is formed. The image carriers 3Y to 3BK are arranged in parallel with each other at a predetermined interval. A recording medium conveyance belt 4 composed of an endless belt is disposed opposite to the image carriers 3Y to 3BK. The recording medium conveyance belt 4 is wound around a plurality of support rollers 5, 6, and 7 in the direction of arrow A. Driven by driving.

  Since the configuration for forming the toner image on each of the image carriers 3Y to 3BK is substantially the same, only the configuration for forming the toner image on the image carrier 3Y will be described. The image carrier 3Y is rotationally driven counterclockwise in FIG. 1, and at this time, the surface of the image carrier 3Y is charged to a predetermined polarity by the charging device 9. Next, the charging surface is irradiated with writing light (laser light L in the illustrated example) emitted from the exposure apparatus 10, thereby forming an electrostatic latent image on the image carrier 3 Y, and developing the electrostatic latent image. The image is visualized as a yellow toner image by the device 11. The illustrated developing device 11 has a developing roller 8 to which a developing bias is applied, and the electrostatic latent image is visualized by a dry developer carried on the developing roller 8.

  On the other hand, a recording medium P made of transfer paper, a resin film, or the like is sent out as indicated by an arrow B from a paper supply unit 15 disposed in the lower part of the main body of the image forming apparatus. Is rotated between the image carrier 3Y and the recording medium transport belt 4 traveling in the direction of the arrow A while contacting the image carrier 3Y at a predetermined timing, and is carried and transported by the recording medium transport belt 4. Is done. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the image carrier 3Y is applied to the transfer device 13 disposed substantially opposite to the image carrier 3Y with the recording medium conveyance belt 4 interposed therebetween. As a result, the yellow toner image on the image carrier 3Y is transferred onto the recording medium P. The recording medium P constitutes an example of a transfer material to which a toner image is transferred from an image carrier. The transfer residual toner which is not transferred to the recording medium P and remains on the image carrier 3Y is removed by the cleaning device 14.

  In exactly the same manner, a cyan toner image, a magenta toner image, and a black toner image are respectively formed on the other image carriers 3C, 3M, and 3BK shown in FIG. 1, and these toner images are transferred to the yellow toner image. Then, the images are sequentially transferred onto the recording medium P. The recording medium P carrying the four-color superimposed toner images in this way is separated from the recording medium conveying belt 4 and then passes through the fixing device 2. At this time, the toner image is subjected to the action of heat and pressure to the recording medium P. Fixed on top. The recording medium that has passed through the fixing device 2 is discharged to the paper discharge unit 17. What is indicated by reference numeral 16 in FIG. 1 is a belt cleaning device that removes toner adhering to the recording medium conveyance belt 4.

  As described above, the direct transfer type image forming apparatus transfers the recorded images by directly superimposing the toner images formed on the image carriers 3Y to 3BK onto the transfer material made of the recording medium P being conveyed. Configured to get.

  On the other hand, in the intermediate transfer type image forming apparatus shown in FIG. 3, a transfer material made up of the intermediate transfer body 104 is opposed to the plurality of image carriers 3Y to 3BK. A drum may be used as the intermediate transfer member. However, in the illustrated example, like the recording medium conveying belt 4 in FIG. 1, it is wound around a plurality of support rollers 5, 6, and 7 and driven in the direction of arrow A. An intermediate transfer member composed of an endless belt is used.

  In the case of the image forming apparatus shown in FIG. 3, the yellow toner image formed on the image carrier 3 </ b> Y is transferred to the surface of the intermediate transfer body 104 driven to run in the direction of arrow A by the action of the transfer device 13. Is done. The transfer residual toner adhering to the image carrier 3Y after the toner image transfer is removed by the cleaning device 14. The cyan toner image, the magenta toner image, and the black toner image respectively formed on the other image carriers 3C, 3M, and 3BK in the same manner are sequentially superimposed on the surface of the intermediate transfer member 104 on which the yellow toner image is transferred. Transcribed. In this way, a four-color superimposed toner image is formed on the intermediate transfer member 104.

  In the image forming apparatus shown in FIG. 3, the secondary transfer device 20 is disposed opposite the support roller 7 with the intermediate transfer member 104 interposed therebetween, and the transfer paper or resin film sent out from the paper supply unit 15. As shown by the arrow C, the recording medium P composed of the recording roller P is fed between the secondary transfer device 20 and the intermediate transfer member 104 at a predetermined timing by the rotation of the registration roller pair 12. In this way, when the recording medium P passes through the secondary transfer device 20, the superimposed toner images on the intermediate transfer body 104 are collectively transferred onto the recording medium P by the action of the transfer device 20. The transfer residual toner adhering to the surface of the intermediate transfer member 104 after the toner image transfer is removed by the belt cleaning device 16.

  The recording medium P to which the toner image has been transferred is conveyed by the recording medium conveying device 40 and passes through the fixing device 2. At this time, the transferred toner image is fixed on the recording medium P by the action of heat and pressure. . The recording medium P that has passed through the fixing device 2 is discharged to the paper discharge unit 17. In FIG. 3, the secondary transfer device 20 composed of a transfer roller is used, but a secondary transfer device having a transport belt for transporting the recording medium can also be used. Other configurations of the image forming apparatus shown in FIG. 3 are the same as those of the image forming apparatus shown in FIG. 1, and the same or corresponding parts are denoted by the same reference numerals as those in FIG.

  As described above, the intermediate transfer type image forming apparatus is configured to obtain a recorded image by transferring the toner image formed on each of the image carriers 3Y to 3BK on a transfer material including the intermediate transfer body 104. Has been.

  As described above, the color mode for forming a color image on the recording medium P by the image forming apparatus shown in FIGS. 1 and 3 has been described. In the image forming apparatus shown in FIGS. It is also possible to select a monochrome mode for forming a black monochrome image on a recording medium. In the monochrome mode, the recording medium conveyance belt 4 shown in FIG. 1 and the intermediate transfer member 104 shown in FIG. 3 are separated from the image carriers 3Y, 3C, and 3M on which chromatic toner images are formed, and the black toner image is formed. It abuts only on the image carrier 3BK to be formed. In addition, the image carriers 3Y, 3C, 3M other than the image carrier 3BK do not rotate, and only the image carrier 3BK is driven to rotate, and the black toner is formed on the image carrier 3BK in the same manner as described above. An image is formed.

  In this case, in the case of the image forming apparatus shown in FIG. 1, the black toner image is directly transferred to the recording medium P fed from the paper feeding unit 15 and fed by the registration roller pair 12 at a predetermined timing. Is done. This recording medium is carried and conveyed on a recording medium conveyance belt 4 that rotates in the direction of arrow A. On the other hand, in the case of the image forming apparatus shown in FIG. 3, the black toner image formed on the image carrier 3BK is transferred to the intermediate transfer member 104 running in the direction of arrow A, and then the toner image is fed to the paper feeding unit 15. Is transferred to the recording medium P fed from the recording medium P. 1 and 3, when the recording medium P to which the black toner image is transferred passes through the fixing device 2, the black toner image is fixed on the recording medium P, and the recording medium P Is discharged to the paper discharge unit 17.

  2 and 4 omit illustration of process equipment for forming toner images on the image carriers 3Y to 3BK of the image forming apparatus shown in FIGS. 1 and 3, and the image carriers 3Y to 3BK are not illustrated. It is the perspective view which clarified the structure of the drive system to drive. As shown in these drawings, each of the image carriers 3Y to 3BK is fixedly supported by rotation shafts 18Y, 18C, 18M, and 18BK that are concentric with these image carriers, and is supported by each of the rotation shafts 18Y, 18C, 18M, and 18BK. The gears 19Y, 19C, 19M, and 19BK are fixed respectively. These gears 19Y to 19BK are arranged concentrically with respect to the respective image carriers 3Y to 3BK, and rotate to the respective image carriers 3Y to 3BK so as to rotate together with the respective image carriers 3Y to 3BK. The shafts 18Y to 18BK are connected to each other. The image carriers 3Y to 3BK are not rotatable relative to the rotation shafts 18Y to 18BK, but are assembled to the rotation shafts 18Y to 18BK so as to be detachable in the axial direction of the rotation shafts 18Y to 18BK. The gears 19Y to 19BK can be directly fixedly connected to the image carriers 3Y to 3BK without the rotation shafts 18Y to 18BK.

  Each of the gears 19Y to 19BK is rotationally driven as will be described later, whereby the image carriers 3Y to 3BK are rotated counterclockwise in FIGS. 1 and 3, and the image carriers 3Y to 3Y are to be rotated as described above. A toner image is formed on the peripheral surface of 3BK. In the color mode, the image carriers 3Y, 3C, 3M on which chromatic toner images are formed and the gears 19Y, 19C, 19M connected thereto are stopped, and only the image carrier 3BK and the gear 19BK connected thereto. Rotates.

  Here, in the image forming apparatus shown in FIGS. 1 to 4, the image carriers 3Y, 3C, and 3M on which the chromatic toner images are formed are referred to as color image carriers as necessary, and the black toner images are formed. The formed image carrier 3BK will be referred to as a black image carrier as necessary. Further, the gears 19Y, 19C, and 19M connected to the color image carriers 3Y, 3C, and 3M are replaced with the color gear and the gear 19BK connected to the black image carrier 3BK as necessary. It will be called a gear for use. In the illustrated example, three color image carriers 3Y, 3C, and 3M are provided. However, at least two color image carriers are provided, and at least three colors are provided in the color mode. An image is formed.

  As described above, the image forming apparatus of the present example includes a plurality of color image carriers 3Y, 3C, and 3M on which chromatic toner images are formed, and one black image carrier 3BK on which black toner images are formed. The color image carriers 3Y, 3C, and 3M are arranged concentrically with the color image carriers 3Y, 3C, and 3M and rotate together with the color image carriers 3Y, 3C, and 3M. The color gears 19Y, 19C, and 19M connected to the black image carrier 3BK are concentrically arranged and connected to the black image carrier so as to rotate together with the black image carrier 3BK. And a black gear 19BK. Then, chromatic toner images of different colors are formed on the color image carriers 3Y, 3C, 3M, which are rotationally driven together with the color gears 19Y, 19C, 19M, respectively, and are rotationally driven together with the black gear 19BK. A black toner image is formed on the black image carrier 3BK, and the chromatic toner image and the black toner image are superimposed on a transfer material (the recording medium P in the case of FIG. 1 and the intermediate transfer member 104 in the case of FIG. 3). Color mode for obtaining a color image by transferring the color, and the color gears 19Y, 19C, 19M and the color image carriers 3Y, 3C, 3M are stopped, and the black image carrier 3BK is rotated together with the black gear 19BK. A monochrome mode in which a black toner image is formed and a black image is obtained by transferring only the black toner image onto a transfer material can be selected.

  The black gear 19BK and the color gears 19Y, 19C, 19M shown in FIGS. 2 and 4 have the same radius and the same number of teeth, and are made of, for example, resin or metal. At this time, in particular, when these gears are made of resin, it is inevitable that the gears are slightly decentered. As a result, the gears are transferred to the recording medium P shown in FIG. 1 or the intermediate transfer member 104 shown in FIG. There is a risk of color misregistration occurring in the superimposed toner images.

  Therefore, in the image forming apparatus shown in FIGS. 1 to 4, the color gears 19Y and 19C are prevented so that color misregistration does not occur in the superimposed toner image transferred to the transfer material in the color mode, as in the prior art. , 19M and the black gear 19BK are configured to rotate while maintaining a predetermined phase relationship.

  FIG. 5 is a diagram illustrating an example of the configuration of the image forming apparatus illustrated in FIGS. 1 and 2. Here, it is assumed that the distance between the transfer positions at which the toner images are transferred from the image carriers 3Y, 3C, 3M, 3BK to the recording medium P is LA. A certain position of the outer peripheral surface in the circumferential direction of each of the image carriers 3Y to 3BK and the circumferential position of each of the color gears 19Y, 19C, 19M and the black gear 19BK corresponding thereto are represented by X. A certain position X of each of the color gears 19Y, 19C, 19M and the black gear 19BK is, for example, a circumferential position where each of the gears is eccentric to the maximum with respect to the rotation center. This position X is referred to as a reference position for convenience.

  In the state shown in FIG. 5, the reference position X of the image carrier 3Y where the yellow toner image is formed is at the transfer position, and the yellow toner image on the image carrier 3Y is transferred to the recording medium P. At this time, the reference position X of the image carrier 3C adjacent to the image carrier 3Y is at a position away from the transfer position by LA on the upstream side in the rotation direction of the image carrier 3C. The reference position X is separated by 2 × LA upstream from the transfer position. Similarly, the image carrier 3BK is separated by 3 × LA from the transfer position. The relative positions of the reference positions of the color gears 19Y, 19C, 19M and the black gear 19BK in the rotational direction are determined so as to have such a positional relationship. Accordingly, even when the gears 19Y to 19BK are slightly decentered, color misregistration can be prevented from occurring in the superimposed toner image transferred onto the recording medium in the color mode. The mounting angle position of the color gears 19Y, 19C, 19M and the black gear 19BK or the circumferential position thereof are set so as to prevent color shift from occurring in the completed color image due to the eccentricity of each gear. It is. The image forming apparatus shown in FIGS. 3 and 4 has the same configuration, and is transferred from each image carrier to the intermediate transfer member 104 by the eccentricity of the color gears 19Y, 19C, 19M and the black gear 19BK. It is possible to prevent color misregistration from occurring in the superimposed toner image.

  However, in the monochrome mode, the color gears 19Y, 19C, 19M and the color image carriers 3Y, 3C, 3M are stopped, and only the black gear 19BK and the black image carrier 3BK are rotated. If the color mode image forming operation is performed as it is, color misregistration may occur in the superimposed toner image transferred onto the transfer material. Therefore, the image forming apparatus of the present example is configured so that the above-described phase relationship can be easily obtained when switching from the monochrome mode to the color mode with a simple configuration as described below.

  First, as shown in FIGS. 2, 4 and 6, the intermediate gear 21 is engaged with the color gears 19Y and 19C respectively connected to the two color image carriers 3Y and 3C adjacent to each other. The gears 19Y and 19C are drivingly connected by the intermediate gear 21. Similarly, the color gears 19 </ b> C and 19 </ b> M adjacent to each other are drivingly connected by another intermediate gear 22. Further, the input side idler gear 23 meshes with the black gear 19BK, and the output side idler gear 24 meshes with the color gear 19M adjacent to the black gear 19BK.

  As described above, the image forming apparatus of this example is engaged with the color gears 19Y, 19C, and 19M connected to the color image carriers 3Y, 3C, and 3M adjacent to each other to drive and connect both the color gears. Intermediate gears 21 and 22, an input side idler gear 23 meshing with the black gear 19BK connected to the black image carrier 3BK, and a color image carrier 3M located adjacent to the black image carrier 3BK. And an output side idler gear 24 that meshes with the color gear 19M.

  As shown in FIGS. 7 and 8, the input-side idler gear 23 is fixed concentrically to the connecting shaft 25, and the output-side idler gear 24 is connected to the connecting shaft 25 via an electromagnetic clutch 26 which is an example of a switching means. It is fitted concentrically.

  Further, as shown in FIG. 6, the black gear 19BK is engaged with the output gear 27 of the drive motor M, and the black gear 19BK is rotationally driven by the drive motor M. All the image carriers 3Y to 3BK are rotationally driven by this single drive motor M. The output gear 27 of the drive motor M may be engaged with the input side idler gear 23 and the input side idler gear 23 may be rotationally driven by the motor M. Thus, the image forming apparatus of this example includes the drive motor M that rotationally drives the black gear 19BK or the input-side idler gear 23.

  When the color mode is selected, the electromagnetic clutch 26, which is an example of the switching means, is turned on, whereby the output-side idler gear 24 and the connecting shaft 25 are integrally connected. When the drive motor M starts operating in this state, the rotation of the output gear 27 is transmitted to the black gear 19BK, and the black image carrier 3BK rotates counterclockwise in FIGS. In addition, the rotation of the black gear 19BK is transmitted to the color gear 19M via the input-side idler gear 23, the connecting shaft 25, and the output-side idler gear 24, whereby the image carrier 3M is rotated counterclockwise in FIGS. Rotate. Similarly, the rotation of the color gear 19M is transmitted to the color gear 19C via the intermediate gear 22, and the rotation is transmitted to the color gear 19Y via the other intermediate gear 21, so that each image carrier 3C, 3Y rotates counterclockwise in FIGS. As a result, the toner images of the respective colors can be formed on the image carriers 3Y to 3BK as described above.

  On the other hand, when the monochrome mode is selected, the electromagnetic clutch 26, which is an example of the switching means, is turned off, thereby releasing the connection between the output idler gear 24 and the connecting shaft 25 so that they can freely rotate relative to each other. Become. Therefore, by the rotation of the drive motor M, the black gear 19BK, the black image carrier 3BK, the input side idler gear 23, and the connecting shaft 25 rotate in the same manner as in the color mode, but the connecting shaft 25 rotates. It is not transmitted to the output side idler gear 24. For this reason, the color gears 19Y, 19C, and 19M and the color image carriers 3Y, 3C, and 3M do not rotate, and a black toner image is formed only on the black image carrier 3BK.

  As described above, the switching means connects the input side idler gear and the output side idler gear so that the rotation of the input side idler gear is transmitted to the output side idler gear in the color mode, and the rotation of the input side idler gear is output in the monochrome mode. The input idler gear and the output idler gear are disconnected so that they are not transmitted to the side idler gear.

  Further, as shown in FIGS. 7 and 8, a disk 28 is fixed to the input side idler gear 23, and a mark S is formed on the disk 28. In addition, a sensor 29 is disposed opposite to the disk 28. As the sensor 29, for example, a photosensor having a light emitting element and a light receiving element can be used.

  When switching from the monochrome mode to the color mode, the drive motor M is operated prior to this switching, and the rotation of the output gear 27 is transmitted to the input-side idler gear 23 via the black gear 19BK. At this time, since the electromagnetic clutch 26 is turned off, the rotation of the input side idler gear 23 is not transmitted to the output side idler gear 24, and the output side idler gear 24 remains stopped. When the sensor 29 detects the mark S on the disk 28, the electromagnetic clutch 26 is turned on based on the detection signal to integrally connect the output side idler gear 24 and the connecting shaft 25 to the input side idler gear 23. The input side idler gears 23 are drivingly connected to each other. At this time, the predetermined phase relationship between the black gear 19BK and the color gears 19Y, 19C, and 19M is obtained. In order to obtain such a phase relationship, the positions of the sensor 29 and the mark S are determined in advance.

  As described above, in the image forming apparatus of this example, prior to switching from the monochrome mode to the color mode, the input-side idler gear 23 and the output-side idler gear 24 are black and the color gears 19Y, 19C, 19M. The input gear 19BK is rotated to a predetermined position where a predetermined phase relationship is obtained, and then the rotation of the input-side idler gear 23 is transmitted to the output-side idler gear 24 by an electromagnetic clutch 26 which is an example of a switching means. The idler gear 23 and the output side idler gear 24 are connected. Thus, a predetermined phase relationship between the gears 19Y to 19BK can be obtained with a simple configuration.

  In the image forming apparatus of this example, since the electromagnetic clutch 26 is used as the switching means, the input-side idler gear 23 and the output-side idler gear 24 can be connected and released accurately and quickly.

  Further, in the illustrated example, a mark S is given to a disk 28 which is an example of a member that rotates integrally with the input-side idler gear 23, and this is detected by the sensor 29. However, the mark is directly attached to the input-side idler gear 23. May be. A sensor 29 for detecting a mark S attached to the input side idler gear 23 or a member that rotates integrally with the input side idler gear 23 is provided. Prior to switching from the monochrome mode to the color mode, the sensor 29 displays the mark S. Based on the detection signal at the time of detection, the switching means is operated to connect the input side idler gear 23 and the output side idler gear 24.

  In the illustrated example, the output gear 27 of the drive motor M is directly meshed with the input-side idler gear 23 or the black gear 19BK, and no other gear is interposed between the gears 23 and 19BK and the output gear 27. . Therefore, the number of gears to be used can be minimized, the cost of the image forming apparatus can be reduced, and the uneven rotation of the image carriers 3Y to 3BK, which is generated by increasing the number of gears, can be prevented. it can.

  Further, the number of teeth of the color gears 19Y, 19C, 19M and the black gear 19BK is equal, and the diameters of the image carriers 3Y to 3BK are set to be equal, and all the image carriers 3Y to 3BK are at the same speed. In this case, if the input side idler gear 23, the output side idler gear 24, and the intermediate gears 21, 22 have the same number of teeth, they are the same as the gears 23, 24, 21, 22 Therefore, the cost of the image forming apparatus can be reduced.

  When the number of teeth of the input side idler gear 23, the output side idler gear 24, and the intermediate gears 21 and 22 is an integral multiple of the number of teeth of the output gear 27 of the drive motor M, the input side idler gear 23 and the output side idler gear 24 are used. In addition, one rotation cycle of the intermediate gears 21 and 22 can be an integral multiple of one rotation cycle of the output gear 27. As a result, even if color misregistration occurs in the superimposed toner image on the transfer material due to the eccentricity of these gears 27, 23, 24, 21, 22, the same color misregistration appears periodically, and the color misregistration occurrence state is Fluctuation can be prevented.

  Of the black gear 19BK and the input side idler gear 23, the number of teeth of the gear with the larger number of teeth is an integral multiple of the number of teeth of the gear with the smaller number of teeth, and the output side idler gear 24, Of the color gear 19M meshing with the output side idler gear 24, the number of teeth of the gear with the larger number of teeth is an integral multiple of the number of teeth of the gear with the smaller number of teeth, and the color gear 19Y, Even if the number of teeth of the gear with the larger number of teeth of 19C, 19M and the intermediate gears 20, 21 meshing with the color gear is an integral multiple of the number of teeth of the gear with the smaller number of teeth, In the same manner as described above, it is possible to prevent occurrence of variation in color misregistration.

  As shown in FIG. 6, the black gear 19BK and the input-side idler gear 23 constitute a gear pair that meshes with each other. At this time, the thickness T1 of the black gear 19BK is changed to the thickness T2 of the input-side idler gear 23. When the input side idler gear 23 is meshed with the thinner black gear 19BK within the thickness range of the thicker input side idler gear 23, the input side idler gear 23 is manufactured. By reducing the manufacturing accuracy in order to reduce the cost, even if a burr or chipping occurs at the end of the input side idler gear 23, rotation can be correctly transmitted from the black gear 19BK to the input side idler gear 23. Conversely, if the thickness of the black gear 19BK is set larger than the thickness of the input idler gear 23 so that the input idler gear 23 is within the thickness range of the black gear 19BK, the black gear 19BK is manufactured. The accuracy can be lowered and the cost can be reduced. The same applies to a gear pair composed of the color gear 19M and the output side idler gear 24, a gear pair composed of the color gear and the intermediate gear, and the like. In short, of the gear pairs composed of two gears meshing with each other, the thickness of one gear of at least one gear pair is formed thinner than the thickness of the other gear, and the range of the thickness of one gear is the other gear. By configuring so as to be engaged with the other gear in a state where it is housed inside, the manufacturing cost of the image forming apparatus can be reduced.

  Further, as described above, the color gears 19Y, 19C, 19M and the black gear 19BK can be made of resin, but at that time, the resin is excellent in slidability such as polyamide resin, polyacetal resin, and oil-containing resin material. Preferably, these gears are manufactured. In addition, if the color gear and the black gear are made of resin gears molded by the same mold, it is possible to suppress variations in the shapes of these gears, which are transferred onto the transfer material. Occurrence of color misregistration in the combined toner image can be more reliably suppressed.

  In the drawings, the gear teeth are not shown except for FIG. 8. However, as these gears, for example, an appropriate gear such as a spur gear or a helical gear can be adopted. it can.

1 is a partial cross-sectional schematic diagram illustrating an example of a direct transfer type image forming apparatus. FIG. 2 is a perspective view showing a drive system of the image forming apparatus shown in FIG. 1. 1 is a schematic partial cross-sectional view illustrating an example of an intermediate transfer type image forming apparatus. FIG. 4 is a perspective view showing a drive system of the image forming apparatus shown in FIG. 3. It is explanatory drawing which shows an example of the phase relationship of the gear for black and the gear for color. It is a top view of the drive system of each image carrier. It is a perspective view of an input side idler gear and an output side idler gear. It is sectional drawing of an input side idler gear and an output side idler gear.

Explanation of symbols

3Y, 3C, 3M, 3BK Image carrier 19Y, 19C, 19M Color gear 19BK Black gear 21, 22 Intermediate gear 23 Input side idler gear 24 Output side idler gear 26 Electromagnetic clutch 27 Output gear 29 Sensor M Drive motor T1, T2 Thickness

Claims (11)

A plurality of color image carriers on which chromatic color toner images are formed, one black image carrier on which black toner images are formed, concentrically arranged with respect to each color image carrier, and A color gear connected to each color image carrier so as to rotate together with the color image carrier, and a concentric arrangement with respect to the black image carrier, and rotate together with the black image carrier. In this way, a black gear connected to the black image carrier is formed, and chromatic toner images of different colors are respectively formed on the color image carriers that are rotationally driven together with the color gears. A color mode for forming a black toner image on a black image carrier that is rotationally driven together with a gear, and transferring the chromatic color toner image and the black toner image on a transfer material to obtain a color image; and the color gear; Stop the color image carrier and rotate with the black gear It is possible to select a monochrome mode in which a black toner image is formed on a moved black image carrier and only the black toner image is transferred to a transfer material to obtain a black image. In the image forming apparatus configured such that each color gear and the black gear rotate while maintaining a predetermined phase relationship so that color transfer does not occur in the transferred superimposed toner image.
An intermediate gear that meshes with the color gears connected to each of the color image carriers adjacent to each other and drives and couples both color gears, and an input-side idler gear that meshes with the black gears connected to the black image carrier. The output idler gear meshing with the color gear connected to the color image carrier positioned adjacent to the black image carrier, and the rotation of the input idler gear is transmitted to the output idler gear in the color mode. A switching means for connecting the input side idler gear and the output side idler gear so that the rotation of the input side idler gear is not transmitted to the output side idler gear in the monochrome mode. A drive motor that rotationally drives the input gear or the input side idler gear, and from the monochrome mode Prior to switching to the error mode, the input idler gear is rotated to a predetermined position where a predetermined phase relationship between the color gear and the black gear is obtained with respect to the output idler gear, and then the input idler gear. An image forming apparatus characterized in that the input side idler gear and the output side idler gear are connected by the switching means so that the rotation of the motor is transmitted to the output side idler gear. The image forming apparatus according to claim 1, wherein an electromagnetic clutch is used as the switching unit. A sensor for detecting a mark attached to the input-side idler gear or a member that rotates integrally with the input-side idler gear is provided, and detection when the sensor detects the mark prior to switching from the monochrome mode to the color mode. The image forming apparatus according to claim 1, wherein the switching unit is operated based on a signal to connect the input-side idler gear and the output-side idler gear. The image forming apparatus according to claim 1, wherein an output gear of the drive motor is directly meshed with the input-side idler gear or the black gear. The image forming apparatus according to claim 1, wherein the number of teeth of the input side idler gear, the output side idler gear, and the intermediate gear is the same. 6. The image forming apparatus according to claim 1, wherein the number of teeth of the input side idler gear, the output side idler gear, and the intermediate gear is an integral multiple of the number of teeth of the output gear of the drive motor. The number of teeth of the gear with the larger number of teeth of the black gear and the input side idler gear is an integral multiple of the number of teeth of the gear with the smaller number of teeth. The image forming apparatus described. 2. The number of teeth of the gear having the larger number of teeth among the output side idler gear and the color gear meshing with the output side idler gear is an integral multiple of the number of teeth of the gear having the smaller number of teeth. 8. The image forming apparatus according to any one of 7 to 7. The number of teeth of the gear having the larger number of teeth among the color gear and the intermediate gear meshing with the color gear is an integral multiple of the number of teeth of the gear having the smaller number of teeth. The image forming apparatus according to claim 8. Of the gear pairs composed of two gears meshing with each other, the thickness of one gear of at least one gear pair is formed thinner than the thickness of the other gear, and one gear is within the thickness range of the other gear. The image forming apparatus according to claim 1, wherein the image forming apparatus is meshed with the other gear in a closed state. The image forming apparatus according to claim 1, wherein the color gear and the black gear are made of a resin gear formed by the same mold.

Images