JP2005128161A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of color slurring on the toner image transferred to the recording medium caused by ribs of a gear for color and a gear for black, in an image forming apparatus which is provided with a photoreceptor drum for color on which a chromatic color toner image is formed, the gear for color concentrically coupled with the photoreceptor drum for color, a photoreceptor drum for black on which a black toner image is formed and the gear for black concentrically coupled with the photoreceptor drum for black, where the gear for color and the gear for black are composed of molding equipped with a rib extended radially and where the toner images formed on the photoreceptor drums are transferred to a recording medium at a transfer position. <P>SOLUTION: The image forming apparatus is constituted to satisfy L≈n(πD/k) (n is an integer) when it is assumed that the toner image transfer distance of photoreceptor drums for color 3Y, 3M and 3C and a photoreceptor drum for black 3BK adjacent to each other is L, the number of the ribs provided on the gear for color and the gear for black respectively is (k) and the diameter of the photoreceptor drum is D. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a plurality of color photosensitive drums on which chromatic toner images of different colors are respectively formed, one black photosensitive drum on which a black toner image is formed, and each color photosensitive drum in a concentric manner. The color gear that rotates together with the photosensitive drum for each color, the black gear that rotates concentrically with the photosensitive drum for black, and the color gear that rotates together with the photosensitive drum for black. Therefore, a color drive gear that meshes with each color gear and a black drive gear that meshes with the black gear in order to rotationally drive the black gear, and rotates the color photosensitive drum and the black photosensitive drum. A color mode for driving to form a chromatic color toner image and a black toner image on the color photosensitive drum and the black photosensitive drum, respectively, and transferring the respective toner images on a transfer material to obtain a color image; Select the monochrome mode that stops the color photosensitive drum, rotates the black photosensitive drum to form a black toner image on the black photosensitive drum, and transfers the black toner image to a transfer material to obtain a black image. The plurality of color gears and black gears are related to an image forming apparatus comprising a molded product having the same number of radially extending ribs.

  An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile, or a complex machine thereof is also called a tandem color image forming apparatus because a plurality of photosensitive drums are arranged side by side. . Such an image forming apparatus includes a direct transfer type image forming apparatus that directly superimposes and transfers a toner image of each color formed on each photosensitive drum onto a transfer material made of a recording medium, and a toner image formed on each photosensitive drum. The image forming apparatus can be divided into an intermediate transfer type image forming apparatus that transfers the superimposed toner image onto a recording medium by transferring the image onto a transfer material made of an intermediate transfer member.

  In any type of image forming apparatus, since the color photosensitive drum is stopped in the monochrome mode, the burden on the process equipment for forming the toner image on each color photosensitive drum can be reduced, and the life thereof is extended. It is possible.

  By the way, if the color gear and the black gear, which are arranged concentrically with each photosensitive drum and are rotationally driven together with the photosensitive drum, are formed of a molded product having ribs extending radially, the shrinkage immediately after the molding is performed. Due to the difference, the radius of the portion where the rib exists is smaller than the radius of the other portion. For this reason, the radius of the color gear and the black gear is not constant in the circumferential direction, and a portion with a large radius and a portion with a small radius are formed. For this reason, even if the color gear and the black gear are rotationally driven by the color drive gear and the black drive gear that rotate at equal angular speeds, speed variations occur in the color gear and the black gear, which causes transfer. The toner image transferred to the material is inevitably suffered from the disadvantage that color misregistration occurs and the image quality deteriorates.

  The present invention has been made on the basis of the above-described novel recognition, and an object of the present invention is to generate color misregistration of a toner image due to the ribs of the color gear and the black gear with a simple configuration. An object of the present invention is to provide an image forming apparatus of the type described at the beginning which can be effectively suppressed.

In order to achieve the above object, according to the present invention, in the image forming apparatus of the type described at the beginning, when the black drive gear meshes with the minimum diameter portion of the black gear, the color drive gear is also a color gear. The positions of the black driving gear and the color driving gear are set so as to mesh with the almost minimum diameter portion, and the distance between the transfer positions of the color photosensitive drum and the black photosensitive drum adjacent to each other is set to L. And k is the number of ribs provided on the black gear, D is the diameter of the color photosensitive drum and the black photosensitive drum, and n is an integer.
L≈n (πD / k)
L, k, and D are set so as to satisfy the conditions, and in the color mode, the position of the rib in the circumferential direction of the color gear is substantially the same as the position of the rib in the circumferential direction of the black gear. An image forming apparatus is proposed in which a gear and a black gear are arranged (claim 1).

  At this time, the plurality of color gears are assembled so that the positions of the ribs in the circumferential direction substantially coincide with each other, and when the mode is switched from the monochrome mode to the color mode, before the color mode is executed, It is advantageous if a control means is provided for making the position of the rib in the circumferential direction of the color gear substantially coincide with the position of the rib in the circumferential direction of the collar gear.

  The image forming apparatus according to claim 2, wherein the control unit includes a color sensor that detects a rib of one color gear, and a black sensor that detects a rib of the black gear, When the color sensor detects a rotating color gear rib, the color gear is stopped. When the black sensor detects a rotating black gear rib, the black gear is stopped. It is advantageous if it is configured as described above (claim 3).

  According to the present invention, it is possible to effectively suppress the occurrence of color misregistration in the toner image due to the ribs of the color gear and the black gear.

  FIG. 1 is a schematic view showing an example of an image forming apparatus of a tandem type and a direct transfer type. The image forming apparatus shown here has a plurality of photosensitive drums 3Y, 3M, 3C, 3BK arranged in parallel to each other in the main body 1. Here, four photosensitive drums are provided, and chromatic color toner images of yellow toner image, magenta toner image, and cyan toner image are respectively formed on the peripheral surfaces of three photosensitive drums 3Y, 3M, and 3C. A black toner image is formed on the photosensitive drum 3BK. The diameters of the photosensitive drums 3Y to 3BK are all set equal. A recording medium conveyance belt 4 is disposed to face the photosensitive drums 3Y to 3BK. The recording medium conveyance belt 4 is wound around a plurality of support rollers 5, 6, and 7 and is driven to run in the direction of arrow A.

  Since the operation of forming a toner image on each of the photosensitive drums 3Y, 3M, 3C, and 3BK is substantially the same as that of the configuration, only the configuration of forming a toner image on the peripheral surface of the photosensitive drum 3Y will be described here. To do. The photosensitive drum 3Y is driven to rotate counterclockwise in FIG. 1, and at this time, the surface of the photosensitive drum is charged to a predetermined polarity by the charging device 9. Next, the charged surface is irradiated with light-modulated writing light (laser light L in the example shown) emitted from the exposure apparatus 10. As a result, an electrostatic latent image is formed on the photosensitive drum 3Y, and the electrostatic latent image is visualized as a yellow toner image by the developing device 11.

  On the other hand, a recording medium P made of transfer paper or a resin film is sent out in a direction indicated by an arrow B from a paper feeding unit 15 arranged at the lower part of the image forming apparatus main body 1. The roller pair 12 is rotated at a predetermined timing between the photosensitive drum 3Y and the recording medium conveyance belt 4 in contact with the photosensitive drum 3Y, and is carried and conveyed by the recording medium conveyance belt 4. At this time, the yellow toner image on the photosensitive drum 3 </ b> Y is transferred onto the recording medium P by the action of the transfer device 13 disposed substantially opposite to the photosensitive drum 3 </ b> Y with the recording medium conveyance belt 4 interposed therebetween. The residual transfer toner that is not transferred to the recording medium P and remains on the photosensitive drum 3Y is removed by the cleaning device 14. The recording medium P constitutes an example of a transfer material to which a toner image is transferred from a photosensitive drum.

  In exactly the same manner, magenta toner images, cyan toner images, and black toner images are respectively formed on the other photosensitive drums 3M, 3C, and 3BK, and these toner images are formed on the recording medium P on which the yellow toner image is transferred. The images are transferred one after another. The recording medium P carrying the four-color unfixed toner images in this way leaves the recording medium conveyance belt 4 and then passes through the fixing device 2. At this time, the toner image is recorded by the action of heat and pressure. Fixed on P. The recording medium that has passed through the fixing device 2 is discharged onto the paper discharge unit 17. The toner adhering to the recording medium conveyance belt 4 is removed by a belt cleaning device 16. In this way, a recording medium on which a color image is formed can be obtained.

  Although the above operation is a color mode for forming a color image on a recording medium, the illustrated image forming apparatus can select a monochrome mode for forming a black monochrome image on the recording medium in addition to this color mode. . In the monochrome mode, the recording medium conveyance belt 4 is separated from the photosensitive drums 3Y, 3M, and 3C on which the chromatic toner images are formed and contacts only with the photosensitive drum 3BK on which the black toner images are formed. In addition, the photosensitive drums 3Y, 3M, 3C other than the photosensitive drum 3BK do not rotate, and only the photosensitive drum 3BK is rotationally driven, and a black toner image is formed on the photosensitive drum 3BK in the same manner as described above. The The black toner image is fed from the paper feeding unit 15, fed at a predetermined timing by the registration roller pair 12, and is carried on the recording medium conveyance belt 4 that rotates in the direction of arrow A and is conveyed. Is transcribed. This recording medium also passes through the fixing device 2. At this time, the black toner image is fixed on the recording medium P, and the recording medium P is discharged to the paper discharge unit 17.

  Here, when it is necessary to identify each photosensitive drum, the photosensitive drum 3BK on which the black toner image is formed is referred to as a black photosensitive drum, and a yellow toner image, a magenta toner image, and a cyan toner image are respectively formed. The photosensitive drums 3Y to 3C are referred to as a yellow photosensitive drum, a magenta photosensitive drum, and a cyan photosensitive drum, respectively. Furthermore, when a plurality of photosensitive drums 3Y, 3M, and 3C on which chromatic toner images are formed are collectively referred to as color photosensitive drums. As can be seen from the above description, the image forming apparatus of this example forms a plurality of color photosensitive drums 3Y, 3M, and 3C on which chromatic toner images of different colors are formed, and a black toner image. One black photosensitive drum 3BK is provided.

  FIG. 2 is an explanatory diagram showing the photosensitive drums 3Y to 3BK and a driving system for driving the photosensitive drums. FIG. 3 is a perspective view showing the black photosensitive drum 3BK and a driving system for driving the photosensitive drum 3BK. As shown in FIGS. 2 and 3, a black gear 19BK is concentrically fixed to the black photosensitive drum 3BK at the end on the back side of the support shaft 18BK that fixes and supports the black photosensitive drum 3BK. ing. Further, as shown in FIG. 2, the rear end portions of the support shafts 18Y, 18M, and 18C for fixing and supporting the other color photosensitive drums 3Y, 3M, and 3C also have the same as in the case of the black photosensitive drum 3BK. A yellow gear 19Y, a magenta gear 19M, and a cyan gear 19C are fixed concentrically with the photosensitive drums 3Y, 3M, and 3C, respectively. The support shafts 18Y, 18M, 18C, and 18BK are rotatably supported by the machine frame of the image forming apparatus main body. Also here, when the yellow gear 19Y, the magenta gear 19M and the cyan gear 19C connected to the respective color photosensitive drums 3Y, 3M, 3C are collectively referred to as color gears. The same gear is used as the color gears 19Y to 19C and the black gear 19BK, and the number of teeth and the diameter thereof are all set equal.

  As shown in FIGS. 2 and 3, the black gear 19BK meshes with the black drive gear 21BK formed of the output gear of the first motor 20, and the rotation of the first motor 20 is the same as that of the black drive gear 21BK. The black photosensitive drum 3BK is transmitted to the black photosensitive drum 3BK via the black gear 19BK and the support shaft 18BK, and rotates together with the black gear 19BK in the counterclockwise direction in FIGS. In this way, a black toner image is formed on the black photosensitive drum 3BK as described above. The magenta gear 19M and the cyan gear 19C are engaged with a color drive gear 21A composed of an output gear of the second motor 22, and the yellow gear 19Y and the magenta gear 19M are composed of an idle gear. The drive gear 21B is engaged. The rotation of the second motor 22 is transmitted to the magenta gear 19M and the cyan gear 19C via the color drive gear 21A, and the magenta photosensitive drum 3M and the cyan photosensitive drum 3C are respectively shown in FIGS. Rotating counterclockwise, a magenta toner image and a cyan toner image are formed on each peripheral surface. Further, the rotation of the magenta gear 19M is transmitted to the yellow gear 19Y via the other color drive gear 21B, whereby the yellow photosensitive drum 3Y is rotationally driven in the counterclockwise direction in FIGS. As a result, a yellow toner image is formed on the peripheral surface of the yellow photosensitive drum 3Y as described above. In the monochrome mode, only the first motor 20 of the first and second motors 20 and 22 is operated, and only the black photosensitive drum 3BK of the four photosensitive drums 3Y to 3BK is rotationally driven.

  As described above, the image forming apparatus of this example is arranged concentrically on each color photosensitive drum 3Y, 3M, 3C, and rotates with each color photosensitive drum 3Y, 3M, 3C. 19M and 19C and the black gear 19BK that is arranged concentrically with the black photosensitive drum 3BK and rotates together with the black photosensitive drum 3BK, and the respective color gears 19Y, 19M, and 19C to rotate. Color driving gears 21A, 21B meshing with the gears for black and a black driving gear 21BK meshing with the black gears 19BK in order to rotationally drive the black gear 19BK, and the color photosensitive drums 3Y, 3M. , 3C and the black photosensitive drum 3BK are rotationally driven, and the chromatic color toner image and the black toner are applied to the color photosensitive drums 3Y, 3M, 3C and the black photosensitive drum 3BK. Each color image is formed, and each toner image is transferred onto a transfer material and transferred to obtain a color image. The color photosensitive drums 3Y, 3M, and 3C are stopped, and the black photosensitive drum 3BK is rotationally driven. A monochrome mode in which a black toner image is formed on the black photosensitive drum 3BK and a black image is obtained by transferring the black toner image to a transfer material is selectable.

  Further, the plurality of color gears 19Y, 19M, 19C and the black gear 19BK are formed of molded products each having the same number of ribs 23 extending radially as shown in FIG. For example, these gears 19Y to 19BK are constituted by resin-molded gears or metal gears molded by die casting. Further, as shown in FIGS. 4 and 5, the color and black gears 19 </ b> Y to 19 </ b> BK of the present example have five ribs 23 extending radially from the center thereof, and the angle between the adjacent ribs 23. All α are set almost equal. In such a gear with ribs, the thickness of the portion 24 between the ribs 23 is thinner than the thickness in the gear axis direction of the portion where the ribs 23 are formed. The portion of the rib 23 is different from the portion 24 between the ribs 23. As a result, as shown exaggeratedly in FIG. 5, the color and black gears 19 </ b> Y to 19 </ b> BK have the smallest radius at the portion where the rib 23 is provided, and the largest in the position between the adjacent ribs 23. The radius. As described above, if the radii are different in the circumferential direction of the gear, even if the gears 19Y to 19BK are rotationally driven by the drive gears 21B, 21A, and 21BK that rotate at equal angular speeds, the gears 19Y Throughout 19BK and the photosensitive drums 3Y through 3BK, speed unevenness occurs, which may cause color misregistration in the superimposed toner images transferred onto the recording medium. FIG. 6 is a diagram for explaining that the angular velocities of the photosensitive drums 3Y to 3BK fluctuate in a cycle corresponding to the pitch of the ribs 23. In FIG. The image forming apparatus of this example employs the following configuration in order to prevent or effectively suppress the occurrence of this color misregistration.

  FIG. 7 is an explanatory view showing the arrangement of the drive gears 21A, 21B, 21BK and the ribs 23 of the respective gears 19Y to 19BK. FIG. 7 shows the gears 19Y to 19BK viewed from the same direction as FIG. The state of is shown. In FIG. 7, the photosensitive drums 3Y to 3BK and the recording medium conveyance belt 4 are indicated by a one-dot chain line.

  As can be seen from FIG. 7, when the black drive gear 21BK is engaged with the smallest diameter portion of the black gear 19BK provided with the ribs 23, the color drive gears 21A and 21B are also connected to the color gears 19M, 19C, It meshes with the smallest diameter portion where the 19Y rib 23 is provided. Since the number of teeth of each gear 19Y to 19BK, the diameter thereof, and the number of ribs 23 are all equal, the maximum diameter portion between two adjacent ribs 23 of the black gear 19BK is engaged with the black drive gear 21BK. In some cases, the collar drive gears 21A and 21B mesh with the maximum diameter portion between the two adjacent ribs 23 of the collar gears 19M, 19C, and 19Y. Thus, when the black drive gear 21BK is engaged with the minimum diameter portion of the black gear 19BK, the color drive gears 21A, 21B are also engaged with the substantially minimum diameter portion of the color gears 19M, 19C, 19Y. The positions of the black drive gear 21BK and the color drive gears 21A and 21B are set. This configuration is the first configuration.

Next, the positions at which the toner images are transferred from the photosensitive drums 3Y to 3BK to the recording medium P will be referred to as transfer positions, and the respective transfer positions are indicated by reference numeral T in FIGS. Further, the distance between the color photosensitive drums 3Y, 3M, 3C adjacent to each other and the transfer position T of the black photosensitive drum 3BK is L, and the color gears 19Y, 19M, 19C and the black gear 19BK are respectively provided. When the number of ribs is k, the diameters of the color photosensitive drums 3Y, 3M, and 3C and the black photosensitive drum 3BK are D and n are integers,
L≈n (πD / k)
L, k, and D are set so as to satisfy the above. This configuration is the second configuration. More specifically, since the number k of the ribs 23 of the illustrated gears 19Y to 19BK is 5, if the diameter D of the photosensitive drum is 40 mm and n is 4, the transfer distance L is about 100. 5 mm.

  Further, in the image forming apparatus of this example, as can be seen from FIG. 7, in the color mode, the positions of the ribs 23 in the circumferential direction of the color gears 19Y, 19M, 19C and the ribs 23 in the circumferential direction of the black gear 19BK. The color gears 19Y, 19M, and 19C and the black gear 19BK are disposed so that the positions of the black color and the black color 19BK substantially coincide with each other. The arrangement state of the ribs 23 of all the gears 19Y, 19M, 19C, 19BK is the same. That is, as shown in FIG. 7, when the tip of one rib 23 of the black gear 19BK is at the transfer position T, the tip of one rib of all the color gears 19Y, 19M, 19C is also transferred to the transfer position T. It is in. This configuration is a third configuration.

  By adopting the above-described first to third configurations, it is possible to match the speed fluctuation period caused by the ribs 23 of the respective photosensitive drums 3Y to 3BK, so that the superimposed toner images transferred onto the recording medium P can be adjusted. Color misregistration can be eliminated or suppressed to an extent that can be ignored, and the image quality can be improved. FIG. 8 is an explanatory diagram showing that the phases of the angular velocity fluctuations of the photosensitive drums 3Y to 3BK are aligned, thereby preventing the occurrence of color misregistration due to the angular velocity fluctuations of the photosensitive drums. In FIG. 8, Y, M, C, and BK indicate angular velocities of the photosensitive drums 3Y, 3M, 3C, and 3BK, respectively.

  In the second configuration described above, if n is an integer, the color shift of the superimposed toner image can be minimized, and conversely, if n is “integer + 0.5”, the color shift is the worst. Become. Therefore, even if n is not an integer, color misregistration can be reduced as long as it is about “integer ± 0.1”.

  By the way, the plurality of collar gears 19Y, 19M, and 19C are assembled in advance to the support shafts 18Y, 18M, and 18C so that the positions of the ribs 23 in the circumferential direction substantially coincide as shown in FIG. Yes. Therefore, no matter how the gears 19Y, 19M, and 19C rotate, the phase states of the ribs 23 always coincide with each other and never change. However, the color photosensitive drums 3Y, 3M, and 3C do not rotate in the monochrome mode, and only the black photosensitive drum 3BK rotates. Therefore, if the color mode is executed as it is after performing the monochrome mode, the color mode is changed. The color image forming operation may be performed with the positional relationship between the ribs 23 of the gears 19Y, 19M, and 19C and the ribs 23 of the black gear 19BK being out of order, and color misregistration may occur. Therefore, in the image forming apparatus of this example, when the mode is switched from the monochrome mode to the color mode, the position of the rib 23 in the circumferential direction of the black gear 19BK is changed to the color gear 19Y before the execution of the color mode. , 19M, 19C is provided with a control means that substantially matches the position of the rib 23 in the circumferential direction. A specific configuration example will be described below.

  2, 3, and 7, a black sensor 25 </ b> A composed of a light transmission type photosensor is attached to the machine frame of the image forming apparatus main body, and the light emitting element and the light receiving element of the black sensor 25 </ b> A. Is positioned with the black gear 19BK interposed therebetween. Similarly, as shown in FIGS. 2 and 7, the machine frame of the main body of the image forming apparatus is provided with a color sensor 25B composed of a light transmission type photosensor, and the light emitting element and the light receiving element of the sensor 25B are for color. It is located with the gear 19Y in between. The positions of the black sensor 25A and the color sensor 25B in the circumferential direction of the gears 19BK and 19Y are the same. Further, in FIG. 7, the sensors 25A and 25B are indicated by alternate long and short dash lines.

  Here, if the gears 19Y and 19BK are made of, for example, white polyacetal, the ribs 23 of the gears 19BK and 19Y are positioned between the light emitting elements and the light receiving elements of the sensors 25A and 25B. Since the thickness is large, the light emitted from the light emitting element does not enter the light receiving element. When the portion 24 without the ribs 23 of the gears 19BK and 19Y is located between the light emitting element and the light receiving element, the plate thickness of this portion is thin, so that the light emitted from the light emitting element is transmitted through this portion and is transmitted to the light receiving element. Incident. For this reason, the ribs 23 of the gears 19BK and 19Y can be detected by the sensors 25A and 25B. As the black sensor 25 </ b> A and the color sensor 25 </ b> B, a light-reflective photosensor or the like can be used.

  When an image forming operation is performed in the color mode, the first motor 20 is operated to rotate the black gear 19BK in the counterclockwise direction in FIG. 2 before starting the operation (S1 in FIG. 9). Next, when the black sensor 25A detects the rib 23 of the black gear 19BK (S2 in FIG. 9), the first motor 20 is stopped (S3 in FIG. 9). Subsequently, the second motor 22 is operated to rotationally drive the color photosensitive drums 3Y, 3M, 3C (S4 in FIG. 9), and when the color sensor 25B detects the rib 23 of the yellow gear 19Y (S5). The second motor 22 is stopped (S6). As a result, the positions of the ribs 23 of all the gears 19Y to 19BK can be made to coincide with the state shown in FIG. 7, and a color image without color misregistration is obtained by performing an image forming operation in the color mode in this state. be able to. Further, since the number of ribs 23 in each of the gears 19Y to 19BK in this example is five, the photosensitive drum may be rotated by a maximum of 1/5 turn before the motors 20 and 22 are stopped. The time required for phase matching can be shortened. Further, the positions of the ribs 23 of all the gears 19Y to 19BK can be matched by using only two sensors 25A and 25B.

  In the above-described example, the phase alignment operation for aligning the ribs 23 is performed immediately before the image forming operation in the color mode is started. However, when the image forming operation in the monochrome mode is completed, the rib positions of the respective gears are changed. You may make it stop each gear 19Y thru | or 19BK so that it may correspond.

  As described above, the control means of this example includes the color sensor 25B that detects the rib 23 of one color gear 19Y and the black sensor 25A that detects the rib 23 of the black gear 19BK. When the color sensor 19B detects the rib 23 of the rotating color gear 19Y, the color gear 19Y is stopped. When the black sensor 25A detects the rib 23 of the rotating black gear 19BK, the black color The gear 19BK is configured to stop.

  Each configuration described above is an intermediate transfer type image forming apparatus that transfers each toner image formed on a plurality of photosensitive drums onto a transfer material made of an intermediate transfer member, and transfers the superimposed toner image onto a recording medium. It can also be applied to.

It is a schematic sectional drawing which shows an example of an image forming apparatus. It is the schematic which shows an example of each photosensitive drum and the drive system which drives each photosensitive drum. FIG. 3 is a perspective view of a drive system that rotationally drives a black photosensitive drum. It is a perspective view which shows the gear for black and the gear for color. It is explanatory drawing which shows that the radius of the gear for black and the gear for color is non-uniform | heterogenous in the circumferential direction. It is a figure explaining the angular velocity fluctuation | variation of the black photosensitive drum and the color photosensitive drum. It is explanatory drawing which shows that the position of the rib of the gear for color and the gear for black is aligning. It is explanatory drawing which shows that the phase of the angular velocity fluctuation | variation of the color photosensitive drum and the black photosensitive drum is equal. It is a flowchart which shows the phase alignment operation | movement of the rib of a color gear and a black gear.

Explanation of symbols

3Y, 3M, 3C Color photosensitive drum 3BK Black photosensitive drum 19Y, 19M, 19C Color gear 19BK Black gear 21Y, 21M, 21C Color drive gear 21BK Black drive gear 23 Rib 25A Black sensor 25B Color sensor

Claims (3)

A plurality of color photosensitive drums on which chromatic toner images of different colors are respectively formed, one black photosensitive drum on which a black toner image is formed, and each color photosensitive drum are arranged concentrically, The color gears that rotate with the respective color photosensitive drums, the black gears that are arranged concentrically with the black photosensitive drums, and that rotate with the black photosensitive drums, A color driving gear meshing with the color gear; and a black driving gear meshing with the black gear for rotationally driving the black gear. The color photosensitive drum and the black photosensitive drum are rotated and driven. A color mode for forming a chromatic color toner image and a black toner image on a color photosensitive drum and a black photosensitive drum, respectively, and transferring each of the toner images on a transfer material to obtain a color image; It is possible to select a monochrome mode in which the optical drum is stopped, the black photosensitive drum is rotationally driven to form a black toner image on the black photosensitive drum, and the black toner image is transferred to a transfer material to obtain a black image. The plurality of color gears and black gears may be formed of molded products each having the same number of radially extending ribs.
When the black drive gear meshes with the smallest diameter portion of the black gear, the positions of the black drive gear and the color drive gear are set so that the color drive gear also meshes with the almost smallest diameter portion of the color gear. In addition, the distance between the transfer positions of the color photosensitive drum and the black photosensitive drum adjacent to each other is L, the number of ribs provided on each color gear and the black gear is k, the color photosensitive drum and the black photosensitive drum, respectively. When the diameter of the photosensitive drum is D and n is an integer,
L≈n (πD / k)
L, k, and D are set so as to satisfy the conditions, and in the color mode, the position of the rib in the circumferential direction of the color gear is substantially the same as the position of the rib in the circumferential direction of the black gear. An image forming apparatus comprising a gear and a black gear. The plurality of color gears are assembled so that the positions of the ribs in the circumferential direction substantially coincide with each other, and when the mode is switched from the monochrome mode to the color mode, prior to the execution of the color mode, the black gear The image forming apparatus according to claim 1, further comprising a control unit configured to substantially match a position of the rib in the circumferential direction with a position of the rib in the circumferential direction of the color gear. The control means includes a color sensor that detects a rib of one color gear and a black sensor that detects a rib of the black gear, and the color sensor includes a rib of the rotating color gear. 3. The image forming apparatus according to claim 2, wherein the color gear is stopped when detected, and the black gear is stopped when the black sensor detects a rib of the rotating black gear. apparatus.

Images