JP2007094426A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the unevenness of image caused during image formation by reducing the number of gears used to transmit drive force from respective drive sources to a plurality of photoreceptors and a medium support means, thereby reducing the cumulation of backlash caused by the engagement of the gears. <P>SOLUTION: The gears are mounted on the rotary shafts of the plurality of photoreceptor drums 56 and close to the end faces of the drums so as to alternate on the right and left sides. In addition, a gear is mounted on the rotary shaft of a conveying-belt drive roller 65 and close to the end face of the roller. The gear on the photoreceptor drum 56 located closest to the conveying-belt drive roller 65 and the gear on the conveying-belt driver roller 65 are mounted on the opposite end faces of the drum. Disposing the gears in such positions makes it possible to make the radius of each gear larger than the outside diameter of the rotary shaft of the drum or roller adjacent to the center of the gear, leading to a smaller gear pitch. This reduces nonuniform image resulting from backlash of the gears. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a mechanism for suppressing uneven printing during color printing.

  Conventionally, as a color image forming apparatus, a developer is applied to an electrostatic latent image formed on the surface of a photosensitive drum using a developer of a plurality of colors, and a developer image of a plurality of colors is formed. Each color is applied to a color image forming apparatus that directly transfers a developer image onto a recording sheet conveyed by a conveying belt to form a color image, and an intermediate transfer belt that temporarily holds a developer image formed on a photosensitive drum. A color image forming apparatus is known in which a color image is formed by sequentially transferring the developer images to form a color image, and the color image is transferred to a recording sheet conveyed by a conveyance roller. Yes.

  In such a color image forming apparatus, it is necessary to drive the photosensitive drums and the intermediate transfer belts of the respective colors in synchronization with each other in order to prevent image unevenness at the time of image formation of each color and to obtain a good color image. is there. As a mechanism for synchronous driving of each drum and belt, each driving force of a driving source such as a motor is driven via a gear provided on a driving shaft of a photosensitive drum, an intermediate transfer belt, or a recording paper conveying belt. A driving force transmission mechanism that transmits to a shaft is known.

  However, in such a driving force transmission mechanism using gears, backlash occurs in the rotation of each drive shaft due to the meshing error of the teeth of each gear, and image unevenness called banding occurs in the color image.

As a mechanism for preventing this banding, a gear is provided on the end face on the same side of the drive shaft of each photosensitive drum, intermediate transfer belt, or recording paper transport belt, and the attachment position of the gear to the drive shaft is set in the axial direction. By shifting them from each other, adjacent gears are prevented from interfering with each other. A mechanism is known in which the gear radius is increased to the length up to the outer diameter of the drive shaft of the adjacent photoconductor, thereby increasing the number of gear teeth and reducing the pitch per gear rotation angle. . (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 10-312097

  By the way, in the driving force transmission mechanism using the gear as described above, the gear provided on each driving shaft can increase the gear radius only to the outer diameter of the adjacent driving shaft, so the number of gear teeth is increased. There are limitations. Therefore, the backlash cannot be suppressed below a certain value.

  As a method for avoiding this limitation, it is conceivable to make the gear teeth (module) as small as possible. However, if the gear teeth are made smaller, the dimensional tolerance of the gear meshing becomes strict, and the image forming apparatus has It leads to cost increase. In addition, since the strength of the gear teeth is also reduced, the life of the driving force transmission mechanism and thus the image forming apparatus is shortened.

  The present invention has been made in view of these problems, and an object of the present invention is to suppress image unevenness during color image formation in an image forming apparatus.

The invention according to claim 1, which has been made to achieve the above object, makes it possible to rotate the photosensitive member that forms an electrostatic latent image and develops the electrostatic latent image with a developer to obtain a developer image. A photosensitive member supporting shaft to be supported; and a medium supporting means for supporting a transfer medium onto which the developer image formed on the photosensitive member is transferred while being in contact with the surface of the photosensitive member so as to be movable relative to the photosensitive member surface. An image forming apparatus comprising: a driving source that generates a driving force for driving the photosensitive member and the medium supporting unit; and a driving force transmitting unit that transmits the driving force of the driving source to the photosensitive member and the medium supporting unit. The driving force transmitting means is mounted at least on the photosensitive member driving gear mounted on one end of the photosensitive member and the driving roller shaft for driving the medium supporting means, and the photosensitive member driving gear is mounted on the adjacent photosensitive member. A medium driving gear mounted on the end of the non-side The length from the rotation center of the photoconductor drive gear and the medium drive gear to the tooth tip of each gear is based on the length from the rotation center of the gear to the support shaft of the adjacent photoconductor or the drive roller shaft of the medium support means. Is also large.

  In the image forming apparatus configured as described above, the length from the center of the photosensitive member driving gear to the tooth tip and the length from the center of the medium driving gear to the tooth tip are the support shafts of the adjacent photosensitive members from the center of each gear. Or since it is larger than the length to the outer diameter of the drive roller shaft of a medium support means, the pitch per rotation angle of a gear can be made fine. Therefore, it is possible to suppress image unevenness that occurs during image formation due to backlash between the photosensitive member driving gear and the driving force transmission means.

  In addition, since the driving force transmission means and the driving source can be arranged with a good balance between the left and right, the weight balance as the image forming apparatus is improved and the image forming apparatus can be easily carried.

  The drive source for rotationally driving the photoconductor and the medium supporting unit is defined in claim 2. The photoconductor is supplied from the first drive source dedicated to the photoconductor via the first driving force transmission unit. So that the medium supporting means is rotationally driven by the driving force transmitted from the second driving source dedicated to the medium supporting means via the second driving force transmitting means. It may be configured to be driven by a dedicated drive source.

  By configuring the drive source in this way, the number of gears for transmitting the drive force from each drive source to the photosensitive member and the medium support means can be reduced, and the accumulation of backlash due to the meshing of the gears can be reduced. Image unevenness that occurs during image formation can be suppressed.

  In addition, since the drive source serving as the heat source can be disposed with a good balance between left and right, it is possible to reduce image quality degradation due to distortion of various components due to uneven distribution of heat inside the image forming apparatus.

  On the other hand, the drive source is configured as one drive source common to the photosensitive member and the medium supporting means as described in claim 3, and the drive force of the one drive source is the first and second drive forces. The signal may be transmitted through a transmission unit, and the photosensitive member and the medium support unit may be rotationally driven.

  With this configuration, the number of drive sources can be reduced, and the cost of the image forming apparatus can be reduced.

  When the transfer medium is configured to be conveyed by the medium support means as described in claim 4, a plurality of photoconductors are arranged in tandem for each color, and an image is directly formed on each recording medium from each photoconductor. In other words, it is possible to suppress image unevenness that occurs during image formation of a tandem color image forming apparatus using the so-called direct transfer method.

In addition to the configuration in which the recording medium is conveyed by the medium conveying unit, as described in claim 5, the developer image formed on the photosensitive member is transferred, and then the developer image is recorded on the recording medium. Alternatively, an intermediate transfer medium that temporarily holds the developer image until the image is transferred may be used as a transfer medium, and the transfer medium may be integrally formed on the surface of the recording medium support unit.

  With this configuration, a developer image is sequentially transferred from a plurality of photoconductors to an intermediate transfer medium to form a color image, and the color image is transferred to a recording medium. It is possible to suppress image unevenness that occurs during image formation of the image forming apparatus of the type.

Embodiments of the present invention will be described below with reference to the drawings. Example 1
FIG. 1 is a sectional view showing a schematic configuration of a color laser printer 1 to which the present invention is applied.

  In FIG. 1, a color laser printer 1 is a so-called horizontal type tandem color laser printer in which four image forming units 16 to be described later are arranged side by side in a horizontal direction. A paper feeding unit 4 for feeding recording paper 3 as a medium, an image forming unit 5 for forming an image on the fed recording paper 3, and a paper for discharging the recording paper 3 on which an image is formed A paper discharge unit 6 is provided.

  The paper feed unit 4 is provided at the bottom of the main body casing 2 so as to be detachably attached to the main body casing 2 from the front side, and above one end (upper front side) of the paper feed tray 12. A sheet feed roller 13 and a position above the sheet feed roller 13 and downstream of the sheet feed roller 13 in the conveyance direction of the recording paper 3 (hereinafter, the conveyance direction downstream side of the recording sheet 3 is the conveyance direction downstream side; 3 in the conveyance direction may be omitted as upstream in the conveyance direction.).

  The recording paper 3 is stacked in the paper feed tray 12, and the uppermost recording paper 3 is fed toward the transport roller 14 one by one by the rotation of the paper feeding roller 13. The toner is sequentially fed from the conveyance roller 14 to the space between the conveyance belt 67 and each photosensitive drum 56 (transfer position).

  A guide member 15 disposed in the vertical direction is provided between the paper feed roller 13 and the transport roller 14, and the recording paper 3 fed by the paper feed roller 13 is fed by the guide member 15. The sheet is sequentially fed between the conveyance belt 67 and the photosensitive drum 56 (transfer position).

  The image forming unit 5 transfers the images formed by the four image forming units 16Y, 16M, 16C, and 16K that form images and the image forming units 16 to the recording paper 3 in the intermediate portion in the main body casing 2. The image forming apparatus includes a transfer unit 17 and a fixing unit 18 that heats and presses an image transferred onto the recording paper 3 and fixes the image on the recording paper 3.

  Each image forming unit 16 has a photosensitive drum 56 as an image carrier, a charger 21 for charging the photosensitive drum 56 around the photosensitive drum 56, and an electrostatic latent image on the photosensitive drum 56. The scanner unit 19 is an electrostatic latent image forming unit to be formed, and the developing unit 20 is a developing unit that forms a developer image by attaching a developer to the photosensitive drum 56.

  The charger 21 is a scorotron type charger for positive charging that generates corona discharge from a charging wire made of tungsten or the like and uniformly charges the surface of the photosensitive drum 56 to positive polarity.

The scanner unit 19 includes a laser generator (not shown) that generates laser light for forming an electrostatic latent image on the surface of the photosensitive drum 56, a polygon mirror 23, and a pair in a scanner casing 22 as a casing. Lens 24 and 25, and three reflecting mirrors 26, 27 and 28.

  In this scanner unit 19, laser light (shown by a chain line in FIG. 1) emitted from the laser light emitting part is reflected by the polygon mirror 23, and the lens 24, the reflecting mirror 26, the reflecting mirror 27, the lens 25, and the reflecting mirror are reflected. 28 is sequentially passed through or reflected from the exit window 29. The laser beam emitted from the emission window 29 is scanned and irradiated on the photosensitive drum 56 to form an electrostatic latent image on the surface of the photosensitive drum 56.

  The developing unit 20 includes a developer hopper 31 as a developer container, a supply roller 32 as a developer supply unit, and a development roller 33 as a developer carrier in a development casing 43.

  The developer hopper 31 is formed as an internal space of the developing casing 43. The developer hopper 31 accommodates yellow (Y), magenta (M), cyan (C), and black (K) developers for each image forming unit 16.

  That is, in the four image forming units 16 described above, the image forming unit 16Y in which the developer hopper 31 stores yellow (Y) developer and the developer hopper 31 stores magenta (M) developer. Image forming unit 16M, image forming unit 16C in which cyan (C) developer is accommodated in developer hopper 31, and image forming unit 16K in which developer (hopper) 31 contains black (K) developer. It is configured.

  The supply roller 32 is disposed below the developer hopper 31, and a metal roller shaft is covered with a roller portion made of a conductive sponge member. The supply roller 32 is rotatably supported so as to rotate in the opposite direction to the developing roller 33 at a nip portion facing and contacting the developing roller 33.

  The developing roller 33 is rotatably disposed below the supply roller 32 at a position facing and in contact with the supply roller 32. The developing roller 33 is formed by covering a metal roller shaft with a roller portion made of an elastic member such as a conductive rubber material.

  The transfer unit 17 is provided on the opposite side of the developing unit 20 in the main body casing 2 so as to face the photosensitive drum 56. The transfer unit 17 includes a transport belt driving roller 65, a transport belt driven roller 66, a transport belt 67 that is an endless belt, and a transfer roller 68.

  The conveyance belt driven roller 66 is disposed in front of the photosensitive drum 56 of the image forming unit 16 </ b> Y on the most upstream side with respect to the conveyance direction of the recording paper 3 and on the upper rear side of the paper supply roller 13. Further, the conveying belt driving roller 65 is disposed behind the photosensitive drum 56 of the black image forming unit 16K on the most downstream side with respect to the conveying direction of the recording paper 3 and obliquely below and below the fixing unit 18. Has been.

  The conveyor belt 67 is wound between the conveyor belt driving roller 65 and the conveyor belt driven roller 66. The conveyor belt 67 is disposed such that the outer surface around which it is wound is in contact with all the photosensitive drums 56 of each image forming unit 16.

The conveyance belt driven roller 66 is driven by the driving of the conveyance belt driving roller 65, and the conveyance belt 67 is interposed between the conveyance belt driving roller 65 and the conveyance belt driven roller 66 and the photosensitive drum 56 of each image forming unit 16. In a counterclockwise direction so as to rotate in the same direction as that of the photosensitive drum 56 on the contact surface facing and facing.

  Further, the transfer roller 68 is disposed inside the wound conveyance belt 67 so as to face the photosensitive drum 56 of each image forming unit 16 with the conveyance belt 67 interposed therebetween. The transfer roller 68 is formed by covering a metal roller shaft with a roller portion made of an elastic member such as a conductive rubber material.

  The transfer roller 68 is rotatably provided in the counterclockwise direction so that the transfer roller 68 rotates in the same direction as the circumferential movement direction of the conveyor belt 67 on the contact surface facing the conveyor belt 67. A predetermined voltage is applied from a power source (not shown) in a direction in which the developer image carried on the photosensitive drum 56 is transferred (transferred) to the recording paper 3, and the transfer roller 68, the photosensitive drum 56, and the like are controlled by constant current control. An appropriate transfer bias is applied during this period.

  The fixing unit 18 is disposed behind the image forming unit 16 and the transfer unit 17 and on the downstream side in the transport direction. The fixing unit 18 includes a heating roller 70 and a pressure roller 69. The heating roller 70 is made of a metal base tube having a release layer formed on the surface thereof, and a halogen lamp is provided along the axial direction thereof. Then, the surface of the heating roller 70 is heated to the fixing temperature by the halogen lamp. The pressure roller 69 is disposed so as to press the heating roller 70.

  The paper discharge unit 6 is disposed in the upper part of the main body casing 2 on the downstream side in the transport direction of the fixing unit. The paper discharge unit 6 is provided with a pair of paper discharge rollers 11 for discharging the recording paper 3 on which image fixing has been completed to a paper discharge tray, and a downstream side of the paper discharge rollers 11, and all image forming processes are performed. A paper discharge tray 10 for accumulating the finished recording paper 3 is provided.

  In the color laser printer 1 according to the present embodiment as described above, the surface of the photosensitive drum 56 is uniformly charged by the charger 21, and the laser beam modulated according to the image information from the scanner unit 19 (illustrated by a chain line in FIG. 1). ) Is formed, an electrostatic latent image is formed on the surface of the photosensitive drum 56. The electrostatic latent image is visualized with a developer on the photosensitive drum 56 by the developing unit 20 and conveyed to the transfer position by the rotation of the photosensitive drum 56.

  At the transfer position, the recording paper 3 is supplied via the paper feed roller 13 and the conveyance roller 14, and the visible image (developer image) is transferred to the recording paper 3 by the transfer bias voltage applied by the transfer roller 68. The

  Next, the recording paper 3 is conveyed to the fixing unit 18 and is nipped and conveyed by the heating roller 70 and the pressure roller 69 of the fixing unit 18, and the visible image (developer image) on the recording paper 3 is heated and pressurized. And fixed on the recording paper 3. Then, the recording paper 3 is discharged by the paper discharge roller 11 to the paper discharge tray 10 above the color laser printer 1, and the image forming operation is completed.

  Next, the drive mechanism of the photosensitive drum 56 and the conveyance belt drive roller 65 in the color laser printer 1 of the first embodiment will be described in detail with reference to FIG.

  FIG. 2 illustrates only a portion related to the driving mechanism of the photosensitive drum 56 and the conveying belt driving roller 65, omitting other components, in order to explain the driving mechanism of the photosensitive drum 56 and the conveying belt driving roller 65. It is the top view which looked at from the top. In FIG. 2, a side view of the drive mechanism and a top view seen from another angle are also shown for easy understanding of the arrangement of the drive mechanism.

As shown in FIG. 2, the rotating shafts (photosensitive member support shafts) of the photoconductive drums 56Y, 56M, 56C, and 56K are adjacent to the end surfaces of the respective drums, and are arranged to the left and right in the direction of the arrangement of the rotating shafts Photosensitive drum gears 80Y, 80M, 80C, and 80K are alternately mounted on the end surfaces. A conveyance belt driving roller gear 81 is mounted on the rotation shaft of the conveyance belt driving roller 65 in the vicinity of the end surface of the roller.

  The photosensitive drum gear 80Y mounted on the photosensitive drum 56Y closest to the transport belt drive roller 65 and the transport belt drive roller gear 81 mounted on the transport belt drive roller 65 are mutually drum end surfaces. It is attached to the opposite end.

  The photosensitive drum gears 80Y, 80M, 80C, and 80K attached to the photosensitive drums are respectively photosensitive drum driving motor gears 85Y attached to the rotation shafts of the photosensitive drum driving motors 84Y, 84M, 84C, and 84K. , 85M, 85C, 85K. Then, the rotation of the output shaft of each photoconductor drum drive motor 84Y, 84M, 84C, 84K is transmitted to the rotation shaft of each photoconductor drum 56Y, 56M, 56C, 56K via these gears, and each photoconductor. The drums 56Y, 56M, 56C, and 56K are driven.

  Further, the conveyance belt drive roller gear 81 attached to the conveyance belt drive roller 65 is fitted to the conveyance belt drive motor gear 91 attached to the output shaft of the conveyance belt drive motor 90. The rotation of the output shaft is transmitted to the rotation shaft of the conveyor belt drive roller 65 through these gears, and the conveyor belt drive roller 65 is driven.

  Here, the photosensitive drum drive motors 84Y, 84M, 84C, and 84K and the conveyance belt drive motor 90 are controlled to operate synchronously by a controller (not shown).

  As described above, the photosensitive drum gears 80Y, 80M, 80C, and 80K mounted on the photosensitive drums 56Y, 56M, 56C, and 56K are arranged at the left and right end surfaces toward the rotating shafts of the photosensitive drums in the arrangement direction of the rotating shafts. Are alternately mounted, the photosensitive drum gears 80Y, 80M, 80C and 80K do not interfere with each other. Further, the photosensitive drum gears 80Y, 80M, 80C, and 80K do not interfere with the rotating shafts of the adjacent photosensitive drums 56Y, 56M, 56C, and 56K. Accordingly, the diameter from the rotation center of each photoconductor drum gear 80 to the tooth tip can be made larger than the length from the rotation center of the gear to the outer diameter of the rotation shaft of the adjacent photoconductor drum 56. The pitch per rotation angle of the drum gear 80 can be made fine. Further, since the pitch per rotation angle of the gear can be made fine, the unevenness of the image generated at the time of image formation is suppressed by the play of the meshing between the photosensitive drum gears 80 and the gears of the photosensitive drum driving motors 84. Is possible.

  Even if the diameter from the rotation center of each photoconductor drum gear 80 to the tooth tip can be made larger than the length from the rotation center of the gear to the outer diameter of the rotation shaft of the adjacent photoconductor drum 56, In the example shown in FIG. 2, a total of four photoconductor drums 56Y, 56M, 56C, and 56K are arranged at a predetermined pitch in order to correspond to the formation of four-color images. The length to the outer diameter of the rotating shaft of the drum 56 must be smaller. For example, the photosensitive drum gear 80Y must prevent the tooth tip from interfering with the rotation shaft of the photosensitive drum 56K, and the photosensitive drum gear 80K can prevent the tooth tip from interfering with the rotation shaft of the photosensitive drum 56M. I have to do it. There is no such limitation on the photosensitive drum gears 80C and 80M. However, from the viewpoint of keeping the rotational accuracy constant or suppressing the increase in the number of parts, the diameters of all the photosensitive drum gears 80Y, 80M, 80C, and 80K. It is desirable to make them equal and to be composed of the same parts.

Further, since the conveyance belt drive roller gear 81 and the photosensitive drum gear 80Y adjacent to the conveyance belt drive roller gear 81 are mounted on the opposite ends of the rollers and the drums to which the respective gears are mounted, the conveyance belt drive roller gear 81 and the photosensitive drum gear 80Y are connected. There is no interference. Further, the conveyance belt drive roller gear 81 does not interfere with the rotating shaft of the adjacent photosensitive drum 56Y. Therefore, the length from the rotation center of the photosensitive drum gear 80Y to the tooth tip can be made larger than the distance from the rotation center of the gear to the outer diameter of the rotation shaft of the adjacent photosensitive drum 56, and the rotation angle of the gear. The pitch around can be made fine. Further, since the pitch per rotation angle of the gear can be made fine, it is possible to suppress image unevenness that occurs at the time of image formation due to backlash between the photosensitive drum gear 80 and the gear of the photosensitive drum driving motor 84. It becomes.

  Further, since the gears and the motors can be arranged with a good left / right balance, the weight balance of the image forming apparatus is improved, and the image forming apparatus can be easily carried.

  In addition, since the motors serving as heat sources can be arranged in a balanced manner on the left and right, it is possible to reduce image quality degradation due to distortion of various components due to uneven distribution of heat inside the image forming apparatus.

  In the above embodiment, the photosensitive drum driving motor 84 is used for each photosensitive drum 56 in order to drive each photosensitive drum 56. However, as shown in FIG. 3, the photosensitive drum 56Y is used. And 56C may be driven using one photosensitive drum driving motor 84A, and the photosensitive drums 56M and 56K may be driven using one photosensitive drum driving motor 84B.

  That is, the photosensitive drum driving motor gear 85A mounted on the output shaft of the photosensitive drum driving motor 84A is fitted in the portion where the photosensitive drum gears 80Y and 80C overlap, and the photosensitive drum driving is performed via each gear. The rotation of the output shaft of the motor 84A is transmitted to the photosensitive drums 56Y and 56C, and the photosensitive drums 56Y and 56C are rotated.

  Similarly, the photosensitive drums 56M and 56K are rotated by the photosensitive drum driving motor 84B.

In this case, it is necessary to increase the output of the photosensitive drum driving motor 84 as compared with the case where each photosensitive drum 80 is driven using a dedicated photosensitive drum driving motor 84. The number of drive motors 84 can be reduced, and the cost of the image forming apparatus can be reduced.
(Example 2)
In the second embodiment, the configuration and operation of the color laser printer 1 are compared with the first embodiment, the description of the same parts as those in the first embodiment is omitted, and the differences will be described in detail.

  The color laser printer according to the first embodiment is a so-called direct tandem type color laser printer. The developer images formed on the photosensitive drums 56Y to 56K are sequentially printed directly on the recording paper 3, and the recording paper 3 This is a color laser printer that forms a color image on the surface.

  In contrast, the color laser printer 1 according to the second embodiment is a so-called four-cycle color laser printer.

In this type of color laser printer, as shown in FIG. 4, a developer image is formed by applying a developer to an electrostatic latent image formed on a photoreceptor belt 71, which will be described later, by a developing unit 20. The image forming process of forming the image by transferring the developed developer image onto an intermediate transfer belt 74 described later is performed for each of the yellow (Y), magenta (M), cyan (C), and black (K) colors. A color image is formed repeatedly on the surface of the intermediate transfer belt 74, and the intermediate transfer belt 74 on which the color image is formed is brought into contact with the recording paper 3 conveyed by the transfer roller 68 or the like, A color image is formed.

  Here, the photosensitive belt 71 is wound so as to draw a triangle between the photosensitive belt driving roller 72 and the two photosensitive belt driven rollers 73, and the wound outer surface is formed. The developing units 20 are disposed so as to face each other.

  The photosensitive belt driven roller 73 has a structure that is pulled by a spring or the like outside the triangle drawn by the photosensitive belt 71 so as to apply an appropriate tension to the photosensitive belt 71.

  The photosensitive belt driven roller 73 is driven by the driving of the photosensitive belt driving roller 72, and accordingly, the photosensitive belt 71 is moved between the photosensitive belt driving roller 72 and the photosensitive belt driven roller 73. It moves around so as to face and face.

  Next, the intermediate transfer belt 74 is wound so as to draw a triangle between the intermediate transfer belt driving roller 75 and the two intermediate transfer belt driven rollers 76, and the outer surface that is wound is The intermediate transfer belt drive roller 75 is disposed in contact with the photosensitive belt 71.

  The intermediate transfer belt driven roller 76 is pulled by a spring or the like outside the triangle drawn by the intermediate transfer belt 74 so as to apply an appropriate tension to the intermediate transfer belt 74.

  As the intermediate transfer belt driving roller 75 is driven, the intermediate transfer belt driven roller 76 is driven, and accordingly, the intermediate transfer belt 74 is in contact with the photosensitive belt 71 and the photosensitive belt driving roller 72. It moves around in the opposite direction to the photoreceptor belt 71.

  As shown in FIG. 5, a photosensitive belt driving roller gear 82 is attached to one end of the photosensitive belt driving roller 72, and is one end of the intermediate transfer belt driving roller 75, and the photosensitive body of the photosensitive belt driving roller 72. An intermediate transfer belt drive roller gear 83 is mounted on the end surface opposite to the end surface on which the belt drive roller gear 82 is mounted.

  A photoconductor belt drive motor 86 is disposed in the vicinity of the photoconductor belt drive roller gear 82, and a photoconductor belt drive motor gear 87 is mounted on the output shaft of the photoconductor belt drive roller gear 82. It is like that.

  Then, the rotation of the output shaft of the photosensitive belt driving motor 86 is transmitted to the photosensitive belt driving roller 72 via the photosensitive belt driving motor gear 87 and the photosensitive belt driving roller gear 82 to rotate the photosensitive belt 71 around. .

  Further, an intermediate transfer belt drive motor 88 is disposed in the vicinity of the intermediate transfer belt drive roller gear 83, and an intermediate transfer belt drive motor gear 89 is attached to the output shaft of the intermediate transfer belt drive roller gear 83 so as to be engaged with the intermediate transfer belt drive roller gear 83. It is like that.

  The rotation of the output shaft of the intermediate transfer belt drive motor 88 is transmitted to the intermediate transfer belt drive roller 75 via the intermediate transfer belt drive motor gear 89 and the intermediate transfer belt drive roller gear 83, and the intermediate transfer belt 74 is moved around. .

The photosensitive belt driving motor 86 and the intermediate transfer belt driving motor 88 are controlled to operate synchronously by a controller (not shown).

  As described above, since the photosensitive belt driving roller gear 82 and the intermediate transfer belt driving roller gear 83 are mounted on opposite ends of the driving rollers, the photosensitive belt driving roller gear 82 and the intermediate transfer belt driving roller gear 83 interfere with each other. In addition, the gears and the rotation shafts of the drive rollers do not interfere with each other. Therefore, the radius of the photosensitive belt driving roller gear 82 can be made larger than the distance from the center of the gear to the center of the rotation shaft of the intermediate transfer belt driving roller, and the pitch per rotation angle of the gear can be made fine. Since the pitch per rotation angle of the gear can be made fine, the engagement between the photosensitive belt driving roller gear 82 and the photosensitive belt driving motor gear 87 and the intermediate transfer belt driving roller gear 83 and the intermediate transfer belt driving motor gear are reduced. It is possible to suppress image unevenness that occurs during image formation due to the looseness of engagement with 89.

  Further, since the gears and the motors can be arranged with a good left / right balance, the weight balance of the image forming apparatus is improved, and the image forming apparatus can be easily carried.

  In addition, since the motors serving as heat sources can be arranged in a balanced manner on the left and right, it is possible to reduce image quality degradation due to distortion of various components due to uneven distribution of heat inside the image forming apparatus.

  In the second embodiment, the photosensitive belt driving roller 72 and the intermediate transfer belt driving roller 75 are driven by separate motors (photosensitive belt driving motor 86 and intermediate transfer belt driving motor 88). As shown, it may be driven by a single drive motor 92.

  That is, the output shaft 96 of the drive motor 92 disposed in the vicinity of the photosensitive belt drive roller gear 82 is extended to the side where the intermediate transfer belt drive roller gear 83 is mounted, and the drive motor gear 93 is provided at the root and tip of the output shaft. , 94 is installed. The drive motor gear 93 is engaged with the photosensitive belt drive roller gear 82, and the drive motor gear 94 is engaged with the idle gear 95 disposed at a position where the drive motor gear 94 is engaged with the intermediate transfer belt drive roller gear 83. Then, the rotation of the output shaft of the drive motor 92 is transmitted to each drive roller via each gear, and the intermediate transfer belt 74 and the photosensitive belt 71 are rotated in a synchronized manner.

  In this case, only one drive motor is required to rotate each belt in a circular motion, and the cost of the image forming apparatus can be reduced.

  Further, since there is only one drive motor, a control device for synchronizing the circular movement of each belt is not required, and the cost of the image forming apparatus can be reduced.

  The configuration of the second embodiment shown in FIG. 6 can also be applied to the first embodiment as necessary. For example, if the rotation of the conveyance belt drive motor 90 shown in FIG. 2 is transmitted to the photosensitive drum gear 80K via the idle gear as in FIG. 6, the photosensitive drum motor 84K can be omitted. Become.

  Further, if the photosensitive drum gears 80Y, 80M, 80C are rotated in conjunction with the photosensitive drum gear 80K by interposing intermediate gears between the photosensitive drum gears 80K, 80Y, 80M, 80C, etc. Can be driven by one drive motor (conveyance belt drive motor) 90, and the photosensitive drum motors 84Y, 84M, and 84C can be omitted.

  In the first and second embodiments, the case where the present invention is applied to the color laser printer 1 has been described. However, instead of the scanner unit 19, an LED printer that performs exposure using LEDs (light emitting diodes). The present invention can be applied to an image forming apparatus such as an electronic color copying apparatus or a color facsimile apparatus provided with an original reading means for electronically reading an original, and the same as described above. The effect of can be obtained.

1 is a cross-sectional view illustrating a schematic configuration of a color laser printer 1 according to a first embodiment to which the present invention is applied. In the color laser printer 1 of the first embodiment, each photosensitive drum 56 is an explanatory diagram when operated by a dedicated drive source. In the color laser printer 1 of Example 1, each photosensitive drum 56 is divided into groups, and the photosensitive drum 56 is operated by a drive source for each group. It is sectional drawing which shows schematic structure of the color laser printer 1 of Example 2 to which this invention was applied. FIG. 6 is an explanatory diagram of a photosensitive belt driving roller 72 and an intermediate transfer belt driving roller 75 in the color laser printer 1 of Example 2. FIG. 6 is an explanatory diagram of a drive motor 92, an intermediate transfer belt drive roller 75, and a photosensitive belt drive roller 72 in the color laser printer 1 of Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Color laser printer, 2 ... Main body casing, 3 ... Recording paper, 4 ... Paper feed part, 5 ... Image forming part, 6 ... Paper discharge part, 9 ... Photosensitive unit, 10 ... Paper discharge tray, 11 ... Paper discharge Roller, 12 ... feed tray, 13 ... feed roller, 14 ... conveying roller, 15 ... guide member, 16, 16Y, 16M, 16C, 16K ... image forming unit, 17 ... transfer section, 18 ... fixing section, 19 ... Scanner unit, 20 ... developing unit, 21 ... charger, 23 ... polygon mirror, 24, 25 ... lens, 26, 27, 28 ... reflecting mirror, 29 ... ejecting window, 31 ... developer hopper, 32 ... feed roller, 33 ... developing roller, 43 ... developing casing, 56, 56Y, 56M, 56C, 56K ... photosensitive drum, 65 ... conveying belt driving roller, 66 ... conveying belt driven roller, 67 ... conveying belt, 68 ... Copy roller, 69 ... Pressure roller, 70 ... Heating roller, 71 ... Photoconductor belt, 72 ... Photoconductor belt drive roller, 73 ... Photoconductor belt driven roller, 74 ... Intermediate transfer belt, 75 ... Intermediate transfer belt drive roller, 76 ... Intermediate transfer belt driven roller, 80 ... Photoconductor drum gear, 81 ... Conveyor belt drive roller gear, 82 ... Photoconductor belt drive roller gear, 83 ... Intermediate transfer belt drive roller gear, 84 ... Photoconductor drum drive motor, 85 ... Photoconductor drum Drive motor gear, 86 ... Photoconductor belt drive motor, 87 ... Photoconductor belt drive motor gear, 88 ... Intermediate transfer belt drive motor, 89 ... Intermediate transfer belt drive motor gear, 90 ... Conveyor belt drive motor, 91 ... Conveyor belt drive motor gear, 92 ... Drive motor, 93, 94 ... Drive motor gear, 95 ... Idle gear, 96 The output shaft.

Claims (5)

A photosensitive member supporting shaft that rotatably supports a photosensitive member that forms an electrostatic latent image and develops the electrostatic latent image with a developer to obtain a developer image;
Medium support means for supporting a transfer medium onto which the developer image formed on the photoconductor is transferred while being in contact with the surface of the photoconductor and movable relative to the surface of the photoconductor;
A driving source for generating a driving force for driving the photosensitive member and the medium supporting unit;
An image forming apparatus comprising: a driving force transmitting unit configured to transmit a driving force of the driving source to the photosensitive member and the medium supporting unit;
The driving force transmission means is
At least a photosensitive member driving gear attached to one end of the photosensitive member;
A drive roller shaft for driving the medium support means, and a medium drive gear mounted on an end of the adjacent photosensitive body where the photoconductor drive gear is not mounted;
The length from the rotation center of the photoconductor drive gear and the medium drive gear to the tooth tip of each gear is the length from the rotation center of the gear to the support shaft of the adjacent photoconductor or the drive roller shaft of the medium support means. An image forming apparatus characterized in that it is larger than the above. The photosensitive member is rotationally driven by a driving force transmitted from a first driving source dedicated to the photosensitive member via a first driving force transmission unit,
The image forming apparatus according to claim 1, wherein the medium supporting unit is rotationally driven by a driving force transmitted from a second driving source dedicated to the medium supporting unit via a second driving force transmitting unit. apparatus.   The drive source is configured as one drive source common to the photosensitive member and the medium supporting unit, and rotationally drives the photosensitive member and the medium supporting unit via the first and second driving force transmitting units. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, wherein the transfer medium is a recording medium conveyed by the medium support unit.   The transfer medium is an intermediate transfer member that temporarily holds the developer image until the developer image formed on the photoconductor is transferred and thereafter the developer image is transferred to the recording medium. The image forming apparatus according to claim 1, wherein the image forming apparatus is integrally formed on a surface of the medium support unit.