JP2016151675A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress a change in rotation of a photoreceptor drum due to a behavior of a recording medium.SOLUTION: On the downstream of a drum driving gear 29 transmitting a driving force to a photoreceptor drum 1, a sleeve driving gear 30 transmitting a driving force to a developing sleeve 5 is arranged. The developing sleeve 5 is in contact with the photoreceptor drum 1. The photoreceptor drum 1 is rotated quickly to put a backlash of the drum driving gear 29 constantly in one direction, and thereby suppressing a change in load on the photoreceptor drum 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus in which a latent image formed on a photosensitive drum is developed with toner, and a toner image is transferred and fixed on a recording medium for recording, and in particular, driving force is applied to the photosensitive drum. The present invention relates to a meshing structure of a transmission gear.

  In an image forming apparatus to which an electrophotographic process is applied, if a gear for driving a developing sleeve or a charging roller is engaged downstream of a drum coupling that rotates integrally with the photosensitive drum, the load of each gear or Unevenness in rotation occurs due to backlash or the like. In an image forming apparatus that forms an image at right angles to the scanning direction while scanning a laser beam on a photosensitive drum, so-called banding occurs in an image formed by uneven rotation of the photosensitive drum. In an image forming apparatus that forms a color image, color unevenness due to banding is caused.

  As a countermeasure against banding, conventionally, as shown in the block diagram of FIG. 6, a branching means for dividing the driving force is provided on the path for transmitting the driving force from the driving source to the drum driving gear. (For example, see Patent Document 1). That is, the developing sleeve and the charging roller are independently driven by the driving force divided by the branching unit, thereby eliminating the influence of the downstream gear load and backlash on the photosensitive drum.

JP-A-8-334934

  However, even if the rotation of the photosensitive drum is not affected by the downstream gear in this way, the load on the photosensitive drum is fluctuated due to disturbance such as the behavior of the recording medium, and the rotation of the photosensitive drum is caused. There was a problem that unevenness was likely to worsen. That is, a sudden change in the conveyance speed occurs when the recording medium conveyed while contacting the surface of the photosensitive drum during image formation enters or exits the roller nip, contacts the conveyance guide, or the like. This change spreads to the photoconductive drum, and the load on the photoconductive drum changes to cause uneven rotation, and the banding level of the formed image deteriorates.

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide an image forming apparatus capable of suppressing the rotational fluctuation of the photosensitive drum caused by the behavior of the recording medium. It is in.

In order to achieve the above object, the present invention provides:
A photosensitive drum on which a latent image is formed, and a developing device that uses the latent image as a toner image by toner supplied by a developing sleeve that contacts the photosensitive drum,
In an image forming apparatus having a drum driving gear for transmitting a driving force from a driving source to the photosensitive drum, and a sleeve driving gear for transmitting to a developing sleeve.
The sleeve drive gear is disposed downstream of the drum drive gear with respect to the drive source, and the driving force is transmitted through the drum drive gear.
The photosensitive drum and the developing sleeve are in contact with each other at least during image formation, and the developing sleeve receives a driving force from the sleeve driving gear so as to rotate in the opposite direction with respect to the photosensitive drum. The peripheral speed is set faster than that of the photosensitive drum.

  According to the present invention, it is possible to suppress the rotational fluctuation of the photosensitive drum caused by the behavior of the recording medium.

FIG. 3 is an explanatory cross-sectional view showing a transmission path of driving force from a driving source of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional explanatory view of the image forming apparatus of FIG. The block diagram which shows the transmission path | route of the driving force from the drive source of FIG. FIG. 2 is an explanatory diagram showing a meshing state between the drum driving gear of FIG. 1 and upstream and downstream idler gears. FIG. 2 is a cross-sectional explanatory view of the process cartridge of FIG. 1. FIG. 6 is a block diagram illustrating a driving force transmission path from a driving source of a conventional image forming apparatus. The figure which shows the relationship of the force which acts on a drum drive gear from an upstream idler gear and a downstream idler gear.

The present invention will be described below based on the illustrated embodiments.
First, the overall configuration of the image forming apparatus 28 to which the present invention is applied will be described with reference to FIG.
The illustrated image forming apparatus 28 is a so-called laser beam printer, and the latent image is converted into a toner image by the photosensitive drum 1 on which the latent image is formed and the toner supplied by the developing sleeve 5 in contact with the photosensitive drum 1. And a developing device 50.
A paper feed tray 9 on which a recording medium P such as recording paper is set is provided on the lower side of the apparatus. The recording medium P is disposed on the middle plate 21 in the paper feed tray 9, and the middle plate 21 is urged in the arrow z direction by the middle plate spring 22. Further, the intermediate plate 21 is provided with a paper feed cam contact portion 23, and the paper feed cam contact portion 23 is stationary at a position in contact with the paper feed cam 11.

When the drive is transmitted from the motor 33 which is a drive source and the paper feed roller 10 rotates, the paper feed cam 11 coaxial with the paper feed roller 10 also starts to rotate. As the sheet feeding cam 11 rotates, the radius of the surface in contact with the sheet feeding cam contact portion 23 changes, so that the intermediate plate 21 moves up and down with respect to the arrow z direction. When the intermediate plate 21 moves in the arrow z direction, the recording media P stacked on the paper feed tray 9 are fed one by one in order from the one stacked on the top surface.
The recording medium P sent out by the paper feed roller 10 enters the nip formed by the pressure contact between the transport driving roller 12 and the transport driven roller 13, and further by the transport driving roller 12 and the transport driven roller 13. It is conveyed downstream.

The photosensitive drum 1 and the developing device 50 are incorporated in the process cartridge 4, and the process cartridge 4 is detachably attached to the image forming apparatus main body 28A. The process cartridge 4 rotatably supports the photosensitive drum 1 and the developing sleeve 5, and the developing sleeve 5 contacts the photosensitive drum 1 at least during image formation and supplies toner to the photosensitive drum 1. ing. The process cartridge 4 is provided with a developer roller 6 (charger) that is rotatably supported and a developer container 6 that stores toner.
In the image formation, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2, and a latent image is drawn on the surface of the photosensitive drum 1 by the laser beam 3 emitted from the laser scanner unit 8, and this latent image is developed. Toner is supplied by the sleeve 5 to form a toner image. When the recording medium P is conveyed there, the toner image is transferred onto the recording medium P as an unfixed image at a transfer nip including the photosensitive drum 1 and the transfer roller 14.

  In order to heat and fix the transferred toner image, the recording medium P further passes through a nip composed of a fixing pressure roller 15 and a fixing heater 16, and the unfixed image is heat-fixed. The recording medium P after image fixing is directed along the conveyance guide 24 toward a paper discharge nip formed by the paper discharge driving roller 17 and the paper discharge driven roller 18. The paper discharge driving roller 17 and the paper discharge driven roller 18 discharge the recording medium P to the outside of the image forming apparatus 28, and the recording medium P is stacked above the paper discharge tray 19 and the paper discharge extension tray 25.

(Description of driving force transmission path)
Next, the configuration of the driving force transmission path of the image forming apparatus 28 according to the present embodiment will be described with reference to FIG.
The drive force transmission path is constituted by a gear train, and the drive force of the motor 33 as a drive source is transmitted to the downstream gear train by the motor pinion 27 that rotates together with the motor drive shaft. The driving force transmitted from the motor pinion 27 is transmitted to the drum driving gear 29 via a reduction gear 34 that is a reduction mechanism and a plurality of idler gears, in the illustrated example, four idler gears 35c, 35d, 35e, and 35a. Driving force is transmitted from the drum driving gear 29 further downstream to the sleeve driving gear 30 via the downstream idler gear 35b. The sleeve drive gear 30 is not a gear that is coaxial with the developing sleeve 5, but three idler gears are connected between the sleeve driving gear 30 and a gear (not shown) provided coaxially with the developing sleeve 5 to transmit the drive. It is. In short, as shown in FIG. 5, the gear train is determined so that the rotation direction of the developing sleeve 5 and the rotation direction of the photosensitive drum 1 are opposite.
The upstream idler gear 35a and the downstream idler gear 35b that mesh with the drum drive gear 29 in the upstream and downstream positions are at positions where the resultant force is reduced.
That is, the gear is arranged at a position where the resultant force (vector) of the following two forces applied to the drum drive gear 29 is small.
1) Driving force Fa received from the upstream idler gear 35a upstream of the drum driving gear 29
2) Reaction force Fb received from the downstream idler gear 35b on the downstream side of the drum drive gear 29
For example, FIG. 7A shows the gear configuration of FIG. 1, and FIG. 7B shows the gear configuration in which the arrangement of the downstream idler gear 35b is changed.
In FIG. 7A, the upstream idler gear 35a and the sleeve drive gear 30 are located on the opposite sides with respect to the straight line connecting the centers of the drum drive gear 29 and the sleeve drive gear 30. In FIG. 7B, the upstream idler gear 35 a and the sleeve drive gear 30 are arranged on the same side with respect to the straight line connecting the centers of the drum drive gear 29 and the sleeve drive gear 30.
In the arrangement relationship of FIG. 7B, the upstream idler gear 35a, the drum drive gear 29, and the downstream idler gear 35b are arranged close to a straight line, and the driving force Fa and reaction force Fb acting on the drum driving gear 29 are: It becomes almost parallel and the resultant force F is large.
On the other hand, in FIG. 7A, the angle between the driving force Fa and the reaction force Fb acting on the drum driving gear 29 is 90 ° or more, and the resultant force F is small.
The rotating shafts 29a and 30a of the drum driving gear 29 and the sleeve driving gear 30 are supported at both ends with respect to the image forming apparatus main body 28A, and the supporting strength is increased. Although not particularly illustrated, it is preferable that the image forming apparatus is supported by a sheet metal.

Further, the image forming apparatus 28 has a branching unit that divides the driving force through an idler gear 35 in a driving force transmission path from the motor pinion 27 to the drum driving gear 29. The driving force is transmitted to other systems. Although not particularly illustrated, the branching unit may employ various configurations such as a configuration in which an unillustrated gear is engaged with the idler gear 35 and a configuration in which another gear is fixed to the rotation shaft and the transmission path is branched.

  In this embodiment, the reduction gear 34 and the plurality of idler gears 35 are used as means for transmitting the driving force. However, the motor pinion 27 and the drum driving gear 29, and the drum driving gear 29 and the sleeve driving gear are not used. The driving force may be transmitted by directly engaging 30. The driving force transmission means from the driving source other than the upstream idler gear 35a and the downstream idler gear 35b that mesh with the drum driving gear 29 is not limited to a gear, and for example, the driving force is transmitted by a belt. Also good.

FIG. 3 is a block diagram showing how the driving force is transmitted in this embodiment.
The drum driving gear 29 supported in the image forming apparatus main body 28 </ b> A transmits driving force to the photosensitive drum 1 supported in the process cartridge 4 via the drum coupling 61. Similarly, the sleeve drive gear 30 supported in the image forming apparatus 28 transmits power to the developing sleeve 5 supported in the process cartridge 4 via the sleeve coupling 62. Further, power is transmitted from the sleeve coupling 62 to other systems such as the charging roller 2.
In the drawing, each component of the image forming apparatus main body 28A to which the driving force is transmitted is expressed as an abstract functional expression as a speed reduction unit, a paper feeding unit, a paper conveying unit, a fixing unit, and a paper discharging unit. 2, the drive source is the motor 33, the speed reduction means is the speed reduction gear 34, the paper feed means is the paper feed roller 10, the paper transport means is the transport drive roller 12, and the fixing means is fixing. The pressure roller 15 and the paper discharge means are a paper discharge drive roller 17. In FIG. 3, reference numerals of corresponding members are given to the blocks in which each function is expressed.

(Technical explanation for suppressing uneven rotation of the drum)
The upper part of FIG. 4 shows a meshing portion between the drum drive gear 29 and the upstream idler gear 35 a that is adjacent to the drum drive gear 29 and rotates in the direction of the arrow K ′ to transmit the drive force to the drum drive gear 29. It is. When the photosensitive drum 1 is ideally rotated without causing rotational fluctuation, the drum driving gear 29 receives a driving force that rotates in the direction of arrow K from the upstream idler gear 35a, and always backlashes in the same direction. Are tidy up.
However, in the prior art as shown in FIG. 6, when a sudden load is applied to the photosensitive drum 1, the direction of backlash between the drum driving gear 29 and the upstream idler gear 35a is not determined, and the photosensitive member is not fixed. Uneven rotation occurs in the drum 1. The sudden load is, for example, a change in the conveyance speed that occurs when the recording medium P enters the nip between the fixing pressure roller 15 and the fixing heater 16 or contacts the conveyance guide 24 during image formation.

In the present embodiment, in addition to the meshing of the upper gear in FIG. 4 described above, the drum drive gear 29 and the downstream idler gear 35b are meshed as shown in the lower part of FIG. The downstream idler gear 35b receives a driving force that rotates from the drum driving gear 29 in the direction of the arrow K ′. Further, as shown in FIG. 6 which is a cross-sectional view of the process cartridge 4, the developing sleeve 5 rotates in the opposite direction with respect to the photosensitive drum 1, in the direction of the arrow K ′ while contacting the photosensitive drum 1. The peripheral speed of the developing sleeve 5 is set so as to rotate fast with respect to the peripheral speed of the photosensitive drum 1, and the photosensitive drum 1 is rotated in the direction of arrow K.
By adopting the above configuration, even if a sudden load fluctuation occurs on the photosensitive drum 1, backlash is always offset as shown in the lower part of FIG. 4 to suppress uneven rotation of the photosensitive drum 1. It becomes possible.
As described above, according to the present invention, the sleeve driving gear 30 for transmitting the driving force to the developing sleeve 5 is disposed on the downstream side of the drum driving gear 29 for transmitting the driving force to the photosensitive drum 1. The developing sleeve 5 in contact with the photosensitive drum 1 is rotated faster than the photosensitive drum 1. By rotating in this way, the backlash of the drum drive gear 29 can always be offset in one direction, and fluctuations in the load on the photosensitive drum 1 can be suppressed.
In particular, the present invention is effective in a configuration in which sliding friction and rotational load are small with respect to the photosensitive drum 1. For example, as in the process cartridge of the present embodiment, a so-called cleaner-less configuration that does not have cleaning means for removing the developer on the surface of the photosensitive drum 1 while contacting the surface of the photosensitive drum 1 is provided. It is valid. However, the present invention is not limited to cleanerless, and the effect is also exhibited in the process cartridge 4 having cleaning means.

<Other embodiments>
In the above-described embodiment, the rotary monochrome image forming apparatus having one photosensitive drum 1 has been described. However, the present invention is not limited to this, and can also be applied to a tandem color image forming apparatus having a plurality of photosensitive drums 1. The present invention can also be applied to an image forming apparatus 28 that uses a transfer material carrying belt that carries and conveys a transfer material.
Furthermore, in the above-described embodiment, the image forming apparatus including the process cartridge that is detachable from the image forming apparatus main body has been described. However, the present invention can also be applied to an image forming apparatus that does not have a process cartridge.

In the above embodiment, the laser beam printer is described as an example of the image forming apparatus. However, the photosensitive drum is used as the image carrier, and an electrophotographic image forming process is applied thereto to form an electrostatic latent image. The present invention can be applied to various apparatuses that form an image on a recording medium. For example, electrophotographic printers other than laser beam printers (for example, LED printers), electrophotographic copying machines, electrophotographic facsimile machines, and electrophotographic word processors are included. Furthermore, a mono-color or full-color image forming apparatus that is used as an output device such as a multifunction peripheral or a workstation having these functions is included. The recording medium is an image on which an electrophotographic image forming apparatus forms an image, and includes, for example, paper, an OHP sheet, and the like.

P: Recording medium 1 Photosensitive drum 4 Process cartridge 5 Developing sleeve 27 Motor pinion 28 Image forming apparatus 28A Image forming apparatus main body 29 Drum drive gear 30 Sleeve drive gear 33 Motor (drive source)
35a Upstream idler gear 35b Downstream idler gear

Claims (5)

A photosensitive drum on which a latent image is formed, and a developing device that develops the latent image as a toner image with toner supplied by a developing sleeve that contacts the photosensitive drum,
In an image forming apparatus having a drum driving gear for transmitting a driving force from a driving source to the photosensitive drum, and a sleeve driving gear for transmitting to a developing sleeve.
The sleeve drive gear is disposed downstream of the drum drive gear with respect to the drive source, and the driving force is transmitted through the drum drive gear.
The photosensitive drum and the developing sleeve are in contact with each other at least during image formation, and the developing sleeve receives a driving force from the sleeve driving gear so as to rotate in the opposite direction with respect to the photosensitive drum. An image forming apparatus having a peripheral speed set higher than that of the photosensitive drum.   The photosensitive drum and the developing sleeve of the developing device are rotatably supported by a process cartridge that is detachably attached to the image forming apparatus main body, and the drum driving gear and the sleeve driving gear are provided in the image forming apparatus main body. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the drum driving gear and the sleeve driving gear are supported at both ends of a rotation shaft with respect to the image forming apparatus main body. 2. The image forming apparatus according to claim 1, wherein the gear that meshes with the drum drive gear upstream and downstream is disposed at a position where a resultant force of the force applied to the drum drive gear is reduced. 2. The image forming apparatus according to claim 1, wherein the photosensitive drum does not have a cleaning unit that removes the developer on the surface of the photosensitive drum while being in contact with the surface of the photosensitive drum.

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