JP2001272878A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image of high quality free from banding by suppressing the velocity fluctuation of a photoreceptor. SOLUTION: Rotary driving force by a driving motor is applied to a drum driving gear 8 fixed to an intermediate transfer drum 41 on the rotary shaft of the drum 41 to rotate the intermediate transfer drum 41. Besides, a photoreceptor driving gear 9 is fixed to the photoreceptor 21 on the rotary shaft of the photoreceptor 21 under the condition where the photoreceptor driving gear 9 is engaged with the drum driving gear 8. In the case that the number of teeth of the gear 8 and the number of teeth of the gear 9 are expressed by Z1 and Z2, respectively, and the diameter of the intermediate transfer drum 41 and the diameter of the photoreceptor 21 are expressed by D1 and D2, respectively, the following inequality is satisfied; Z2/Z1>D2/D1. Consequently, even in the case that external force working in a direction of accelerating the circumferential velocity of the photoreceptor 21 is applied on the photoreceptor 21, the drum driving gear 8 functions as a stopper for the photoreceptor driving gear 9, then, the circumferential velocity fluctuation of the photoreceptor 21 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for transferring a toner image formed on a photosensitive member to a transfer medium such as a transfer belt, a transfer drum, and a recording material wound around the transfer drum.

[0002]

2. Description of the Related Art In an image forming apparatus such as a printer, a facsimile, a copying machine, etc., a process of primary transfer of a toner image formed on a photoreceptor to an intermediate transfer member is performed by yellow (Y), cyan (C), magenta ( M), black (K)
These four color toner images are superimposed on a transfer medium to form a color toner image. Then, the color toner image is secondarily transferred to the recording material by a secondary transfer roller to form a color image on the recording material, and further, the toner image on the recording material surface is heated by a fixing unit to form a color image on the recording material. Has been established. Here, as a transfer medium, a drum-shaped transfer drum or a transfer belt using an endless belt has been conventionally used.

Instead of forming an intermediate color image on a transfer drum or a transfer belt as described above, a recording material is wound around the surface of the transfer drum, and a toner image on a photoreceptor is transferred onto the recording material. An image forming apparatus is conventionally known.

In order to execute the above-described primary transfer processing,
In a conventional image forming apparatus, four colors (yellow (Y), cyan (C), magenta (M), and black (K)) are developed around a photoreceptor along a rotation direction thereof as charging means and developing means. A container and a cleaning unit are arranged respectively. Then, after the outer peripheral surface of the photoconductor 21 is uniformly charged by the charging unit, a laser beam is irradiated from the exposure unit toward the outer peripheral surface of the photoconductor 21 to form an electrostatic latent image. Subsequently, one of the four developing devices is selectively brought into contact with the photoconductor, and a developing bias is applied to the developing device. As a result, the toner of the selected color is applied to the surface of the photoconductor, and the electrostatic latent image on the photoconductor is made visible. The toner image developed by the developing unit is primarily transferred onto a transfer belt, a transfer drum, or a recording material held on the surface of the transfer drum.

[0005]

By the way, in the above-mentioned image forming apparatus, the developing device is previously arranged at a distance from the photoconductor, and one of the developing devices selected only when the developing process is performed is applied to the photoconductor. Touch The speed of the photosensitive member fluctuates due to the impact of the contact with the developing device, and an image defect called banding may occur. Further, even while the developing device is in contact with the photoreceptor, the driving force of the photoreceptor becomes unstable due to the interaction force applied to the photoreceptor by the developing device, which may cause an image defect.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide an image forming apparatus capable of forming a high-quality image without banding by suppressing speed fluctuation of a photosensitive member.

[0007]

One aspect of the present invention relates to an image forming apparatus for transferring a toner image formed on a drum-shaped photosensitive member to a surface of a transfer drum or a recording material wound around the surface. A drum drive gear fixed to the transfer drum on a rotation axis of the transfer drum, and a drum drive gear fixed to the photoreceptor on a rotation axis of the photoreceptor. And a drive unit that rotationally drives the drum drive gear. The number of teeth of the drum drive gear is Z1, the number of teeth of the photoconductor drive gear is Z2, Assuming that the diameter is D1 and the diameter of the photoreceptor is D2, the following inequality is satisfied: Z2 / Z1> D2 / D1.

In an image forming apparatus satisfying the above inequality,
The rotational driving force from the driving unit is applied to the drum driving gear to rotate the transfer drum, and its peripheral speed is faster than the peripheral speed of the photoconductor. On the other hand, on the photoreceptor side, a photoreceptor drive gear is fixed to the photoreceptor on the rotation axis of the photoreceptor, and meshes with the drum drive gear. Therefore, the photoconductor rotates following the transfer drum in a state where the rotation-side tooth surface of the photoconductor drive gear is locked to the anti-rotation direction tooth surface of the drum drive gear. As a result, even if an external force acting in the direction of increasing the peripheral speed of the photoconductor acts on the photoconductor, the drum drive gear functions as a stopper and stabilizes the peripheral speed of the photoconductor.

Another aspect of the present invention relates to an image forming apparatus for transferring a toner image formed on a drum-shaped photoreceptor to an intermediate transfer belt. A belt driving gear fixed to the driving roller on a rotation axis of the driving roller, and a belt driving gear fixed to the photosensitive member on a rotation axis of the photoconductor. And a drive unit that rotationally drives the belt drive gear. The number of teeth of the belt drive gear is Z1, the number of teeth of the photoconductor drive gear is Z2, and the number of teeth of the drive roller is Assuming that the diameter is D1 and the diameter of the photoreceptor is D2, the following inequality is satisfied: Z2 / Z1> D2 / D1.

In the image forming apparatus having the above-mentioned structure, the photosensitive member is also subjected to the intermediate transfer in a state in which the rotation-side tooth surface of the photosensitive member driving gear is engaged with the anti-rotation side tooth surface of the belt driving gear. It rotates following the belt. As a result, even if an external force acting in the direction of increasing the peripheral speed of the photoconductor acts on the photoconductor, the belt drive gear functions as a stopper and stabilizes the peripheral speed of the photoconductor.

[0011]

FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. This image forming apparatus includes yellow (Y), magenta (M), cyan (C),
The apparatus forms a full-color image by superimposing four black (K) toners, or forms a monochrome image using only black (K) toner. In this image forming apparatus, when an image forming command (a signal indicating the content of a print request) is given to the control unit from an external device such as a host computer, the main controller provided in the control unit operates the engine unit 1 of the image forming apparatus. The job data (print information) is converted into the job data (print information) suitable for the operation instruction, and is provided to the sub controller. The sub-controller receiving this controls the engine unit 1 of the image forming apparatus according to the job data.

In the engine unit 1, a toner image can be formed on the photosensitive member 21 of the image forming unit 2. That is, the image forming unit 2 includes a photoconductor 21 rotatable in the direction of the arrow in FIG. 1, and further includes a charging roller 22 as a charging unit around the photoconductor 21 along the rotation direction.
Developing devices 23Y, 23M, 23C, 23 as developing means
K and the cleaning unit 24 are arranged respectively. The configuration for driving the photoconductor 21 will be described later.

A charging bias is applied to the charging roller 22 from a charging bias circuit (not shown).
To uniformly charge the outer peripheral surface. The photosensitive member 21 charged by the charging roller 22
Exposure unit 3 irradiates laser beam LB toward the outer peripheral surface of. The exposure unit 3 scans and exposes the laser beam LB onto the photoconductor 21 in accordance with image data obtained by developing the image forming command into an image, and forms an electrostatic latent image corresponding to the image forming command on the photoconductor 21. Form.

The electrostatic latent image thus formed is developed
Is developed with toner. That is, in this embodiment, the developing unit 23 includes a developing unit 23Y for yellow, a developing unit 23M for magenta, a developing unit 23C for cyan, and a developing unit 23K for black.
It is provided rotatable around 1). These developing units 23Y, 23M, 23C, and 23K are rotated and positioned in this order, and selectively contact the photoconductor 21 to apply toner to the surface of the photoconductor 21. Thereby, the electrostatic latent image on the photoconductor 21 is made visible. Then, the toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer drum 41 of the transfer unit 4 in the primary transfer area TR1.

The cleaning section 24 is located at a position which has advanced from the primary transfer area TR1 in the circumferential direction (the direction of the arrow in FIG. 1).
And scrapes off the toner remaining on the outer peripheral surface of the photoconductor 21 after the primary transfer.

The intermediate transfer drum 41 of the transfer unit 4 rotates while receiving a rotational driving force from a drive motor (not shown) while being in contact with the photosensitive member 21. The configuration for driving the intermediate transfer drum 41 will be described later together with the drive mechanism of the photoconductor 21.

When a color image is to be transferred to a recording material, a color image is formed by superimposing the toner images of each color formed on the photoreceptor 21 on the intermediate transfer drum 41. When transferring a monochrome image to a recording material,
Only a black toner image is formed on the intermediate transfer drum 41 on the photoconductor 21.

The toner image thus carried on the intermediate transfer drum 41 is secondarily transferred to a recording material by a secondary transfer roller 42. This secondary transfer roller 42
Is capable of coming in contact with and separating from the intermediate transfer drum 41, contacts the intermediate transfer drum 41 at an appropriate timing, and transfers toner to the recording material conveyed to the secondary transfer area TR2 along the conveyance path 61. The image is secondarily transferred.

In the vicinity of the secondary transfer area TR2, a cleaning unit 43 is provided so as to be able to contact and separate from the intermediate transfer drum 41.
The toner that is in contact with the intermediate transfer drum 41 at an appropriate timing and remains on the outer peripheral surface of the intermediate transfer drum 41 after the secondary transfer is scraped off by the cleaning unit 43.

Further, a fixing unit 5 is disposed on the downstream side of the secondary transfer area TR2 along the conveyance path 61, and the toner image on the recording material conveyed along the conveyance path 61 is recorded on the recording material. Established in Then, the recording material is further transported along a transport path 61 to a discharge tray (not shown).

Next, the photosensitive member 21 and the intermediate transfer drum 4
A configuration for rotating the drive 1 will be described with reference to FIGS. FIG. 2 is a partial perspective view of the image forming apparatus of FIG.

As shown in FIG. 2, the drum driving gear 8 is rotated on the rotation shaft 411 of the intermediate transfer drum 41 by the intermediate transfer drum 41.
The intermediate transfer drum 41 receives the rotational driving force from the drive motor directly or via a speed reduction mechanism, and rotates about the rotation shaft 411. Also, the photoconductor 21
The photoreceptor drive gear 9 is fixed to the photoreceptor 21 in a state of being meshed with the drum drive gear 8 on the rotating shaft 211. In particular, in this embodiment, the number of teeth of the drum drive gear 8 is Z1.
When the number of teeth of the photoconductor driving gear 9 is Z2, the diameter of the intermediate transfer drum 41 is D1, and the diameter of the photoconductor 21 is D2, the following inequality expression is satisfied: Z2 / Z1> D2 / D1. Is configured. For this reason, the peripheral speed of the intermediate transfer drum 41 becomes faster than the peripheral speed of the photoconductor 21,
The photoconductor 21 does not rotate by directly receiving the rotational driving force from the drive motor, but rotates following the intermediate transfer drum 41.

Here, when the engagement state between the drum driving gear 8 and the photosensitive member driving gear 9 is examined in detail, as shown in FIG.
The rotation-direction tooth surface 91 of the photoconductor driving gear 9 is locked to the anti-rotation direction tooth surface 82 of the drum driving gear 8, and in this locked state, the photoconductor 21 is moved to the intermediate transfer drum as described above. It rotates following 41.

In the image forming apparatus configured as described above,
In order to execute the developing process, one of the four developing devices selectively contacts the photoconductor, and at the time of the contact, the photoconductor 21
Even if an external force acting in the direction of increasing the peripheral speed acts on the photoconductor 21, the drum driving gear 8 functions as a stopper for the photoconductor driving gear 9, and the fluctuation of the peripheral speed of the photoconductor 21 can be prevented. As a result, it is possible to prevent the occurrence of an image defect called so-called banding and to form a good image.

Further, even while the developing device is in contact with the photoconductor 21, an external force acting in a direction to increase the peripheral speed of the photoconductor 21 due to the interaction force between the developing device and the photoconductor 21 is exposed. In this case as well, the drum drive gear 8 functions as a stopper for the photoconductor drive gear 9 in the same manner as described above, so that image defects are prevented from occurring and good image formation is performed. It can be carried out.

Further, in the image forming apparatus, as shown in FIG. 2, a developing unit 23Y for yellow, a developing unit 23M for magenta, a developing unit 23C for cyan, and a developing unit 23K for black have a rotating shaft 231. The developing device is switched by rotating counterclockwise around the center. Therefore, when the developing device is switched, an external force acting in a direction to increase the peripheral speed of the photoconductor 21 may be applied to the photoconductor 21. However, according to this embodiment, even if the external force acts, the drum drive gear 8 functions as a stopper for the photoconductor drive gear 9, and the same operation and effect as described above can be obtained. Thus, it can be said that the present invention is a very useful technique for an image forming apparatus that switches the developing device by a revolver (rotation) method.

The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, in the above embodiment, the present invention is applied to the image forming apparatus that forms a color image by superimposing a toner image on the surface of the intermediate transfer drum 41, but the present invention is not limited to this. is not. For example, the present invention can be applied to an image forming apparatus in which a recording material is wound around the surface of the transfer drum 41 and a toner image is superimposed on the recording material to form a color image.

The present invention is also applicable to an image forming apparatus using an intermediate transfer belt instead of using the intermediate transfer drum 41. In this case, the driving roller and
An intermediate transfer belt is stretched over at least one or more driven rollers, and a belt driving gear is fixed to a driving roller on a rotation shaft of the driving roller while meshing with a photoconductor driving gear 9. On the other hand, a rotational driving force from the driving motor is applied. Therefore, when the number of teeth of the belt drive gear is Z1, the number of teeth of the photoconductor drive gear 9 is Z2, the diameter of the drive roller is D1, and the diameter of the photoconductor 21 is D2, the following inequality: Z2 / Z1 > D2 / D1, the same operation and effect as the above embodiment can be obtained.

In the above description, the peripheral speed of the photoreceptor is varied with reference to the abutment of the developing unit or the interaction force with the developing unit. Although the speed may fluctuate, in this case also, the present invention can prevent the peripheral speed of the photoreceptor from increasing, and the same operation and effect as in the case of the peripheral speed fluctuation by the developing device can be obtained as described above.

Further, the image forming apparatus described above is a printer, but the image forming apparatus includes all image forming apparatuses such as a copying machine and a facsimile machine.

[0031]

According to the first aspect of the present invention, the transfer drum is rotated by rotating the drum driving gear by the driving unit, and the photoconductor is fixed to the photoconductor on the rotation axis of the photoconductor. The drum drive gear meshes with the drive gear. When the number of teeth of the drum drive gear is Z1, the number of teeth of the photoconductor drive gear is Z2, the diameter of the transfer drum is D1, and the diameter of the photoconductor is D2, the following inequality: Z2 / Z1> D2 / D1 is satisfied, so that the photoconductor follows the transfer drum in a state in which the rotation-side tooth surface of the photoconductor drive gear is locked to the anti-rotation side tooth surface of the drum drive gear. Even if external force acting in the direction of increasing the peripheral speed of the photoreceptor acts on the photoreceptor, the drum drive gear functions as a stopper, and the peripheral speed of the photoreceptor can be stabilized. Image can be formed.

According to the second aspect of the present invention, the intermediate transfer belt is rotated by rotating the belt driving gear fixed to the driving roller on the rotation axis of the driving roller by the driving unit, and rotating the belt. A belt drive gear meshes with a photoconductor drive gear fixed to the photoconductor on the rotation axis of the body. Then, the number of teeth of the belt drive gear is set to Z1.
When the number of teeth of the photoconductor driving gear is Z2, the diameter of the driving roller is D1, and the diameter of the photoconductor is D2, the following inequality is satisfied: Z2 / Z1> D2 / D1 Therefore, the peripheral speed of the photoconductor can be stabilized by the stopper function of the belt drive gear, and a good image can be formed, as in the first aspect of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a partial perspective view of the image forming apparatus of FIG.

FIG. 3 is a diagram illustrating an engagement state between a drum driving gear and a photoconductor driving gear.

[Explanation of symbols]

 8: Drum drive gear 9: Photoconductor drive gear 21: Photoconductor 41: Intermediate transfer drum 82: Anti-rotation side tooth surface 91: Rotation direction side tooth surface 211: Rotating shaft (of the photoconductor) 411 (Intermediate transfer drum) A) rotating shaft

Claims (2)

[Claims] 1. An image forming apparatus for transferring a toner image formed on a drum-shaped photoreceptor to a surface of a transfer drum or a recording material wound around the surface, wherein the transfer is performed on a rotation axis of the transfer drum. A drum drive gear fixed to the drum, a photoconductor drive gear fixed to the photoconductor on a rotation axis of the photoconductor, and meshing with the drum drive gear; and a drive unit that rotationally drives the drum drive gear. When the number of teeth of the drum drive gear is Z1, the number of teeth of the photoconductor drive gear is Z2, the diameter of the transfer drum is D1, and the diameter of the photoconductor is D2, the following inequality: Z2 / Z1> D2 / D1. 2. An image forming apparatus for transferring a toner image formed on a drum-shaped photoreceptor to an intermediate transfer belt, comprising: a drive roller that stretches and drives the intermediate transfer belt; and a rotation shaft of the drive roller. A belt drive gear fixed to the drive roller above; a photoconductor drive gear fixed to the photoconductor on the rotation axis of the photoconductor and meshing with the belt drive gear; and rotating the belt drive gear. When the number of teeth of the belt driving gear is Z1, the number of teeth of the photoconductor driving gear is Z2, the diameter of the driving roller is D1, and the diameter of the photoconductor is D2, An image forming apparatus satisfying the following inequality: Z2 / Z1> D2 / D1.