Image forming apparatus

Abstract

Provided is an image forming apparatus that forms an image on a recording material, the apparatus including: a first helical gear and a second helical gear that are engaged with each other; and a driving portion that applies a driving force to the first helical gear, wherein at least one of the first helical gear and the second helical gear is a helical gear in which torsional rigidity in a tooth width direction of one side end in a width direction of the gear is larger than torsional rigidity in a tooth width direction of the other side end, and wherein a twist direction of helical teeth and a rotational direction of the first helical gear due to the driving portion are set such that the other side end is engaged earlier than the one side end.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image forming apparatus such as a copying machine or a printer equipped with a function of forming an image on a recording material such as a sheet.

Description of the Related Art

Japanese Patent Laid-Open No. 9-230657 discloses a configuration in which an annular rib is disposed between a central portion and a tooth surface of a gear and the tooth surface and the annular rib are disposed at an interval so as not to come in contact with each other. According to such a configuration, since the tooth surface and the annular rib do not contact with each other, phenomena are suppressed in which a portion of the tooth surface coming in contact with the annular rib is deformed by shrinkage during molding and thus accuracy of the tooth surface deteriorates.

By this configuration, it is considered that variation in a position occurs due to a rotation fluctuation or vibration of an image preparing portion caused by a rotation fluctuation or vibration occurring at a gear engagement cycle and thus a periodic band-like uneven density called a banding image is prevented.

However, the invention disclosed in Japanese Patent Laid-Open No. 9-230657 does not cope with reduction in size of a gear and modules for the purpose of miniaturization of an apparatus body in recent years. It is difficult to make the modules smaller in the case of reducing the size of the gear. This reason is that stress applied to a tooth root of the gear rises when the size of the module becomes smaller.

Under these circumstance, the inventors paid attention to the fact that a portion of an arm formed between the tooth surface and a rotation support portion is disposed at the center of a tooth width direction in the configuration illustrated in FIG. 3 of Japanese Patent Laid-Open No. 9-230657. The inventors found that it is possible to reduce the size of the module and to lower the stress applied to the tooth root of the gear by changing the arrangement of the arm.

SUMMARY OF THE INVENTION

The invention is to provide an image forming apparatus capable of suppressing stress concentration on a tooth root of a gear.

An image forming apparatus that forms an image on a recording material includes: a first helical gear and a second helical gear that are engaged with each other; and a driving portion that applies a driving force to the first helical gear, wherein at least one of the first helical gear and the second helical gear is a helical gear in which torsional rigidity in a tooth width direction of one side end in a width direction of the gear is larger than torsional rigidity in a tooth width direction of the other side end, and wherein a twist direction of helical teeth and a rotational direction of the first helical gear due to the driving portion are set such that the other side end is engaged earlier than the one side end.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating schematically an image forming apparatus according to the invention.

FIG. 2A is a schematic diagram illustrating a state where motors are connected to a photosensitive drum and an intermediate belt unit, respectively, and FIG. 2B is a schematic diagram of a driving configuration of a developing device.

FIG. 3 is a schematic diagram of a gear arrangement in the driving configuration of the developing device illustrated in FIG. 2B.

FIGS. 4A and 4B are perspective views illustrating a developing motor gear and a developing reduction gear in detail.

FIG. 5 is a cross-sectional view of the developing motor gear and the developing reduction gear.

FIGS. 6A to 6F are perspective views illustrating calculation results of a contact state of teeth, respectively.

FIGS. 7A and 7B are numerical value-attached perspective views illustrating maximum stress in a developing reduction gear and calculation results of occurrence points of the maximum stress.

FIG. 8 is a cross-sectional view of a developing motor gear and a developing reduction gear according to a second embodiment.

FIG. 9 is a cross-sectional view of a developing motor gear and a developing reduction gear according to a third embodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, with reference to the drawings, embodiments of the invention will be exemplarily described in detail. However, dimensions, materials, shapes, and relative positions of components described in the embodiments are appropriately changed depending on structures and various conditions of apparatuses to which the invention is applied and therefore the scope of the invention is not intended to be limited thereto unless otherwise particularly specified. In each of the drawings, components denoted by the same reference numerals have the same structure or operation, and the duplication description thereof will not be appropriately presented.

[First Embodiment]

FIG. 1 is a schematic cross-sectional view illustrating schematically an image forming apparatus 50 according to the invention. In the following description, each of the stations denoted by reference numerals with Y, M, C, and K means member for yellow, magenta, cyan, and black, and these members will be described below by reference numerals without signs of Y, M, C, and K. The image forming apparatus 50 illustrated in FIG. 1 is an example of a full-color image forming apparatus (complex machine having all of copying machine, printer function, and FAX function). In FIG. 1, the image forming apparatus 50 has a plurality of image forming stations (four image forming stations in this embodiment) which are transversely juxtaposed with each other in an image forming apparatus body (hereinafter, referred to as an “apparatus body 50A”).

Each of the stations includes a drum-like electrophotographic photosensitive drum (referred to as a “photosensitive drum 10” in this embodiment) as an “image bearing member”. In this embodiment, the photosensitive drums 10 sequentially bear color images of a yellow (Y) component, a magenta (M) component, a cyan (C) component, and a black (K) component, respectively. These photosensitive drums 10 are rotatably driven at a predetermined process speed in an arrow direction “A” (counterclockwise direction) by a drum motor which is not illustrated in the drawing.

For example, a charging device 11, a scanner unit 12, a developing device 13, an intermediate belt unit 14, and a cleaning device 15 are sequentially disposed around each of the photosensitive drums 10 according to a rotational direction of the photosensitive drum 10. The charging device 11 (charging portion) is configured to uniformly charge the surface of the photosensitive drum 10. The scanner unit 12 (exposure portion) is configured to irradiate the photosensitive drum 10 with a laser beam based on image information and form an electrostatic image on the photosensitive drum 10.

The developing device 13 as a “developing portion” is configured to develop the electrostatic image formed on the surface of the photosensitive drum 10 with a toner and generate a developer image (toner image). The intermediate belt unit 14 (electrostatic transfer portion) is configured to transfer the toner image on the photosensitive drum 10 onto a sheet. The cleaning device 15 (cleaning portion) is configured to remove a transfer residual toner remaining on the surface of the photosensitive drum 10 after the transfer.

Hereinafter, the image forming station for yellow (Y) out of four colors will be described as an example. A photosensitive drum 10Y is uniformly subjected to a charging treatment by a charging device 11Y during a rotation process so as to have predetermined polarity and potential. Then, the photosensitive drum 10Y is exposed to light by a laser scanner 12Y, whereby an electrostatic image of image information is formed on the photosensitive drum 10Y.

Next, the electrostatic image formed on the photosensitive drum 10Y is visualized by a developing device Thefeatures of the second embodiment that have features of the third embodiment that have the same configuration as the first embodiment will not be presented.

In this embodiment, the developing reduction gear 104 is formed with a web 104e between a boss 104d and a rim 104c. The web 104e is disposed substantially at the center in the tooth width direction M of the developing reduction gear 104. The web 104e is formed in a disk-like plate shape around the boss 106 104d.

On the premise of this configuration, a rib 104f radially extends from the boss 104d (this is the same as the configuration in FIG. 4B) and protrudes toward a front side 104a from the web 104e (this is different from the configuration in FIG. 4B) at the same time. In this way, the rib 104f is disposed at only the front side 104a (one side) in the tooth width direction M. For this reason, a gradient of torsional rigidity in the tooth width direction M is formed to be large at the front side 104a and to be small at a rear side 104b.

Thus, the torsional rigidity in the tooth width direction M of the developing reduction gear 104 becomes gradually smaller from the front side 104a (one side) toward the rear side 104b (the other side) in the tooth width direction M. In other words, the torsional rigidity in the tooth width direction M becomes gradually smaller from a side disposed with the rib 104f toward a side not disposed with the rib 104f. For this reason, it is also considered that the torsional rigidity in the tooth width direction M at the side not disposed with the rib 104f is smaller than the torsional rigidity in the tooth width direction M at the side disposed with the rib 104f.

According to any one configuration of the first to third embodiments, it is possible to suppress stress concentration on a gear tooth root even when the module is reduced compared to the related art.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2014-221347, filed Oct. 30, 2014, which is hereby incorporated by reference herein in its entirety.

Claims

1. An image forming apparatus that forms an image on a recording material, the image forming apparatus comprising:

a first photosensitive drum;

a second photosensitive drum;

a first driving motor configured to generate a driving force to be transferred to the first photosensitive drum and the second photosensitive drum;

a first gear;

a first developing portion connected to the first gear, the first developing portion being configured to develop an electrostatic image on the first photosensitive drum with a toner and rotate in a case where a driving force is transferred to the first gear;

a second gear;

a second developing portion connected to the second gear, the second developing portion being configured to develop an electrostatic image on the second photosensitive drum with a toner of color different from the toner of the first developing portion and rotate in a case where a driving force is transferred to the second gear; and

a driving force transfer unit configured to transfer a driving force to the first gear and the second gear, the driving force transfer unit including:

(A) a first helical gear including a plurality of teeth; and

(B) a second driving motor configured to generate a driving force for rotating the first helical gear and connected to the first helical gear to transmit the driving force of the second driving motor to the first helical gear; and

(C) a second helical gear that is engaged and a third gear which transfer the driving force of the second driving motor to the first gear and the second gear, the second helical gear configured to engage with the first helical gear, the second helical gear having a first side and a second side with respect to an axis direction of the second helical gear the third gear rotating coaxially with the second helical gear and configured to engage with the first gear and the second gear, each of the third gear and the second helical gear having a diameter, the diameter of the third gear being smaller than the diameter of the second helical gear, the second helical gear including:

(a) a rim that has including an outer circumference formed with a plurality of teeth, configured to engage with the plurality of teeth of the first helical gear, the second helical gear including a first side relative to a center of the rim in a tooth width direction of the second helical gear and a second side relative to the center of the rim in the tooth width direction of the second helical gear;

(b) a boss that is a center of rotation of the rim, and second helical gear;

(c) a web through which (i) disposed at the first side and (ii) connecting the rim and the bossof the second helical gear are connected to each other,;

(d) a concentric rib (i) projecting from the web to the second side in the tooth width direction and (ii) being concentric with the boss; and

(e) a plurality of radial ribs (i) projecting from the web to the second side in the tooth width direction, (ii) extending from the boss in a radial fashion so as to connect the boss and the concentric rib, and (iii) disposed apart from the rim in a radial direction of the second helical gear,

wherein the web is disposed so as to be shifted toward the first side, and the plurality of teeth of the second helical gear is configured so that a region of each of the plurality of teeth at the second side of the second helical gear engages with the first helical gear earlier than when another region of each of the tooth teeth at the first side of the second helical gear engages with the first helical gear.

2. The image forming apparatus according to claim 1, wherein a torsional rigidity of the second side of the second helical gear is smaller than a torsional rigidity of the first side of the second helical gear.

3. The image forming apparatus according to claim 1, wherein a thickness of the rim at the second side of the second helical gear is less than a thickness of the rim at the first side of the second helical gear.

4. The image forming apparatus according to claim 1, wherein the second helical gear includes a plurality of ribs that protrude in the axis direction from a face of the web and extend radially from the boss, such that each rib is exposed to only the second side of the second helical gear and is not exposed to the first side of the second helical gear, and a torsional rigidity of the second side of the second helical gear is smaller than a torsional rigidity of the first side of the second helical gear.

5. The image forming apparatus according to claim 1, wherein the second helical gear is formed of a resin and the first helical gear is formed of a metal.

6. The image forming apparatus according to claim 5, wherein the number of teeth of the first helical gear is set to be smaller than the number of teeth of the second helical gear.

7. The image forming apparatus according to claim 6, further comprising: a wherein the second driving motor that applies a driving force to the first helical gear includes a driving shaft, and

wherein the first helical gear is subjected to gear cutting together with a formed by teeth cut directly on the driving shaft of the motor.

8. The image forming apparatus according to claim 7, further comprising:

an image bearing member; and

a developing portion that develops an electrostatic image on a surface of the image bearing member with a toner,

wherein the motor that applies the driving force to the first helical gear drives the developing portion.

9. The image forming apparatus according to claim 1, wherein the web has first and second outer surfaces with respect to the axis direction of the second helical gear, the first and second outer surfaces of the web being positioned at the first side of the second helical gear deviated from a center of the second helical gear in the axis direction.

10. An image forming apparatus that forms an image on a recording material, the image forming apparatus comprising:

a first helical gear; and

a second helical gear that is engaged with said first helical gear, the second helical gear having a first side and a second side with respect to an axis direction of the second helical gear, the second helical gear including a plurality of teeth formed at an outer peripheral surface thereof and a wall portion formed at an inner peripheral surface thereof toward a rotation center of the second helical gear, the wall portion being formed continuously along the inner peripheral surface of the second helical gear,

wherein the wall portion is disposed so as to be shifted toward the first side from a center with respect to the axis direction of the second helical gear, and the plurality of teeth of the second helical gear is configured so that a region of each of the plurality of teeth at the second side of the second helical gear engages with the first helical gear earlier than when another region of the tooth at the first side of the second helical gear engages with the first helical gear.

11. The image forming apparatus according to claim 10, wherein the wall portion has first and second outer surfaces with respect to the axis direction of the second helical gear, the first and second outer surfaces of the wall portion being positioned at the first side of the second helical gear deviated from a center of the second helical gear in the axis direction.

12. The image forming apparatus according to claim 11, wherein the wall portion is disposed at an end portion of the second helical gear in the axis direction of the second helical gear.

13. The image forming apparatus according to claim 1, wherein, in a direction of the diameter of the second helical gear, no rib is disposed between the concentric rib and the rim.

14. The image forming apparatus according to claim 1, wherein in a direction of the diameter of the second helical gear, a distance between the boss and the concentric rib is larger than a distance between the concentric rib and the rim.

15. The image forming apparatus according to claim 1, wherein, in the tooth width direction of the second helical gear, a projecting dimension of the boss from the web is larger than a projecting dimension of the plurality of radial ribs from the web.

16. An image forming apparatus that forms an image on a recording material, the image forming apparatus comprising:

a first photosensitive drum;

a second photosensitive drum;

a first driving motor configured to generate a driving force to be transferred to the first photosensitive drum and the second photosensitive drum;

a first gear;

a first developing portion connected to the first gear, the first developing portion being configured to develop an electrostatic image on the first photosensitive drum with a toner and rotate in a case where a driving force is transferred to the first gear;

a second gear;

a second developing portion connected to the second gear, the second developing portion being configured to develop an electrostatic image on the second photosensitive drum with a toner of color different from the toner of the first developing portion and rotate in a case where a driving force is transferred to the second gear; and

a driving force transfer unit configured to transfer a driving force to the first gear and the second gear, the driving force transfer unit including:

(A) a first helical gear including a plurality of teeth formed thereon;

(B) a second driving motor configured to generate a driving force for rotating the first helical gear and connected to the first helical gear to transmit the driving force of the second driving motor to the first helical gear; and

(C) a second helical gear and a third gear which transfer the driving force of the second driving motor to the first gear and the second gear, the second helical gear configured to engage with the first helical gear, the third gear rotating coaxially with the second helical gear and configured to engage with the first gear and the second gear, each of the third gear and the second helical gear having a diameter, the diameter of the third gear being smaller than the diameter of the second helical gear, the second helical gear including:

(a) a rim including an outer circumference formed with a plurality of teeth configured to engage with the plurality of teeth of the first helical gear;

(b) a boss that is a center of rotation of the second helical gear;

(c) a web (i) disposed at one side relative to a center of the rim in a tooth width direction of the second helical gear and (ii) connecting the rim and the boss;

(d) a concentric rib (i) projecting from the web to another side in the tooth width direction and (ii) being concentric with the boss; and

(e) a plurality of radial ribs (i) projecting from the web to the another side in the tooth width direction, (ii) extending from the boss in a radial fashion so as to connect the boss and the concentric rib, and (iii) disposed apart from the rim,

wherein the first helical gear and the second helical gear rotate to transfer the driving force of the second driving motor to the first gear and the second gear so that a contact portion between the teeth of the first helical gear and the teeth of the second helical gear shifts from the another side in the tooth width direction to the one side.

17. The image forming apparatus according to claim 16, wherein a twist direction of the teeth of the first helical gear, a twist direction of the teeth of the second helical gear, a rotary direction of the first helical gear, and a rotary direction of the second helical gear are configured so that an area of the another side in the tooth width direction of the second helical gear is contacted earlier than an area of the one side in the tooth width direction of the second helical gear.

18. The image forming apparatus according to claim 16, wherein a torsional rigidity of the second helical gear in the tooth width direction where the first helical gear and the second helical gear begin to be engaged is smaller than a torsional rigidity of the second helical gear in the tooth width direction where the web is disposed.

19. The image forming apparatus according to claim 16, wherein the second helical gear is formed of a resin and the first helical gear is formed of a metal.

20. The image forming apparatus according to claim 16, wherein a number of teeth of the first helical gear is smaller than a number of teeth of the second helical gear.

21. The image forming apparatus according to claim 16, wherein the second driving motor includes a driving shaft, and

wherein the first helical gear is formed by teeth cut directly on the driving shaft.

22. The image forming apparatus according to claim 16, wherein, in a direction of the diameter of the second helical gear, no rib is disposed between the concentric rib and the rim.

23. The image forming apparatus according to claim 16, wherein, in a direction of the diameter of the second helical gear, a distance between the boss and the concentric rib is larger than a distance between the concentric rib and the rim.

24. The image forming apparatus according to claim 16, wherein, in the tooth width direction of the second helical gear, a projecting dimension of the boss from the web is larger than a projecting dimension of the plurality of radial ribs from the web.