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.

What is claimed is: 
     
       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.