Driving device and image forming apparatus

1. A driving device comprising:

a first rotation member having a first rotation axis, said first rotation member including a plurality of roller parts arranged coaxially with each other and in an axial direction of said first rotation axis, a total number of said roller parts being in a range from 4 to 10;

a second rotation member having a second rotation axis;

a stretched member stretched around the first rotation member and the second rotation member, outer surfaces of the roller parts contacting an inner surface of the stretched member;

a shaft shifting member provided on at least one end of said first rotation member, said shaft shifting member being configured to shift at least one end of said first rotation axis in accordance with a movement of said stretched member in said axial direction of said first rotation axis, said shaft shifting member being provided on a first end of said first rotation member;

a pulley provided between said shaft shifting member and said first rotation member;

a first regulating member provided between said pulley and said first rotation member, said first regulating member regulating a movement of said first rotation member in said axial direction;

a second regulating member provided on a second end of said first rotation member, said second regulating member regulating the movement of said first rotation member in said axial direction; and

a spacer provided on an outer side of said second regulating member, said spacer regulating the movement of said first rotation member in said axial direction.

2. The driving device according to claim 1 , wherein a gap is formed between adjacent roller parts of said plurality of roller parts.

3. The driving device according to claim 1 , wherein at least one of said plurality of roller parts includes:

a stretching portion around which said stretched member is stretched, and

at least one abutting portion protruding from said stretching portion in said axial direction of said first rotation axis.

4. The driving device according to claim 3 , wherein said abutting portion has an outer diameter smaller than an outer diameter of said stretching portion.

5. The driving device according to claim 1 , wherein said first rotation member has a shape such that an outer diameter at a center of said first rotation member is larger than an outer diameter of each end of said first rotation member.

6. The driving device according to claim 1 , wherein said first rotation member has a tapered shape such that an outer diameter of said first rotation member decreases from a center to both ends.

7. The driving device according to claim 1 , wherein said shaft shifting member has a third rotation axis inclined with respect to said first rotation axis of said first rotation member, and rotates about said third rotation axis so as to shift said first rotation axis of said first rotation member.

8. The driving device according to claim 1 , wherein said pulley has a contact portion contacting said stretched member, wherein said pulley moves in said axial direction of said first rotation axis to cause said contact portion to contact said stretched member in accordance with a rotation of said shaft shifting member.

9. The driving device according to claim 8 , wherein said pulley includes a flange, and said flange has a tapered portion.

10. The driving device according to claim 1 , wherein said second rotation member includes a driving roller for driving said stretched member.

11. The driving device according to claim 1 , wherein said stretched member includes an endless belt.

12. An image forming apparatus comprising:

said driving device according to claim 1 ;

an image forming portion that forms a developer image; and

a fixing portion that fixes said developer image to a medium.

13. The driving device according to claim 1 , wherein each of the roller parts has an outermost surface touching the stretched member.

14. The driving device according to claim 13 , wherein the roller parts include all rollers covered by the stretched member.

15. The driving device according to claim 1 , wherein the roller parts constitute a divided roller.

16. The driving device according to claim 1 , wherein

said first regulating member is provided at a distance from said pulley.

17. The driving device according to claim 16 , wherein when said stretched member moves in said axial direction of said first rotation axis, said pulley moves together with said stretched member, and said distance between said pulley and said first regulating member changes.

18. The driving device according to claim 1 , wherein said first rotation member includes a larger-diameter part and a smaller-diameter part that has a smaller diameter than that of the larger-diameter part,

wherein said first regulating member regulates the movement of said first rotation member in said axial direction at said larger-diameter part,

wherein said second regulating member regulates the movement of said first rotation member in said axial direction at said smaller-diameter part.

19. The driving device according to claim 1 , wherein said first regulating member is provided only on said first end of said first rotation member,

wherein said second regulating member and said spacer are provided only on said second end of said first rotation member.

20. The driving device according to claim 19 , wherein said first regulating member and said second regulating member have identical shapes, and

wherein said spacer has a different shape from the shapes of said first regulating member and said second regulating member.

21. The driving device according to claim 1 , wherein a distance from one end of said plurality of roller parts to another end of said plurality of roller parts is shorter than a width of said stretched member.