Belt unit and image forming apparatus

1. A belt unit, comprising:

(a) a belt member that is stretched by a plurality of rollers in a manner freely travelable;

(b) a cleaning member that is arranged with a tip thereof being in contact with the belt member and scrapes off a developer being attached and carried on the belt member as the belt member travels;

(c) a waste developer accommodation chamber that accommodates the developer as a waste developer scraped off by the cleaning member;

(d) a waste developer carrying member that is rotatably arranged in the waste developer accommodation chamber and carries the waste developer accommodated in the waste developer accommodation chamber in correspondence with a rotation thereof, and

(e) a waste developer taking-up member that

is composed with a shaft and a brush attached to the shaft such that the waste developer taking-up member makes a rotation around the shaft, and

is arranged adjacent to the waste developer carrying member in the waste developer accommodation chamber, wherein

in correspondence with the rotation of the waste developer taking-up member, the waste developer taking-up member

is in physical contact with the waste developer carrying member,

takes up the waste developer from the waste developer carrying member, and

supplies the waste developer to a contact portion between the cleaning member and the belt member.

2. The belt unit according to claim 1 , wherein

the brush overlaps with the waste developer carrying member.

3. The belt unit according to claim 1 , wherein

the brush overlaps with a bottom wall of the waste developer accommodation chamber.

4. The belt unit according to claim 3 , wherein

the bottom wall of the waste developer accommodation chamber includes wall parts that respectively surround a lower half part of the waste developer carrying member and a lower half part of the waste developer taking-up member, and

these lower half parts are determined with respect to a vertical direction, which is parallel to the direction of gravity.

5. The belt unit according to claim 1 , wherein

the brush overlaps with the belt member.

6. The belt unit according to claim 1 , wherein

a support member is arranged on a back side of the belt member, which is opposite to the waste developer carrying member, and applies a reaction force to the belt member such that the belt member does not deform.

7. The belt unit according to claim 1 , wherein

the brush is attached in a spiral shape around the shaft.

8. An image forming apparatus, comprising:

(a) the belt unit according to claim 1 ; and

(b) an image forming unit that has an image carrier and forms a developer image on the image carrier, wherein

(c) the developer image is transferred to a medium carried along with traveling of the belt member.

9. An image forming apparatus, comprising:

(a) the belt unit according to claim 1 ; and

(b) an image forming unit that has an image carrier and forms a developer image on the image carrier, wherein

(c) the developer image is transferred to the belt member.

10. The belt unit according to claim 1 , wherein

the waste developer taking-up member and the waste developer carrying member satisfy following (1) and (2):

OL 1 =Rb−Ra   (1)

OL 1>0  (2)

where Rb is a rotation radius of the waste developer taking-up member, and

Ra is a rotation radius of the waste developer carrying member.

11. The belt unit according to claim 10 , wherein

Rb and OL 1 satisfy following (3):

0.3≤ OL 1/ Rb≤ 0.5  (3).

12. A belt unit, comprising:

(a) a belt member that is stretched by a plurality of rollers in a manner freely travelable;

(b) a cleaning member that is arranged with a tip thereof being in contact with the belt member and scrapes off a developer being attached and carried on the belt member as the belt member travels;

(c) a waste developer accommodation chamber that accommodates the developer as a waste developer scraped off by the cleaning member;

(d) a waste developer caring member that is rotatably arranged in the waste developer accommodation chamber and carries the waste developer accommodated in the waste developer accommodation chamber in correspondence with a rotation thereof; and

(e) a waste developer taking-up member that is rotatably arranged adjacent to the waste developer carrying member in the waste developer accommodation chamber, and takes up the waste developer in correspondence with a rotation thereof and supplies the waste developer to a contact portion between the cleaning member and the belt member, wherein

(f) the waste developer taking-up member is composed with a shaft and a brush attached to the shaft, and

a winding pitch number of the brush is set to an integer multiple with respect to a width of the belt member.

13. The belt unit according to claim 12 , wherein

the winding pitch number of the brush is set to be one with respect to the width of the belt member.