Fixing device and image forming apparatus

1. A fixing device comprising:

an endless belt;

a fixing rotating body that contacts with and separates from the belt and fixes, in cooperation with the belt, a toner image formed on a recording medium nipped between the fixing rotating body and the belt while rotating in contact with the belt;

a support member provided on an inner side of the belt so that the belt slides on the support member during circulation, the support member supporting a load with which the fixing rotating body nips the recording medium with the belt so as to form a nip portion where the recording medium is nipped between the belt and the fixing rotating body;

a driving unit that drives the belt so that the belt circulates in a state in which the fixing rotating body is separate from the belt;

a first wind-on rotating body rotatably provided on the inner side of the belt so that the belt is wound on the wind-on rotating body at a position adjacent to the support member on an upstream side in a direction of transport of the recording medium to the nip portion,

a second wind-on rotating body rotatably provided on the inner side of the belt so that the belt is wound on the wind-on rotating body at a position adjacent to the support member on a downstream side in a direction of transport of the recording medium to the nip portion,

wherein, as a result of bending the fixing belt at an obtuse angle at both ends of the nip portion, the angle at one end of the nip portion is different from another end of the nip portion,

wherein a diameter of the first wind-on rotating body gradually decreases from a center toward an end in an axial direction, and

the support member functions as an internal heating source that heats the belt, and which is positioned inside the belt and adjacent to the first-wind on rotating body.

2. The fixing device according to claim 1 , further comprising:

a restraint unit that restrains rotation of the wind-on rotating body in a state in which the fixing rotating body is in contact with the belt.

3. An image forming apparatus comprising:

a toner-image forming unit that forms a toner image on a recording medium;

a transfer device that transfers the toner image formed by the toner-image forming unit onto the recording medium; and

the fixing device according to claim 1 , the fixing device fixing the toner image transferred on the recording medium.

4. An image forming apparatus comprising:

a toner-image forming unit that forms a toner image on a recording medium;

a transfer device that transfers the toner image formed by the toner-image forming unit onto the recording medium; and

the fixing device according to claim 1 , the fixing device fixing the toner image transferred on the recording medium.

5. An image forming apparatus comprising:

a toner-image forming unit that forms a toner image on a recording medium;

a transfer device that transfers the toner image formed by the toner-image forming unit onto the recording medium; and

the fixing device according to claim 2 , the fixing device fixing the toner image transferred on the recording medium.

6. A fixing device comprising:

an endless belt;

a fixing rotating body that contacts with and separates from the belt and fixes, in cooperation with the belt, a toner image formed on a recording medium nipped between the fixing rotating body and the belt while rotating in contact with the belt;

a support member provided on an inner side of the belt so that the belt slides on the support member during circulation, the support member supporting a load with which the fixing rotating body nips the recording medium with the belt so as to form a nip portion where the recording medium is nipped between the belt and the fixing rotating body;

a driving unit that drives the belt so that the belt circulates in a state in which the fixing rotating body is separate from the belt;

a wind-on rotating body rotatably provided on the inner side of the belt so that the belt is wound on the wind-on rotating body at a position adjacent to the support member on an upstream side in a direction of transport of the recording medium to the nip portion,

wherein a restraint unit that restrains rotation of the wind-on rotating body in a state in which the fixing rotating body is in contact with the belt.

7. A fixing device comprising:

an endless belt;

a fixing rotating body that is configured to move towards the belt to make contact with the belt and move away from the belt to separate from the belt and fixes, in cooperation with the belt, a toner image formed on a recording medium nipped between the fixing rotating body and the belt while rotating in contact with the belt;

a support member provided on an inner side of the belt so that the belt slides on the support member during circulation, the support member supporting a load with which the fixing rotating body nips the recording medium with the belt so as to form a nip portion where the recording medium is nipped between the belt and the fixing rotating body;

a driving unit that drives the belt so that the belt circulates in a state in which the fixing rotating body is separate from the belt;

a wind-on rotating body rotatably provided on the inner side of the belt so that the belt is wound on the wind-on rotating body at a position adjacent to the support member on an upstream side in a direction of transport of the recording medium to the nip portion,

wherein a diameter of the wind-on rotating body gradually decreases from a center toward an end in an axial direction, and

the support member functions as an internal heating source that heats the belt, and which is positioned inside the belt and adjacent the wind on rotating body.