Fuser device having belt supporting part and image forming apparatus having the same

A fuser device for fusing a developer image on a medium by applying heat, comprising:

• an endless fuser belt,
• a belt supporting part that has a first contact face shaped in an arc that is contact with an inner circumferential face of the fuser belt, and a first central position that is a center of the first contact face shaped in the arc,
• a driven ring that is disposed on at least one side of the fuser belt in the width direction of the fuser belt, and
• a ring supporting part that has a second contact face shaped in an arc that is contact with an inner circumferential face of the driven ring, a second central position that is a center of the second contact face shaped in the arc, wherein
• the first central position is shifted from the second central position,
• the ring supporting part is a groove part formed adjacent to the belt supporting part in the with direction of the fuser belt, and
• the depth of the groove part varies along a circumferential direction.

A fuser device for fusing a developer image on a medium by applying heat, comprising:

• an endless fuser belt that is flexible and has a width in a belt axis, the width being determined by a pair of edges in an axis direction along the belt axis wherein the fuser belt has an inner circumferential face and an outer circumferential face that are opposed in a radial direction perpendicular to the axis direction,
• a pair of belt supporting parts each of which has a first contact face shaped in an arc centering on a first central axis, wherein the first central axis being a virtual line extending parallel to the axis direction, wherein the first contact face is inserted inside the fuser belt from one of the edges such that the first contact face supports the inner circumferential face of the fuser belt to rotate around the first central axis,
• a driven ring that has a ring shape, wherein the driven ring has an inner radial, an outer radial, an inside face that is determined by a difference between the inner radial and the outer radial in the radial direction, and the inside face is disposed to face one of the edges of the fuser belt,
• a ring supporting part that has a second contact face shaped in an arc centering on a second central axis, wherein the second central axis being a virtual line extending parallel to the first central axis, wherein the second contact face has a supporting radial in the radial direction from the second central axis, wherein the supporting radial of the ring supporting part is smaller than the inner radial of the driven ring such that the driven ring rotates around the second central axis as contacting the second contact face of the ring supporting part, wherein
• a gap distance, which is defined between the first central axis and the second central axis seen from a view of the belt axis, the inner and outer radials of the driven ring are set such that the inside face of the driven ring is always in contact with the one of the edges of the fuser belt while the fuser belt rotates around the first central axis.