Patent ID: 7711300

Claim:
An image forming apparatus, comprising: an image carrier configured to travel in an endless loop and including a surface configured to bear a visible image; an endless transfer-fixing belt stretchedly arranged between at least two spanning members, wherein the endless transfer-fixing belt has a substantially flat front surface formed between the at least two spanning members, the endless transfer-fixing belt being configured to contact the image carrier via the front surface to form a transfer nip while contacting another member other than the image carrier to form a transfer-fixing nip; a pressure member configured to press the front surface of the transfer-fixing belt to the image carrier while contacting a backside of the front surface of the transfer-fixing belt at the transfer nip, the pressure member being located between the at least two spanning members relative to the backside of the front surface of the transfer-fixing belt; and a heater configured to heat the visible image; the image carrier is further configured to transfer the visible image onto the front surface of the transfer-fixing belt at the transfer nip, and the transfer-fixing belt is further configured to transport the visible image to the transfer-fixing nip while heated by the heater, and to transfer and fix the visible image on a recording member; and the transfer-fixing belt is stretchedly arranged such that the transfer-fixing belt travels in a direction substantially perpendicular to a pressure direction of the pressure member in a proximity of the transfer nip, wherein the pressure member comprises a curved surface having a curvature and contacting the transfer-fixing belt, and the image forming apparatus is further configured to satisfy the following relationship: T 1 sin θ 1 +T 2 sin θ 2 <2.5 ×S, wherein θ 1 is an angle between a first virtual line segment L 1 extending from a winding start point P 1 of the transfer-fixing belt relative to the curved surface of the pressure member to a center of a virtual circle having the same curvature as that of the curved surface, the virtual circle being drawn along a curved direction of the curved surface, and a third virtual line segment L 3 extending from the center point of the transfer nip in a belt traveling direction of the transfer-fixing belt to the center of the virtual circle; θ 2 is an angle between a second line segment L 2 extending from a winding finish point P 2 of the transfer-fixing belt relative to the pressure member to the center of the virtual circle and the third line segment L 3 ; S is an area of the transfer nip; T 1 is a tension near the winding start point P 1 of the transfer-fixing belt in a resting state; and T 2 is a tension near the winding finish point P 2 of the transfer-fixing belt in the resting state.