Patent ID: 7187895

Claim:
A sheet nipping mechanism for accommodating sheets of a plurality of different sizes ranging from a minimum size which is at least as small as a B5 size sheet to a maximum size which is at least as large as an A3 size sheet comprising: a transport device for transporting a sheet having a toner image transferred thereonto through a photosensitive drum; a fixing device including a fixing roller and a pressure roller downstream of the transport device and vertically aligned in a paired manner to define a nip zone therebetween; and a guide member disposed between the nip zone and a downstream end of the transport device, wherein the fixing roller is formed in a reverse-crown shape whose diameter is gradually reduced in a direction extending from each of the opposite transverse ends to the central region of the fixing roller, and the guide member having an upstream edge in opposed relation to the transport device, a downstream edge in opposed relation to a peripheral surface of the fixing roller adjacent to the nip zone, and a sheet-feeding surface extending substantially between the upstream and downstream edges for receiving a sheet transported from the transport device, the sheet-feeding surface including a pair of depressed areas receding from the sheet-feeding surface and formed in opposite transverse edge regions in proximity to the upstream edge thereof, the depressed areas being designed such that when any of the sheets having the different sizes ranging from the minimum size at least small as the B5 size sheet to the maximum size at least as large as the A3 size sheet is fed onto the guide member, opposite transverse edges of the sheet are allowed to be located within a range of the corresponding depressed areas, the downstream edge being formed as a crown-shaped arc edge designed to allow the gap between the peripheral surface and the downstream edge to be set at an approximately constant value over its entire longitudinal length.