Fixing device having stably positioned nip plate

A fixing device for thermally fixing a developing agent image to a sheet comprising:

• a flexible tubular member having an inner peripheral surface defining an internal space, the flexible tubular member defining an axis extending in an axial direction;
• a heater disposed at the internal space;
• a nip plate disposed at the internal space and having a first surface configured to be in sliding contact with the inner peripheral surface of the flexible tubular member and a second surface opposite to the first surface, the nip plate being formed with an engaging portion;
• a backup member configured to nip the flexible tubular member in cooperation with the first surface of the nip plate, the backup member confronting the first surface of the nip plate in a first direction;
• a stay extending in the axial direction and configured to cover the heater and support the nip plate, the stay providing an opening facing toward the nip plate and having an end portion in the axial direction, the stay comprising:
• a support portion configured to support the second surface of the nip plate;
• a plurality of hook portions provided at the end portion and configured to support the first surface of the nip plate;
• and
• a protruding portion protruding in the first direction toward the backup member and configured to engage the engaging portion such that the nip plate is restricted from moving in a direction orthogonal to the first direction;
• and
• a biasing member configured to bias the nip plate toward the backup member,
• wherein the sheet is conveyed in a sheet conveying direction that is perpendicular to the axial direction, and
• wherein the nip plate has a first side and a second side opposite to the first side in the sheet conveying direction, the biasing member being positioned at the first side, and the protruding portion being positioned at the second side.

A fixing device comprising:

• an endless belt having an inner peripheral surface defining an internal space, the endless belt extending in an axial direction;
• a heater extending through the internal space of the endless belt;
• a nip plate provided with an engaging portion, the nip plate having:
• a first surface configured to be in contact with the inner peripheral surface of the endless belt;
• and
• a second surface opposite to the first surface;
• a roller, the roller and the nip plate being configured to nip the endless belt therebetween;
• and
• a stay extending through the internal space of the endless belt and having a first end portion and a second end portion opposite to the first end portion in the axial direction, the stay comprising:
• a support portion configured to support the second surface of the nip plate;
• a plurality of hook portions provided at least at the first end portion and configured to support the first surface of the nip plate, each of the plurality of hook portions having a tip end portion that is directed in a direction away from the second end portion in the axial direction;
• and
• a protruding portion protruding in a first direction toward the roller, the protruding portion being configured to engage the engaging portion such that the nip plate is restricted from moving in a direction orthogonal to the first direction.