Photosensitive Unit and Image Forming Apparatus

A photosensitive unit comprising:

• a frame;
• a plurality of photosensitive drums which are held by the frame to be in parallel with each other and arranged in a predetermined direction, and on which electrostatic images are formed, respectively;
• a plurality of chargers which are provided so as to oppose the photosensitive drums, respectively, and charge the corresponding photosensitive drums, respectively;
• and
• a plurality of cartridges which are detachably mounted in the frame, each of the cartridges including:
• a developing roller configured to develop an electrostatic latent image by supplying developer to the corresponding photosensitive drum,
• a supply roller supplying developer to the developing roller, and
• a casing including:
• a first casing portion which rotatably supports the developing roller and the supply roller, and includes a first wall opposing the developing roller and the supply roller;
• a second casing portion which stores developer, and includes a second wall;
• and
• a first stepped portion which connects the first casing portion and the second casing portion such that the first wall protrudes further than the second wall,
• wherein the frame includes:
• a pair of side parts including a first side part and a second side part, the first side part and the second side part which are provided on both sides of the photosensitive drums in a longitudinal direction of the photosensitive drums, and rotatably support the photosensitive drums;
• a plurality of beam members which are provided between the first and second side parts, and hold the chargers, respectively;
• and
• an opening formed at an opposite side of the photosensitive drums in a direction orthogonal to the predetermined direction and the longitudinal direction, and through which the cartridges are detachably mounted in the frame,
• wherein each of the first and second side parts includes a plurality of guide grooves, each of which extends from the opening toward a downstream side in a mounting direction, along which the cartridge is mounted in the frame, each of the guide grooves being configured to guide the developing roller of the cartridge to be mounted, toward the corresponding photosensitive drum,
• wherein each of the guide grooves includes at least
• a first portion which is provided at a downstream end in the mounting direction and extends toward a rotation center of the corresponding photosensitive drum as directing to the downstream side in the mounting direction;
• and
• a second portion which is provided at an upstream side in the mounting direction and extends from the opening in a direction intersecting an extending direction of the first portion, toward the downstream side in the mounting direction, and
• wherein each of the beam members includes:
• a third wall which, in a state where the corresponding cartridge is mounted in the frame, opposes the first wall of the cartridge with a first distance therebetween;
• a fourth wall which, in the state where the corresponding cartridge is mounted in the frame, opposes the second wall of the cartridge with a second distance therebetween;
• and
• a second stepped portion which connects the third wall and the fourth wall such that, in the state where the corresponding cartridge is mounted in the frame, the fourth wall protrudes further toward the cartridge than the third wall.