Image forming apparatus including cam having compact structure capable of detection of contact state and separated state of developing roller relative to photosensitive drum

An image forming apparatus comprising:

• a photosensitive drum;
• a developing roller movable between a contact position where the developing roller is in contact with the photosensitive drum and a separated position where the developing roller is separated from the photosensitive drum;
• a clutch configured to control rotation of the developing roller;
• a separation mechanism configured to move the developing roller between the contact position and the separated position, the separation mechanism comprising a cam rotatable about a rotation axis extending in an axial direction, the cam comprising:
• a gear having an outer peripheral surface provided with gear teeth, a first surface and a second surface opposite to the first surface in an axial direction of the gear;
• an end cam disposed at the first surface of the gear in the axial direction of the gear, the end cam being configured to move the developing roller between the contact position and the separate position;
• a phase detection wall disposed at the first surface of the gear and having a hollow cylindrical shape, the phase detection wall having a first slit and a second slit, the first slit and the second slit having a size in the circumferential direction different from each other;
• and
• a plate cam disposed at the second surface of the gear, the plate cam being configured to operate the clutch;
• and
• a detector configured to detect the first slit and the second slit,
• wherein, when the end cam positions the developing roller at the separated position, the detector detects the first slit, and
• wherein, when the end cam positions the developing roller at the contact position, the detector detects the second slit.