Image forming apparatus including common drive source for driving developing roller and cam that moves developing roller toward and away from photosensitive drum

An image forming apparatus comprising:

• a photosensitive drum;
• a developing roller;
• a cam for moving the developing roller between a contacting 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 developing motor for driving both the developing roller and the cam, the developing motor being rotatable in a normal rotating direction and a reverse rotating direction;
• a first transmission mechanism configured to:
• engage power transmission from the developing motor to the developing roller when the developing motor rotates in the normal rotating direction;
• and
• disengage the power transmission from the developing motor to the developing roller when the developing motor rotates in the reverse rotating direction;
• and
• a second transmission mechanism capable of engaging power transmission from the developing motor to the cam, irrespective of whether the developing motor rotates in the normal rotating direction or in the reverse rotating direction.