Patent ID: 7477280

Claim:
An image forming apparatus comprising: a light source that receives printing data to generate a scanning beam; a polygon mirror that receives the scanning beam and that scans the scanning beam in a predetermined width; a reflection mirror that reflects the scanned beam; a blocking member that moves between a blocking position blocking the scanning beam and a non-blocking position allowing the scanning beam to pass; a developing cartridge comprising a photosensitive body that receives the scanning beam reflected by the reflection mirror, wherein the developing cartridge is removably mounted in the image forming apparatus and wherein the developing cartridge interacts with the blocking member to move the blocking member when the developing cartridge is installed into or removed from the image forming apparatus; a sensor interposed between the polygon mirror and the reflection mirror to detect the scanning beam when the scanning beam is not blocked by the blocking member; and a controller that determines whether the developing cartridge is mounted in the image forming apparatus based on whether the scanning beam is detected by the sensor.