| 摘要 |
PURPOSE:To prevent intrusion of foreign matters into a substantially sealed structure, which accommodates an optical scanning unit. CONSTITUTION:A sack 14 made of a resilient substance is installed in a casing 12 accommodating a polygonal mirror 5 and a motor consisting of a rotor 4, magnet 6, and coil 7, and inside of this sack 14 is led to inside of the casing 12 through a draft tube 12a. This allows holding the gas in the casing 12 at the same pressure as the outside air, so that no outside air will intrude even when the temp. has sunk. |
