POLYGONAL MIRROR

PURPOSE:To enable high-speed rotation with a simple construction by superposing a rotor core consisting of a disk-shaped permanent magnet or secondary conductor and flat plate-shaped ceramic plate having a regular polygonal-shaped outer peripheral edge and forming the outer peripheral edge of the ceramic plates as a mirror part. CONSTITUTION:The ceramic plate 60 consisting of SiC which is hard ceramics is used as a main part and the outer peripheral edge 61 thereof is formed to a regular polygonal shape. The mirror part 66 is formed of the outer peripheral edge 61 as a reflection mirror. The mirror part 66 is formed by forming a coating layer consisting of a metallic material such as aluminum having a high reflectivity on the outer peripheral edge 61 of the ceramic plate 60 and finishing the surface thereof by grinding to a specular surface. The disk-shaped permanent magnet 75 is integrally provided to the ceramic plate 60 and is magnetized with plural magnetic poles to an annular shape along the plane orthogonal with a rotary shaft 62. The rotor core 71 is formed of the permanent magnet 75 and a yoke 73. The polygonal part where air resistance is large is thereby made into the thin construction. Since the rotor core has the disk shape, the air resistance thereof is small.