| 摘要 |
PURPOSE:To realize a silent operation by arranging flat plate type projections at slight distance inside from each side on one or both bottom surfaces of a polygon, and providing gap parts where wind flows in an outward radial direction from the center part nearby respective vertexes. CONSTITUTION:When a polygon mirror 5 rotates together with a rotor 1 integrally, a flow in an outward radial direction from the center is generated in the vicinity of the free surface 7 of the polygon mirror 5. Projections 6 are arranged nearby the outer periphery of the polygon mirror 5 and the gap parts 7b are formed nearby the vertexes 7a of the polygon constituting the free surface 7 of the mirror 5 without providing any projection part, so the flow generated on the free surface extends to the free space of the outer peripheral part through the gaps parts. This flow is accompanied by a secondary flow, but there is not any rotary part which intersects the secondary flow. Consequently, any unnecessary whistling sound is not generated and silent operation is performed. |
