Patent ID: 9523851
Filing Date: 2016-12-20
CPC Classification: G02B,G03G

Claim Text:
1. A light deflection unit comprising a rotary member, wherein the rotary member comprises: a rotor frame formed of a plate of a metal; and a rotary polygon mirror configured to rotate together with the rotor frame and deflect a light beam emitted from a light source, wherein a mass of the rotor frame is largest among masses of a plurality of members forming the rotary member, wherein the mass of the rotor frame is smaller than 3 [gram], wherein the rotor frame comprises a frame main body portion having a cylindrical shape, an inward-looking flange portion extending radially inward from one end of the frame main body portion, an outward-looking flange portion extending radially outward from another end of the frame main body portion, and a bent-back portion having a cylindrical shape and extending from a distal end of the outward-looking flange portion toward the one end side of the frame main body portion, wherein when the thickness of the plate of the metal is represented by t mm , an inner diameter of the frame main body portion is represented by 2R is satisfied, and wherein the thickness t of the plate is set within a range in which a stress amplitude of a portion of the rotor frame on which a largest stress is exerted during rotation of the rotor member is smaller than a fatigue limit of the metal.