Light deflection unit, optical scanning apparatus, and image forming apparatus

摘要

The light deflection unit including a rotary member having 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, in which a mass of the rotor frame is largest among masses of a plurality of members forming the rotary member, the mass of the rotor frame is smaller than 3 g, and a thickness of the plate of metal 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 becomes smaller than a fatigue limit of the metal.

主权项

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 2R1[mm], an inner diameter of a cylindrical surface formed by a distal end of the inward-looking flange portion is represented by 2R2 [mm], a distance from the inward-looking flange portion to the outward-looking flange portion in an axial direction of the rotor frame is represented by L1 [mm], a length of the outward-looking flange portion in a radial direction of the rotor frame is represented by L2 [mm], a length of the bent-back portion in the axial direction of the rotor frame is represented by L3 [mm], and a specific gravity of the rotor frame is represented by ρ1 [g/mm3],t<3π×{2⁢R1⁢L1+2⁢(R1+L2)⁢L3+(R1+L2)2-R22}×ρ1 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.