US-12617215-B2 - Optical scanning apparatus and image forming apparatus

US12617215B2US 12617215 B2US12617215 B2US 12617215B2US-12617215-B2

Abstract

An optical scanning apparatus includes a semiconductor laser, a coupling lens, a polygon mirror, a motor, an optical scanning system including a first scanning lens with an optical surface, a housing, a cover, and a partition with an opening closed with the first scanning lens. Shifting amounts of a focus position of a beam with respect to a reference imaging plane in a main scanning direction are in relations ΔA<0 and ΔA<ΔB<ΔC, where ΔA mm and ΔB mm are shifting amounts when the semiconductor laser, the coupling lens, and the optical scanning system are at a normal ambient temperature and at an upper-limit ambient temperature, respectively, and ΔC mm is a shifting amount when the semiconductor laser and the coupling lens are at the normal ambient temperature and the first scanning lens is at a first temperature.

Inventors

Hiroyuki Ominato
Hidetaka Hoshino

Assignees

BROTHER KOGYO KABUSHIKI KAISHA

Dates

Publication Date: 20260505
Application Date: 20240325
Priority Date: 20230403

Claims (10)

1 . An optical scanning apparatus, comprising: a semiconductor laser; a coupling lens made of resin, the coupling lens having a diffractive optical element on at least one surface thereof, the coupling lens being configured to convert light emitted from the semiconductor laser into a beam; a polygon mirror configured to deflect the beam into a main scanning direction; a motor configured to rotate the polygon mirror; an optical scanning system configured to focus the beam deflected by the polygon mirror on an imaging plane, the optical scanning system including a first scanning lens made of resin; a housing retaining the semiconductor laser, the coupling lens, the polygon mirror, the motor, and the optical scanning system, the housing including a base on one side thereof in an axial direction, the axial direction being a direction of a rotation axis of the polygon mirror; a cover covering the other side of the housing in the axial direction; and a partition enclosing a space where the polygon mirror and the motor are located between the base and the cover, the partition having an opening, through which the deflected beam passes, wherein the first scanning lens closes the opening, the first scanning lens having an optical surface located closest to the polygon mirror among a plurality of optical surfaces included in the optical scanning system, and wherein shifting amounts of a focus position of the beam with respect to a reference imaging plane in the main scanning direction are in relations ΔA<0 and ΔA<ΔB<ΔC, where ΔA mm is a shifting amount in a case where the semiconductor laser, the coupling lens, and the optical scanning system are at a normal ambient temperature, ΔB mm is a shifting amount in a case where the semiconductor laser, the coupling lens, and the optical scanning system are at an upper-limit ambient temperature, and ΔC mm is a shifting amount in a case where the semiconductor laser and the coupling lens are at the normal ambient temperature and the first scanning lens is at a first temperature, the first temperature being higher than the normal ambient temperature.
2 . The optical scanning apparatus according to claim 1 , wherein the shifting amounts are in relations ΔA<ΔD<ΔC, where ΔD mm is a shifting amount in a case where the semiconductor laser, the coupling lens, and the optical scanning system are at a lower-limit ambient temperature.
3 . The optical scanning apparatus according to claim 1 , wherein the optical scanning system includes a second scanning lens located closer to the imaging plane than the first scanning lens, and the first scanning lens has optical power in the main scanning direction greater than optical power in the main scanning direction of the second scanning lens.
4 . The optical scanning apparatus according to claim 1 , wherein the partition is a wall extending along the axial direction, the partition being in contact or connection with the base on one end thereof on the one side in the axial direction and in contact or connection with the cover on the other end thereof on the other side in the axial direction.
5 . The optical scanning apparatus according to claim 4 , wherein the partition is formed integrally with the housing.
6 . An image forming apparatus configured to form an image on a recording sheet, comprising: a photosensitive member configured to form an electrostatic latent image thereon; a developing device configured to supply a developer to the electrostatic latent image to form a developed image on the photosensitive member; a transfer device configured to transfer the developed image onto the recording sheet; and an optical scanning apparatus, comprising: a semiconductor laser; a coupling lens made of resin, the coupling lens having a diffractive optical element on at least one side thereof, the coupling lens being configured to convert light emitted from the semiconductor laser into a beam; a polygon mirror configured to deflect the beam into a main scanning direction; a motor configured to rotate the polygon mirror; an optical scanning system configured to focus the beam deflected by the polygon mirror on the photosensitive member, the optical scanning system including a first scanning lens made of resin; a housing retaining the semiconductor laser, the coupling lens, the polygon mirror, the motor, and the optical scanning system, the housing including a base on one side thereof in an axial direction, the axial direction being a direction of a rotation axis of the polygon mirror; a cover covering the other side of the housing in the axial direction; and a partition enclosing a space where the polygon mirror and the motor are located between the base and the cover, the partition having an opening, through which the deflected beam passes, wherein the first scanning lens closes the opening, the first scanning lens having an optical surface located closest to the polygon mirror among a plurality of optical surfaces included in the optical scanning system, and wherein shifting amounts of a focus position of the beam with respect to a reference imaging plane in the main scanning direction are in relations ΔA<0 and ΔA<ΔB<ΔC, where ΔA mm is a shifting amount in a case where the semiconductor laser, the coupling lens, and the optical scanning system are at a normal ambient temperature, ΔB mm is a shifting amount in a case where the semiconductor laser, the coupling lens, and the optical scanning system are at an upper-limit ambient temperature, and ΔC mm is a shifting amount in a case where the semiconductor laser and the coupling lens are at the normal ambient temperature and the first scanning lens is at a first temperature, the first temperature being higher than the normal ambient temperature.
7 . The image forming apparatus according to claim 6 , wherein the shifting amounts are in relations ΔA<ΔD<ΔC, where ΔD mm is a shifting amount in a case where the semiconductor laser, the coupling lens, and the optical scanning system are at a lower-limit ambient temperature.
8 . The image forming apparatus according to claim 6 , wherein the optical scanning system includes a second scanning lens located closer to the photosensitive member than the first scanning lens, and the first scanning lens has optical power in the main scanning direction greater than optical power in the main scanning direction of the second scanning lens.
9 . The image forming apparatus according to claim 6 , wherein the partition is a wall extending along the axial direction, the partition being in contact or connection with the base on one end thereof on the one side in the axial direction and in contact or connection with the cover on the other end thereof on the other side in the axial direction.
10 . The image forming apparatus according to claim 9 , wherein the partition is formed integrally with the housing.

Description

REFERENCE TO RELATED APPLICATIONS This application claims priority from Japanese Patent Application No. 2023-060338, filed on Apr. 3, 2023. The entire content of the priority application is incorporated herein by reference. BACKGROUND ART In an optical scanning apparatus, a focus position may shift due to changes in ambient temperature, but the shifting amount may be offset by applying a diffractive optical element in an optical system. Such an optical scanning apparatus may have a first imaging optical system, which condenses a beam emitted from a light source, and a second imaging optical system, which scans an imaging plane with the beam deflected by a deflection device, and in either the first imaging optical system or the second imaging optical system, at least one refractive optical element and one diffractive optical element may be provided. By setting a power of the diffractive optical element suitably, the shifting behavior of the focus position on the imaging plane due to changes of oscillation wavelength of the light from the light source and the shifting behavior of the focus position on the imaging plane due to the ambient temperature changes may be corrected. SUMMARY The optical scanning apparatus may have a box-shaped housing, one side of which is open, and the first imaging optical system, a polygon mirror being a deflector, and the second imaging optical system may be supported by the housing. A cover may close the opening of the housing. A motor for driving the polygon mirror may be stowed alongside the polygon mirror in the housing. The motor running active may generate heat to increase the temperature inside the optical scanning apparatus. Meanwhile, if the polygon mirror is tainted with dust or foreign particles contained in the exterior air, reflectance of the polygon mirror may be lowered. As such, deficiencies such as printing errors and inability of obtaining timing to start printing may be caused, and lifetime of the optical scanning apparatus may be shortened. Therefore, in order to prevent the polygon mirror from being tainted, the polygon mirror may be surrounded by partitions so that an area around the polygon mirror may be enclosed securely. In such an arrangement, an opening may be formed in one of the partitions, and a first scanning lens being one of the lenses in an optical scanning system located closest to the polygon mirror may be set in the opening. However, with the first scanning lens located in proximity to the polygon mirror, in other words, in proximity to the motor, a temperature of the first scanning lens may be locally increased by the heat from the motor to be higher than the other parts of the optical system. In the known optical scanning apparatus, such local temperature increase due to the arrangement may not be taken into consideration; therefore, the focus position tends to shift largely. When the focus position is movable by a large amount, a diameter of a beam spot on the imaging plane may vary largely, and an imaging quality may be lowered. The present disclosure relates to an optical scanning apparatus, which may reduce taints on a polygon mirror and may reduce variation of a beam spot diameter on an imaging plane to form a qualified image. According to an aspect of the present disclosure, an optical scanning apparatus an optical scanning apparatus includes a semiconductor laser, a coupling lens, a polygon mirror, a motor, an optical scanning system, a housing, a cover, a partition. The coupling lens is made of resin and has a diffractive optical element on at least one surface thereof. The coupling lens is configured to convert light emitted from the semiconductor laser into a beam. The polygon mirror is configured to deflect the beam into a main scanning direction. The motor is configured to rotate the polygon mirror. The optical scanning system is configured to focus the beam deflected by the polygon mirror on an imaging plane. The optical scanning system includes a first scanning lens made of resin. The housing retains the semiconductor laser, the coupling lens, the polygon mirror, the motor, and the optical scanning system. The housing includes a base on one side thereof in an axial direction, which is a direction of a rotation axis of the polygon mirror. The cover covers the other side of the housing in the axial direction. The partition encloses a space where the polygon mirror and the motor are located between the base and the cover. The partition has an opening, through which the deflected beam passes. The first scanning lens closes the opening. The first scanning lens has an optical surface located closest to the polygon mirror among a plurality of optical surfaces included in the optical scanning system. Shifting amounts of a focus position of the beam with respect to a reference imaging plane in the main scanning direction are in relations ΔA<0 and ΔA<ΔB<ΔC, where ΔA mm is a shifting amount in a case where the semiconductor laser, the coup