JP-2026074490-A - Optical scanning apparatus and image forming apparatus having the same

JP2026074490AJP 2026074490 AJP2026074490 AJP 2026074490AJP-2026074490-A

Abstract

[Problem] To provide a compact optical scanning device while employing the UFS method. [Solution] The optical scanning device according to the present invention comprises a deflector that deflects a light beam from a light source to scan the surface to be scanned in the main scanning direction, and a first optical system that guides the light beam deflected by the deflector to the surface to be scanned, wherein in the main scanning cross-section, the width of the light beam immediately before it enters the deflector is smaller than the width of the deflection surface of the deflector, and in the main scanning cross-section, only a portion of the light beam that enters the deflector reaches multiple image heights on the surface to be scanned via the deflection surface, and when the distance between the image height closest to the axial image height on one side of the multiple image heights and the axial image height is Y1 (mm), and the distance between the image height closest to the axial image height on the other side of the multiple image heights and the axial image height is Y2 (mm), -0.005≦(Y2-Y1)/(Y2+Y1)≦0.005 It is characterized by satisfying the following conditions. [Selection Diagram] Figure 1

Inventors

吉田博樹
木村一己
加藤隼人

Assignees

キヤノン株式会社

Dates

Publication Date: 20260507
Application Date: 20241021

Claims (14)

A deflector that deflects the light beam from the light source to scan the surface to be scanned in the main scanning direction, The system comprises a first optical system that guides the light beam deflected by the deflector to the surface to be scanned, In the main scanning section, the width of the light beam immediately before it enters the deflector is smaller than the width of the deflection surface of the deflector. In the main scanning section, at multiple image heights on the scanned surface, only a portion of the light beam incident on the deflector reaches through the deflection surface. When Y1 (mm) is the distance between the image height closest to the on-axis image height on one side of the plurality of image heights and the on-axis image height, and Y2 (mm) is the distance between the image height closest to the on-axis image height on the other side of the plurality of image heights and the on-axis image height, -0.005≦(Y2-Y1)/(Y2+Y1)≦0.005 An optical scanning device characterized by satisfying the following conditions.
When the distance between the first off-axis image height and the on-axis image height on one side is Y3 (mm), and the distance between the second off-axis image height and the on-axis image height on the other side is Y4 (mm), Y3-Y1≦5.00 Y4-Y2≦5.00 The optical scanning apparatus according to claim 1, characterized in that it satisfies the following conditions.
The system includes a second optical system that directs the light beam from the light source onto the deflector, The optical scanning apparatus according to claim 1, characterized in that when projected onto the main scanning cross-section, the center of the light-emitting surface of the light source is not on the optical axis of the second optical system.
The optical scanning apparatus according to claim 3, characterized in that the center of the light-emitting surface is positioned on the opposite side of the scanned surface with respect to a cross-section parallel to the sub-scanning direction that includes the optical axis of the second optical system.
Let Z3 be the distance in the sub-scanning direction between the reaching position at the first off-axis image height on one side of the light beam deflected by the deflection surface and the optical axis of the first optical system, let Z4 be the distance in the sub-scanning direction between the reaching position at the second off-axis image height on the other side of the light beam deflected by the deflection surface and the optical axis of the first optical system, and let Z0 be the distance in the sub-scanning direction between the reaching position that is furthest from the reaching position at one of the first and second off-axis image heights corresponding to the larger of Z3 and Z4, and the optical axis of the first optical system, and when the angle that the normal makes with respect to the main scanning cross-section in a cross-section parallel to the sub-scanning direction that includes the normal of the deflection surface, 0.30≦(Z3+Z4)/{Z0+Max(Z3, Z4)}≦0.82 The optical scanning apparatus according to claim 1, characterized in that it satisfies the following conditions.
The optical scanning apparatus according to claim 1, characterized in that the number of light-emitting points included in the light source is one.
The light source has a plurality of light-emitting points, including a first and a second light-emitting point. In the main scanning cross-section, when the normal to the deflection surface forms a first angle with respect to the optical axis of the first optical system, only a portion of the first luminous beam from the first light-emitting point incident on the deflector is deflected by the deflection surface and reaches the first off-axis image height on one side, while the entirety of the second luminous beam from the second light-emitting point incident on the deflector is deflected by the deflection surface and reaches the first off-axis image height. The optical scanning apparatus according to claim 1, characterized in that, in the main scanning cross-section, when the normal of the deflection surface forms a second angle with respect to the optical axis of the first optical system, the entire first light beam incident on the deflector is deflected by the deflection surface and reaches the second off-axis image height on the other side, while only a portion of the second light beam incident on the deflector is deflected by the deflection surface and reaches the second off-axis image height.
The light source is located on one of the sides, In the main scanning plane, when the normal to the deflection plane is at the first angle, the number of luminous beams that reach the first off-axis image height is n1, where only a portion of the multiple luminous beams from the multiple light-emitting points incident on the deflector are deflected by the deflection plane. In the main scanning plane, when the normal to the deflection plane is at the second angle, the number of luminous beams that reach the second off-axis image height is n2, where only a portion of the multiple luminous beams incident on the deflector are deflected by the deflection plane. 1 ≤ n1 ≤ n2 The optical scanning apparatus according to claim 7, characterized in that it satisfies the following conditions.
The system includes a second optical system that directs the light beam from the light source onto the deflector, When the number of deflection surfaces is N, and the angle between the optical axis of the first optical system and the optical axis of the second optical system in the main scanning cross-section is θ (°), (720/N)/(N-1)+45<θ<(720/N)/(N-1)+60 The optical scanning apparatus according to claim 1, characterized in that it satisfies the following conditions.
The system includes a second optical system that directs the light beam from the light source onto the deflector, When L is the distance on the optical axis of the second optical system between the light-emitting surface of the light source and the on-axial deflection point on the deflection surface, and W is the distance between the first off-axis image height on one side and the second off-axis image height on the other side, 0.30 ≤ L/W ≤ 0.70 The optical scanning apparatus according to claim 1, characterized in that it satisfies the following conditions.
The optical scanning apparatus according to claim 1, characterized in that the deflector is a polyhedron mirror that rotates around a rotation axis.
A deflector that deflects the light beam from the light source to scan the surface to be scanned in the main scanning direction, The system comprises a first optical system that guides the light beam deflected by the deflector to the surface to be scanned, In the main scanning cross-section, the width of the light beam immediately before it enters the deflection surface of the deflector is smaller than the width of the deflection surface. An optical scanning apparatus characterized in that, in the main scanning cross-section, when the normal of the deflection surface forms a predetermined angle with respect to the optical axis of the first optical system, only a portion of the light beam incident on the deflector is deflected by the deflection surface and reaches the surface to be scanned.
An image forming apparatus comprising: an optical scanning apparatus according to any one of claims 1 to 12; a developer for developing an electrostatic latent image formed on the scanned surface by the optical scanning apparatus as a toner image; a transfer unit for transferring the developed toner image to a transfer material; and a fuser for fixing the transferred toner image to the transfer material.
An image forming apparatus comprising an optical scanning device according to any one of claims 1 to 12, and a printer controller that converts a signal output from an external device into image data and inputs it to the optical scanning device.

Description

This invention relates to an optical scanning device, and more particularly to an optical scanning device suitably used in image forming apparatuses such as laser beam printers (LBPs), digital copiers, and multifunction printers. Conventionally, optical scanning devices have been used as exposure devices mounted on image forming equipment such as laser beam printers that use electrophotographic processes. Optical scanning devices can be classified into under-filled scanning (UFS) and over-filled scanning (OFS) types depending on the relationship between the magnitude of the incident light beam entering the deflector and the size of the deflection surface. Specifically, in the UFS method, the width of the incident light beam incident on the deflector within the main scanning plane is smaller than the width of the deflection surface of the deflector, whereas in the OFS method, the width of the incident light beam incident on the deflector within the main scanning plane is larger than the width of the deflection surface of the deflector. Patent Document 1 discloses an optical scanning device employing the UFS method. Japanese Patent Publication No. 2005-92129 A cross-sectional view of the main scanning and a partially sub-scanning of the optical scanning apparatus according to the first embodiment.This figure shows the dependence of the position of the deflection point on the deflection plane of a polygon mirror on the rotation angle.This figure shows the dependence of the incident position of each ray on the rotation angle in a polygon mirror.This figure shows the scan lines formed on the scanned surface when the polygon mirror is malfunctioning in the optical scanning apparatus according to the first embodiment.A cross-sectional view of the main scanning and a partially sub-scanning of the optical scanning apparatus according to the second embodiment.This figure shows the scan lines formed on the scanned surface when the polygon mirror is malfunctioning in the optical scanning apparatus according to the second embodiment.A sub-scanning cross-sectional view of the main parts of a monochrome image forming apparatus and a color image forming apparatus according to an embodiment. The optical scanning apparatus according to this embodiment will be described in detail below with reference to the attached drawings. Note that the drawings shown below may be drawn to a different scale than the actual dimensions in order to facilitate understanding of this embodiment. In the following explanation, the main scanning direction is the direction perpendicular to the rotation axis of the polygon mirror 5 and the optical axis of the imaging optical system 7 (the direction in which the light beam is deflected by the polygon mirror 5), and the sub-scanning direction is the direction parallel to the rotation axis of the polygon mirror 5. Furthermore, the main scanning cross-section is the cross-section parallel to the main scanning direction and the optical axis of the imaging optical system 7 (perpendicular to the sub-scanning direction), and the sub-scanning cross-section is the cross-section parallel to the sub-scanning direction and the optical axis of the imaging optical system 7 (perpendicular to the main scanning direction). This embodiment relates to an optical scanning device, and more particularly to an optical scanning device that records image information by deflecting a light beam emitted from a light source using a polygon mirror as a deflector and scanning it on a surface to be scanned via an imaging optical system. Furthermore, the optical scanning apparatus according to this embodiment is suitably used in image forming apparatuses such as printers, digital copiers, and multifunction printers that have an electrophotographic process. [First Embodiment] Traditionally, when designing a new optical scanning device, reusing existing components as much as possible while still meeting the specifications helps to reduce initial investment and overall product costs. For example, if there is a demand for higher speed or higher image quality compared to conventional methods, it is possible to reduce initial investment by increasing the number of deflection surfaces of the polygon mirror while reusing conventional optical elements. On the other hand, simply increasing the number of deflection surfaces of a polygon mirror could lead to an increase in the size of the polygon mirror, or a shift in the position of the deflection point relative to the incident light beam on the deflection surface, potentially causing field curvature and thus degrading optical performance. Now let's consider the case where a polygon mirror with five deflection faces (hereinafter referred to as a pentagonal polygon) is used instead of a polygon mirror with four deflection faces (hereinafter referred to as a tetrahedral polygon). In such cases, by setting the width of each deflection surface of the pentahedron polygon within the main scanning cro