Laser scanning optical system and image forming apparatus

• US 7,755,809 B2
• Filed: 11/27/2006
• Issued: 07/13/2010
• Est. Priority Date: 12/26/2005
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Ohno, Takayuki, Ohkubo, Kenzo, Ono, Yasuhiro, Fujita, Hirokazu, Wada, Takasumi
• Primary Examiner(s): Worku; Negussie
• Application Number:
  US11/563,220
• Publication Number:
  US 20070146848A1
• Time in Patent Office: 1,324 Days
• Field of Search: 358/474, 358/501, 358/484, 358/1.9, 358/494, 358/481, 359/204.1, 359/212.2, 359/216.1, 359/196.1, 347/152, 347/249, 347/233, 347/232, 347/235, 347/250, 347/241, 399/301, 399/328, 425/174.4, 235/462.27
• US Class Current: 358/474
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0052 the light source comprising a laser diode coupling into light guides using intermediate optical elements G02B6/4204; semiconductor lasers having optical devices external to the laser cavity H01S5/005
• CPC Class Codes: G02B 26/125 Details of the optical system between the polygonal mirror and the image plane G02B26/123, G02B26/127 take precedence; F-Theta lenses G02B13/0005
• CPC Class Codes: G02B 27/0911 Anamorphotic systems

Abstract

A laser scanning optical system converts a plurality of beams emitted from the laser diode (LD) into parallel light using a collimator lens, shapes the parallel light using an aperture, and executes exposure of a plurality of lines simultaneously on a photoreceptor drum. To cause a necessary emitting point interval d determined uniquely from the magnification of the optical system to coincide with an emitting point interval of the LD used, the LD is rotated by an angle θ against the main optical axis plane thereof. In this case, a converting device that converts the aspect ratio of a profile of the light beam emitted from the LD is provided. A conversion characteristic of the converting device is adjusted such that the characteristic is matched with a condition within a predetermined region following a characteristic of the optical system.

Claims

1. A laser scanning optical system having a semiconductor laser, a collimator lens that converts a plurality of light beams emitted from the semiconductor laser into parallel light, and an aperture that defines a diameter of a spot of the light beam on an image carrier, and the system scanning the light beams emitted from the collimator lens and exposing simultaneously a plurality of lines on the image carrier, wherein

the laser scanning optical system has a converting device that converts an aspect ratio of a profile of the light beam exited from the semiconductor laser, wherein

the converting device converts the plurality of light beams, and wherein

when it is assumed that a main scanning direction is a beam scanning direction in the laser scanning optical system and a sub-scanning direction is a direction perpendicular to the main scanning direction,

$\begin{array}{c}\mathrm{Am}<\end{array}$

1 ( cos 2 ⁢

θ

′

m ⁢

⊥

2 + sin 2 ⁢

θ

′

m ⁢



2 ) [ Equation ⁢

⁢

1 ] As <

1 ( sin 2 ⁢

θ

′

m ⁢

⊥

2 + cos 2 ⁢

θ

′

m ⁢



2 ) [ Equation ⁢

⁢

2 ] L = ⁢



×

β

×

fB fA ×

cos ⁢

⁢

θ

′

[ Equation ⁢

⁢

3 ] m ⊥

= 2 ×

fA ×

tan ⁡

( ⊥

α

⊥

2 ) , and [ Equation ⁢

⁢

4 ] m ⁢



= 2 ×

fA ×

tan ( 

⁢

α



2 ) [ Equation ⁢

⁢

5 ]

hold, where

Am is a width of the aperture in the main scanning direction;

As is a width of the aperture in the sub-scanning direction;

m⊥

is a diameter of an elliptic light beam in a long axis direction;

m∥

is a diameter of the elliptic light beam in a short axis direction;

fA is a focal length of the collimator lens;

fB is a focal length of a back focus lens;

α

⊥

is a divergence angle in a direction perpendicular to lining of semiconductor laser emitting points;

α

∥

is a divergence angle in a direction parallel to the lining of the semiconductor laser emitting points;

β

is a disposition interval of the semiconductor laser emitting points;

θ

′

is a rotation angle formed by the lining direction of the semiconductor laser emitting points and a main scanning plane;

Δ

⊥

is a conversion coefficient of the converting device corresponding to the direction perpendicular to the lining of the semiconductor laser emitting points;

Δ

∥

is a conversion coefficient of the converting device corresponding to the direction parallel to the lining of the semiconductor laser emitting points; and

L is a line pitch of an exposing light beam in the sub-scanning direction.

2. The laser scanning optical system of claim 1, wherein

the collimator lens functions as the converting device by having an anamorphic shape, converts the aspect ratio of the profile of the light beam emitted from the semiconductor laser, and converts the light beam into parallel light.

3. The laser scanning optical system of claim 2, wherein

the collimator lens is adjusted to be at an inclination angle equal to an inclination angle θ

of the semiconductor laser to adjust the pitch in the sub-scanning direction on the image carrier.

4. An image forming apparatus comprising:

the laser scanning optical system of claim 3; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.

5. An image forming apparatus comprising:

the laser scanning optical system of claim 2; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.

6. The laser scanning optical system of claim 1, wherein

the converting device is provided on an optical path between the collimator lens and the semiconductor laser.

7. The laser scanning optical system of claim 6, wherein

the converting device is adjusted to be at an inclination angle equal to an inclination angle of the semiconductor laser to adjust the pitch in the sub-scanning direction on the image carrier.

8. An image forming apparatus comprising:

the laser scanning optical system of claim 7; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.

9. An image forming apparatus comprising:

the laser scanning optical system of claim 6; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.

10. The laser scanning optical system of claim 1, wherein

the converting device is provided on an optical path between the collimator lens and the aperture.

11. The laser scanning optical system of claim 10, wherein

the converting device is adjusted to be at an inclination angle equal to an inclination angle of the semiconductor laser to adjust the pitch in the sub-scanning direction on the image carrier.

12. An image forming apparatus comprising:

the laser scanning optical system of claim 11; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.

13. An image forming apparatus comprising:

the laser scanning optical system of claim 10; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.

14. The laser scanning optical system of claim 1, wherein

the plurality of light beams are emitted light beams by one semiconductor laser having a plurality of emitting points or by a plurality of semiconductor lasers each having one emitting point.

15. An image forming apparatus comprising:

the laser scanning optical system of claim 14; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.

16. An image forming apparatus comprising:

the laser scanning optical system of claim 1; and

a photoreceptor, wherein

the laser scanning optical system forms a latent image on the photoreceptor, the latent image is visualized, and, thereby, image forming is executed.