JPS63239416A - Laser beam scanning optical system - Google Patents

Abstract

PURPOSE:To preclude fluctuations due to air convection by covering the optical path between a laser beam source and a laser beam image formation surface with a cover. CONSTITUTION:The optical path where laser beam 2 emitted by the semiconductor laser 1 passes through a collimator lens 3 and reaches a rotary polygon mirror 4 is covered with the cover 7 that no air permeates, and both ends are sealed hermetically with transparent glass plates 7a and 7b. The front end is arranged nearby the laser 1 and the rear end is arranged nearby the polygon mirror 4. The polygon mirror 4 is rotated to scan the laser beam on an image formation surface 6, so the optical path spreads to the end. The optical path and an ftheta lens 5 are covered with a fan-shaped cover 8. The front end is close to the polygon mirror 4 and glass 8a is provided; and the rear end is close to the image formation surface and glass 8b is provided. There is no heat source in the cover and no convection is generated in the cover, so the laser beam is accurately scanned on the image formation surface to obtain an image of high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image output device such as a laser printer, and particularly to a laser scanning "optical system" that performs highly accurate scanning.

[Conventional technology]

Laser printers are known as devices that output high-quality images at high speed. In this laser printer, a laser beam is deflected by a laser scanning optical system using an optical scanner such as a rotating polygon mirror, and a latent image is created on the photoconductor by scanning the photoconductor with the deflected laser beam. Form. After this latent image is developed, it is transferred onto paper to obtain an output image.

FIG. 2 shows a schematic explanatory diagram of a conventional laser scanning optical system.

In the figure, 1 is a semiconductor laser. semiconductor laser l
The laser beam 2 from the laser beam 2 is made into parallel light by the collimating lens 3. The laser beam 2 from the collimating lens 3 is
The laser beam 2 is irradiated onto a rotating polygon mirror scanner 4, and is deflected according to the rotation of the rotating polygon mirror scanner 4.

The laser beam 2 from the rotating polygon mirror scanner 4 passes through the fθ lens 5
The image is formed on the imaging surface 6 via a rotating polygon mirror scanner 40.
The imaging plane 6 is scanned in accordance with the rotation.

This imaging surface 6 is, for example, the surface of a drum-shaped photoreceptor having a rotation axis along the scanning direction of the laser beam 2, and the scanning of the laser beam 2 in the rotation axis direction by the rotating polygon mirror scanner 4, that is, the main A two-dimensional image is formed on the imaging plane 6 by scanning and sub-scanning by rotation of the drum.

[Problem that the invention seeks to solve]

In the conventional laser scanning optical system, the above-mentioned optical system is housed in a housing, but heat is generated from the drive motor (not shown) included in the semiconductor laser 19 rotating polygon mirror scanner 4, etc. Temperature differences occur within the housing. Therefore, air convection occurs in the optical path from the semiconductor laser 1 to the imaging surface 6, causing fluctuations in the laser light 2. For example, in FIG. 2, if the fluctuation occurs in the laser beam 2a, the irradiation position on the imaging plane 6 will be displaced from the original irradiation position 20 to the irradiation position 20a, resulting in a shift in the scanning position. . Furthermore, since the laser beam 2 is deviated from the original optical path and enters the fθ lens 5, there is a drawback that the imaging performance of the fθ lens 5 is degraded and the image quality is degraded.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, prevent air convection in the optical path, eliminate fluctuations in laser light, and perform scanning with laser light with high accuracy.

[Means and operations for solving the problem] In order to achieve the above object, the laser scanning optical system of the present invention has an optical path between a light source and an imaging plane on which the laser light from the light source is focused. It is characterized by having a surrounding cover.

According to the present invention, since the air within the cover is separated from other parts, air convection within the device will not affect the optical path of the laser beam. That is, there is no air convection within the cover, and the laser light does not fluctuate.

Further, when the cover is provided without including the light source, no heat source is present within the cover, so no convection occurs within the cover.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings. Note that the same parts as in the conventional example are given the same reference numerals.

FIG. 1 is a plan view schematically showing an embodiment of the present invention.

In the figure, A indicates the laser scanning optical system as a whole. In this laser scanning optical system A, a laser beam 2 emitted from a semiconductor laser 1 is made parallel by a collimating lens 3, and is deflected by a rotating polygon mirror scanner 4.
Further, the fθ lens 5 scans while forming an image on the imaging plane 6.

Note that this laser scanning optical system A is similar to the same laser scanning optical system A.
It is assumed that the device is housed in a casing (not shown) of the device to which it is applied.

In this embodiment, in order to prevent fluctuations in the laser beam 2, most of the entire optical path is covered by the covers 7 and 8, with the semiconductor laser 1 and the rotating polygon mirror scanner 4, which are heat sources, removed. This prevents convection from occurring in the surrounding optical path.

That is, in the optical path where the laser beam 2 emitted from the semiconductor laser 1 passes through the collimating lens 3 and reaches the rotating polygon mirror scanner 4, the top, bottom, left and right surfaces of the optical path are covered with non-ventilated covers 7, A transparent cover glass 7a is provided at both ends of the cover 7.

7b is arranged in an airtight manner. The cover 7 is provided so that its front end is close to the semiconductor laser 1 and its rear end is close to the rotating polygon mirror scanner 4. The cover glasses 7a and 7b are made of a material and shaped so as not to affect the straight transmission of the laser beam 2 in the optical path.

In the optical path from the rotating polygon mirror scanner 4 to the image forming surface 6, the laser beam 2 is deflected by the rotating polygon mirror scanner 4, but the laser beam 2 is deflected by rotating the rotating polygon mirror scanner 4 in the direction of the arrow. Since the laser beam 2 scans the image plane 6 in the order of 2b, 2C, and 2d, the optical path of the laser beam 2 is expanded to the end. Therefore, a fan-shaped cover 8 is provided in a portion of this optical path so as to surround this expanded optical path.

The front end of the cover 8 is disposed close to the rotating polygon mirror scanner 4, and a cover glass 8a is provided at this front end. Then, the top, bottom, left and right surfaces of the optical path are covered with a cover 8 so as to surround the fθ lens 5 and the expanded optical path,
The rear end of the cover 8 is extended to a position close to the imaging plane 6, and a cover glass 8b is provided at this rear end.

As mentioned above, in this embodiment, most of the optical path is surrounded by the cover 7.8, so that air convection within the device does not affect the optical path of the laser beam through the cover 7.8. It disappears. Therefore, the laser beam 2 does not fluctuate due to air convection within the device. In addition, since the cover 7.8 is provided with the heat source laser beam 2 and rotating polygon mirror scanner 4 located outside the cover 7.8, there is no heat source inside the cover and convection occurs within the cover. It will no longer occur.

In the above embodiment, the cover 7.8 is made airtight by the cover glasses 7a, 7b, 8a, and 8b, but it is possible to separate the air near the optical path of the laser beam from the air in the area where convection exists. It doesn't have to be completely airtight, as long as it is. For example, cover glasses 7a, 7b,
The optical path may be surrounded only by the cover 7.8 without providing the cover 7.8a and llb, and it has been confirmed that even in this case, it is sufficient to prevent air convection.

As for the light source, a semiconductor laser is preferable from the viewpoint that direct modulation is possible and the device can be made smaller, but the light source is not limited to this, and a gas laser such as a He-Ne laser may also be used. However, in this case, if it is necessary to modulate the laser beam, it is necessary to provide an external modulator between the light source and the collimating lens.

The above-described laser scanning optical system can be applied to devices that require laser beam scanning, such as laser printers, and in this case, the scanning on the photoreceptor surface is performed accurately, resulting in high-quality output without disturbance. An image is obtained.

〔Effect of the invention〕

As described above, according to the present invention, since the optical path of the laser beam is surrounded by a cover, no convection occurs in the air in the optical path, and fluctuation of the laser beam can be prevented. therefore,
Scanning of the imaging plane of the laser beam, such as the photoreceptor surface, becomes accurate, and a high-quality image can be obtained.

[Brief explanation of drawings]

FIG. 1 is a plan view schematically showing an embodiment of the present invention, and FIG. 2 is a plan view schematically showing a conventional laser scanning optical system. Semiconductor laser 2, 2a: Laser beam 3: Collimating lens 4: Rotating polygon mirror scanner 5: fθ lens
6: Imaging surface 7.8: Cover 7a, 7b, 8a, 8b: Copper glass^: Laser scanning optical system Patent applicant Fuji Xerox Co., Ltd. Agent Masu Kobori (and 2 others) Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A laser scanning optical system characterized by being provided with a cover that surrounds an optical path between a light source and an imaging plane on which laser light from the light source forms an image. 2. The laser scanning optical system according to claim 1, wherein the cover is provided without including the light source.