JPH01302218A - Laser scanner - Google Patents

Abstract

PURPOSE:To remove return light to a laser and to obtain laser light having a variable density irregularity by fitting the window glass plate of the case of a rotary polygon mirror slantingly at a specific angle in a subscanning direction. CONSTITUTION:The window glass 7 for laser light projection of the case of the rotary polygon mirror 2 is fitted slantingly to laser light which is canned by the polygon mirror 2 at theta deg. in the direction (subscanning direction) crossing a laser scanning plane. Consequently, part of the laser light is reflected by the glass plate 7, but the glass slants in the subscanning direction, so the light travels not in the direction of the incident light and never returns to the laser light source. Neither automatic output control over the laser light source nor automatic current control is therefore affected by the return light to prevent the quantity of the laser light from varying, thereby obtaining excellent picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] "Industrial Application Field" The present invention relates to a laser scanning device that performs line scanning of a laser spot imaged on a desired image forming device.

“Conventional technology” In recent years, laser beam printers (hereinafter referred to as LBP)
has attracted much attention due to its advantages such as high image quality and high-speed printout.

The heart of the LBP is the laser scanning device, and the performance of this laser scanning device greatly influences the image quality of the LBP.

FIG. 2 is a perspective view schematically showing the laser beam amplifier and the link, and shows the semiconductor laser element 1 in the laser unit.
Is the light coming out from 0 a collimator lens? ζ The light is converted into parallel light, incident on the rotating polygon mirror λ, becomes a scanning light, and is sent to the imaging optical system 3. Electrophotographic photoreceptor S of image forming apparatus
is imaged.

By the way, since the rotating polygon mirror rotates at high speed, if the surrounding air is not clean, the mirror surface will quickly become dirty, which will have a negative effect on the image. Therefore, the rotating polygon mirror is completely covered and sealed with the case 6 as shown in FIG. Case B is provided with a laser entrance/exit window g to allow the laser to pass through, and a window glass cover is fitted over the laser entrance/exit window g for soundproofing and dustproofing.

Now, in the above-mentioned conventional example, the rotating polygon mirror is placed at the position shown in FIG.
On the other hand, at the position R where the laser beam is incident at right angles within the scanning plane of the laser, the reflected light of the laser beam by the rotating polygon mirror is re-reflected by the window glass 7, and is further reflected by the rotating polygon mirror to form the incident light. The laser light returns along the same optical path in the opposite direction and is imaged on the semiconductor laser element IO.

"Problems to be Solved by the Invention" The returned light focused on the semiconductor laser element lθ has the following effects on the laser.

(1) If the driving method of the semiconductor laser device IO is automatic output control that attempts to keep the light amount constant by detecting the element of the optical sensor disposed inside the semiconductor laser device IO, the return light causes the sensor to Since the amount of light detected is greater than the actual output of the unit, the amount of light is reduced and becomes less than the required amount of light.

(2) If the driving method of the semiconductor laser is automatic current control that tries to keep the current constant, the laser oscillation will be slightly affected by the light focused on the semiconductor laser element/θ, and the laser output will decrease. fluctuate.

Therefore, the amount of laser light changes at the moment when the phenomenon that the laser light is reflected by the window glass 7 and returns onto the semiconductor laser element IO occurs.

Fluctuations in the amount of laser light due to the above phenomenon have a serious effect on images. That is, as mentioned above, the fluctuation in the amount of laser light occurs at the point where the light reflected by the rotating polygon mirror enters the window glass 7i at a right angle in the scanning plane of the laser. arises from

In terms of LBP, the above phenomenon appears in the form of uneven shading near the center of the image. Since the LBP is a printer that features high image quality as described above, such unevenness in density is very noticeable and can be said to be fatal.

Therefore, it was necessary to provide better image quality by suppressing the light returning to the laser and preventing fluctuations in the amount of light from the laser.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems in a laser scanning device and to provide a laser scanning device that does not cause unevenness in density by making it possible to remove light returning to the laser.

[Structure of the invention]

"Means for Solving the Problems" The present invention has a case provided with a rotating polygon mirror inside, and a window provided in the case is sealed with a glass plate for emitting laser light. This is a laser scanning device characterized in that a glass plate is attached at an angle with respect to the laser sub-scanning direction.

"Function" A portion of the laser light is reflected by the glass plate, but since it is tilted with respect to the sub-scanning direction, it is directed in a direction that does not match the incident light and does not return to the laser light source.

Embodiment FIG. 1 is a partial perspective view of a laser scanning device according to an embodiment of the present invention, and the laser scanning device as a whole is the same as that shown in FIG. The window glass 7 has a surface that faces the laser scanning plane (third
It is inclined by θ0 with respect to a plane (hereinafter referred to as the sub-scanning direction) perpendicular to a plane parallel to the plane of the drawing, that is, a plane of movement of the laser beam scanned by a polygon mirror. That is, it is arranged at an angle of 900+θ0 from the laser scanning plane. That is, the light is arranged so that the incident angle with respect to the window glass 7 is θ.

Here, the laser beam L/ incident from the laser unit/ through the window glass 7 is reflected by the mirror surface of the rotating polygon mirror, and when it enters the window glass 7 from the right angle direction on the main scanning plane, it is reflected by the window glass 7? The reflected light L2 reflected at the upper incident point R has an angle θ with respect to the incident light to the incident point R on a plane perpendicular to the main scanning plane containing the incident light L/ incident to the incident point R, It is further reflected by the mirror surface of the rotating polygon mirror and returns to the direction of the angle θ with the incident light L/ from the laser unit to the rotating polygon mirror.

Here, the angle θ is the distance from the window glass 7 to the tip of the collimator lens 9 that converts the laser into parallel light, L,
If the beam diameter of the parallelized laser is D, then l L
tan is an angle that satisfies 2θ1≧D. By doing this, the optical axis of the returned light is shifted by more than the beam diameter of the laser light at the position of the collimator lens, so that it does not return onto the semiconductor laser element 10 of the laser light source.

The same applies when a lens system is arranged between the collimator lens 9 and the rotating polygon mirror 2 in order to prevent dynamic tilting of the rotating polygon mirror 2. In this case, it goes without saying that the amount θ of the inclination of the window glass 7 should be calculated according to the lens system.

When an imaging optical system is installed between the collimator lens and the window glass 7, the angle θ of the window glass 7 is the above-mentioned ILtanx.
At least θ1≧D must be satisfied. Furthermore, if the amount θ of the inclination of the window glass window exceeds 100, there is a strong possibility that flare etc. will occur due to aberrations and adversely affect the image.

For example, the distance from the window glass 7 to a focal length Al1mrs lens (not shown) for preventing dynamic tilting of the rotating polygon mirror is 7S, and the distance between this lens and a collimator lens with a diameter of 1mm is II! ; It was confirmed that in the system where the window glass is tilted by 30 degrees, the reflected light does not return to the collimator lens.

〔Effect of the invention〕

As explained above, the present invention enables the reflected light on the flat surface of the optical component to be reflected by tilting the incident angle by a predetermined angle with respect to the sub-scanning direction of the glass plate disposed at the entrance/exit window of the case covering the rotating polygon mirror. Since it is possible to prevent the laser beam from returning onto the semiconductor laser element, it is possible to provide a laser scanning device with good image quality.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 1 is a schematic perspective view of a laser beam printer, and FIG. 3 is a plan view of a conventional example. /... Laser unit 2... Rotating polygon mirror 6... Case 7... Window glass θ... Tilt is an angle. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. In a laser scanning device that has a case equipped with a rotating polygonal mirror inside and a window provided in the case for emitting laser light is sealed with a glass plate, the glass plate is used for laser sub-scanning. A laser scanning device characterized in that it is installed at an angle with respect to the direction.