JPH0635212Y2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention According to the present invention, a light beam is incident on a rotary polygon mirror frontally through an fθ lens, and after deflecting, the light beam passes through the fθ lens again to scan the surface of the photoconductor. The present invention relates to a double-pass optical scanning device.

Prior Art Examples of a conventional double-pass optical scanning device are shown in FIGS.
It is shown in the figure and explained.

FIG. 4 is a longitudinal sectional view of the main part of the device, and FIG. 5 is a lateral sectional view thereof.

The laser beam generator 1 is a laser beam generator that generates a laser beam modulated according to a recording signal,
An incident laser beam b ₁ is output obliquely downward from the laser beam generator _1, is incident on the fθ lens 2, is further transmitted through the fθ lens 2, and is incident on the window glass 3.

The window glass 3 is a rotary polygon mirror 5 and a polygon mirror drive motor 8
It is a glass window for soundproofing and dustproofing provided in a part of the motor cover 4 that covers the inside of the motor cover 4. The inside of the motor cover 4 is completely sealed and a clean gas 9 of class 100 to 1000 is enclosed.

The incident laser beam b ₁ incident on the window glass 3 is reflected by one reflecting surface of the rotating polygon mirror 5 which passes through the window glass 3 and rotates, and travels obliquely downward as scanning laser beams b ₂ and b ₃ , The light passes through the window glass 3 and the fθ lens 2, reaches the cylindrical mirror 6, is reflected by the cylindrical mirror 6, reaches the drum state optical body 7, and is recorded on the surface of the drum state optical body 7 as an electrostatic latent image. .

Scanning laser beam reflected by the reflecting surface of the rotating polygon mirror 5
b ₂ and b ₃ are scanned in a substantially fan shape, reflected by the cylindrical mirror 6, and scanned on the surface of the drum-shaped photoreceptor 7 on a straight line substantially parallel to the cylindrical axis thereof.

Therefore, the fθ lens 2 compensates for the scanning distortion caused by the rotary polygonal mirror 5 having a constant angular velocity motion so as to obtain a constant linear velocity motion on the surface of the drum-shaped photoconductor 7, and the rotary polygonal facet is also used. Rotating polygonal mirror 5 for incident light accompanying rotation of mirror 5
The cylindrical mirror 6 compensates the scanning pitch unevenness caused by the surface tilt.

In the optical scanning device having the above structure, the collimator lens can be omitted, and the fθ lens 2 and the window glass 3 transmit not only the incident laser beam b ₁ but also the scanning laser beams b ₂ and b ₃ . There is an advantage in that the surface size and hence the outer diameter of the rotary polygon mirror 5 can be reduced to reduce the load on the polygon mirror drive motor 8.

However, since the present device is a double-pass system in which the fθ lens 2 and the window glass 3 transmit the laser beam twice, the light reflected on the surfaces of the fθ lens 2 and the window glass 3 is small. There is a possibility that an unexpected optical signal may be recorded on the surface of the drum-shaped photoconductor 7.

That is, the reflected beam b _{4 on} the outer surface 2a of the fθ lens 2 and the reflected beam b _{5 on} the inner surface 2b of the fθ lens 2 are reflected obliquely downward as indicated by the broken line, and further reflected by the cylindrical mirror 6 to form a drum shape. The surface of the photoconductor 7 is reached.

Since the reflected beams b ₄ and b ₅ are the lights reflected before being scanned by the rotary polygon mirror 5, they always have the same optical path,
A latent image is formed by irradiating the same position in the center of the drum-shaped photoconductor 7 with a slight amount of light, which hinders the sharpness of the image.

In addition to the reflected beams b ₄ and b _{5 described above} , there is also one in which a part of the scanning beams b ₂ and b ₃ once reflected by the rotating polygon mirror 5 is reflected by the outer surface 2a of the fθ lens 2. b ₆ again passes through the window glass 3, is reflected by the reflecting surface of the rotary polygon mirror 5, passes through the window glass 3, fθ lens 2 and is reflected by the cylindrical mirror 6, and then reaches the drum-shaped photosensitive member 7 (broken line). , The unexpected signal may be recorded.

Since this reflected beam b ₆ is the light reflected by the rotating polygon mirror 5 more than once, an unnecessary latent image is formed at the position when it reaches the drum state light body 7 over the entire width direction of the surface of the photoconductor. And the image becomes unclear.

Further, the scanning beams b ₂ , b reflected by the reflecting surface of the rotary polygon mirror 5
A part of ₃ may also be reflected by the inner surface 2b of the fθ lens 2 and the reflected beam b ₇ may be repeatedly reflected inside the device to reach the drum-shaped photoconductor 7, which causes a problem of such a secondary obstacle.

In order to reduce the above problems, an expensive antireflection coating such as a multilayer film may be applied to the surface of the fθ lens 2, but it is extremely expensive.

Means and Actions for Solving Problems The present invention has been made in view of the above points, and an object of the present invention is to block an unnecessary reflected light by arranging a light shielding member at an appropriate position to prevent the photosensitive member from being exposed. The point is to provide an inexpensive optical scanning device capable of obtaining a clear image while avoiding reaching the target.

That is, the present invention makes a light beam such as a laser beam incident on an fθ lens at an angle to the optical axis, deflects the emitted light by a rotary polygon mirror, and then passes the light beam again through the fθ lens to correct a surface tilt correction optics such as a cylindrical mirror. In a double-pass optical scanning device that scans and exposes the surface of a photoconductor through a system, the fθ is provided at a required position between the reflecting surface of the rotary polygon mirror and the surface tilt correction optical system so as not to interfere with incident light and scanning light. It is an optical scanning device in which one or a plurality of light blocking members for blocking the reflected light from the lens are arranged.

By disposing the light shielding member at a required position for shielding the reflected light from the fθ lens, the light partially reflected on the inner and outer surfaces of the fθ lens is shielded so as not to reach the photoconductor, and an unnecessary latent image is formed on the photoconductor. Can be avoided.

Embodiment An embodiment according to the present invention shown in FIGS. 1 to 3 will be described below.

This embodiment has substantially the same structure as the optical scanning device of the conventional example shown in FIGS. 4 and 5, so that the same reference numerals are used for commonly used members.

In this embodiment, the light shielding plates 20 and 21 are provided on both sides of the rotary polygonal mirror 5 and the cylindrical mirror 6 with the fθ lens 2 interposed therebetween.
Are arranged.

The surfaces of both the light shielding plates 20 and 21 are black chromated.

Shielding plate 20 is positioned to intercept the reflected beam b ₅ in the reflected beam b ₄ and the inner surface 2b of the outer surface 2a of the fθ lens 2 of the outer surface 2a incident laser In the side beams b ₁ from and a lower fθ lens 2 It is located in.

Therefore, the light shielding plate 20 shields the reflected beams b ₄ and b ₅ without obstructing the incident laser beam b ₁ and can prevent the reflected beams from reaching the cylindrical mirror 6 and the drum-shaped photoreceptor 7.

Moreover, since the surface of the shading plate 20 is subjected to the black chromate treatment, the reflected beams b ₄ and b ₅ are substantially absorbed by the surface of the shading plate 20 and show an extremely low reflectance, so that it is not necessary to consider the subsequent secondary obstacles. Absent.

Since the reflected beams b ₄ and b ₅ are fixed light beams that do not move, they are applied to the light shielding plate 20 as points.

Therefore, the light shield plate 20 itself needs only to shield the reflected beams b ₄ and b ₅ , so that it has a small area.

The one light shield plate 21 is on the inner surface 2b side of the fθ lens 2 and below the scanning laser beams b ₂ and b ₃ and at the fθ lens 2
It is arranged at a position to intercept the reflected beam b ₇ in the reflected beam b ₆ and an inner surface 2b in the outer surface 2a.

The reflected beams b ₆ and b ₇ move to the left and right because the scanning beams b ₂ and b ₃ are part of the reflected light.

Therefore, the light blocking plate 21 is long in the left-right direction and has a certain width in the vertical direction for blocking the moving reflected beams b ₆ and b ₇ .

That is, FIG. 3 shows III-III in FIGS. 1 and 2.
As shown in the figure, the loci of the incident laser beam b ₁ , the scanning laser beams b ₂ and b ₃ , and the reflected beams b ₆ and b ₇ and the light shield plate are shown.
The positional relationship with 21 is shown.

The incident laser beam b ₁ is indicated by a dot above the center of the light shield plate 21, and the scanning laser beams b ₂ and b ₃ scan from the left to the right above the upper edge of the light shield plate 21 by a distance χ.

The reflected beam b ₆ reflected by the outer surface 2a of the fθ lens 2 is irradiated to the upper half of the surface of the light shielding plate 21, and its locus first appears once as a light beam heading leftward on the left side, and then on the upper and lower sides thereof. Turn to face right, and make another U-turn upward on the right side to end one scan.

This is because the outer surface 2a of the fθ lens 2 has a curvature,
All of these loci fit within the surface of the shading plate 21.

Further, the reflected beam reflected by the inner surface 2b of the fθ lens 2
b ₇ is irradiated on the lower half of the light shielding plate 21 and shows a substantially linear locus from left to right, which is the inner surface of the fθ lens 2.
Since 2b is a plane, the entire locus is included in the surface of the light shielding plate 21.

As described above, the light blocking plate 21 completely blocks only the reflected beams b ₆ and b ₇ without disturbing the incident laser beam b ₁ and the scanning laser beams b ₂ and b ₃ , and the reflected beam reaches the drum-shaped photoconductor 7. It can be avoided.

The surface of the shading plate 21 is also subjected to black chromate treatment, so that the reflectance on the surface of the shading plate 21 is extremely low and there is no risk of secondary damage.

The distance χ between the loci of the scanning laser beams b ₂ and b ₃ and the upper edge of the light shielding plate 21 is χ> 4ω when the beam diameter of the scanning beam (position of 1 / e ² energy) is 2ω. By satisfying the condition, proper exposure is possible without deteriorating the energy of the scanning light to be exposed on the main body drum state light body 7.

However, if χ> 4ω is satisfied, a part of the reflected beam b ₇ may protrude from the light shielding plate 21 and reach the drum state light body 7. However, since the energy of the reflected beam is very small, the reflected beam b ₇ is almost unclear to the print quality. It has no effect.

Further, the light shielding plate 21 may block the reflected light reflected by the window glass 3 although it is small.

As described above, in the present embodiment, since the light shielding plates 20 and 21 almost block the light reflected on the surface of the fθ lens 2,
Even if the remaining slightly leaked light reaches the drum state light body 7, since the energy is very small, it is not easy to form a latent image.

Therefore, an inexpensive antireflection coating can be applied to the surface of the fθ lens 2, or the coating can be omitted, and the cost can be reduced.

In addition to the present embodiment, it is conceivable to shield the reflected light from the window glass 3 by providing a light shielding plate at an appropriate position that does not interfere with the incident laser beam b ₁ and the scanning laser beams b ₂ and b ₃ .

As the antireflection treatment applied to the surface of the light shielding plate, a method such as black sulfuric acid anodic oxidation in addition to the above black chromate treatment can be considered.

EFFECTS OF THE INVENTION The present invention can provide a clear image by arranging the light shielding member at an appropriate position so as to shield unnecessary anti-light shielding so as not to reach the photoconductor.

Further, it is not necessary to apply an expensive antireflection coating to the fθ lens or the like, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an optical scanning device according to an embodiment of the present invention, FIG. 2 is a horizontal sectional view of the optical scanning device, and FIG.
FIG. 3 is a view in the direction of arrow III-III, FIG. 4 is a vertical sectional view of a conventional optical scanning device, and FIG. 5 is a transverse sectional view of the same optical scanning device. DESCRIPTION OF SYMBOLS 1 ... Laser beam generator, 2 ... fθ lens, 3 ... Window glass, 4 ... Motor cover, 5 ... Rotating polygon mirror, 6 ... Cylindrical mirror, 7 ... Drum state optical body, 8 ... Polyhedral drive motor, 9 ... Gas , 20, 21 ... Shading plate, b ₁ ... Incident laser beam, b ₂ , ₃ ... Scanning laser beam, b ₄ ~
₇ … Reflected beam.

Claims (2)

[Scope of utility model registration request] 1. A light beam is made incident on an f.theta. Lens at an angle with respect to the optical axis, emitted light is deflected by a rotary polygon mirror, and then passed through the f.theta. In a double-pass optical scanning device that scans and exposes the light, the reflected light from the fθ lens is shielded at a required position between the reflecting surface of the rotary polygon mirror and the surface tilt correction optical system so as not to interfere with incident light and scanning light. An optical scanning device characterized in that one or a plurality of light blocking members are arranged. 2. The optical scanning device according to claim 1, wherein one or both surfaces of the light shielding member are subjected to antireflection treatment.