JPH09197309A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of an image defect due to stray light with a simple constitution in the case of constituting a spray paint type optical scanner of an over-field type optical system. SOLUTION: A 1st light source optical system and a 1st scanning optical system are arranged on one side of a rotary polygon mirror 14 and a 2nd light source optical system and a 2nd scanning optical system are arranged on the other side of the mirror 14. The elevation angle β1 (an angle formed by a plane B rectangular to the rotation axis A of the mirror 14 and an optical beam L1) of the optical beam L1 made incident from the 1st light source optical system on the reflection face 14A of the mirror 14 from the reflection face 14A is made different from the elevation angle β2 of an optical beam L2 made incident from the 2nd light source optical system on the reflection face 14B of the mirror 14 from the reflection face 14B. Since an optical beam (stray light) reflected by a reflection face different from a reflection face for reflecting light in a recording medium is not applied to another recording medium, the generation of a ghost in the recording medium can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly to an electrophotographic apparatus such as a laser beam printer, a laser copying machine, a laser facsimile machine or the like, in which a light beam is deflected by a light reflection type deflecting device and a recording medium. The present invention relates to an optical scanning device that scans the top.

[0002]

2. Description of the Related Art In recent years, laser printers have attracted attention due to their features such as good image quality and high-speed printout. The non-performance of scanning a recording medium by deflecting a laser beam mounted on the laser printer greatly affects performances such as image quality and print speed of the laser printer.

As shown in FIG. 3, an optical scanning device usually has
Laser diode 100, rotating polygon mirror 102, light source optical system 104 for guiding the laser beam emitted from laser diode 100 to rotating polygon mirror 102, and scanning optics for guiding the laser beam deflected by rotating polygon mirror 102 to recording medium 106 for scanning. It is composed of system 108.

Further, as shown in FIG. 4, in correspondence with the speeding up of color, each of the four color toners (each developing unit 109).
It is included in AD. ) Four recording media 110A
Although there are optical scanning devices corresponding to D to D, the cost of parts is increased because the rotary polygon mirror 112 and the motor 114 for rotating the rotary polygon mirror 112 are required for each recording medium.
There is a technical problem such that it is necessary to accurately match the rotational speed of each rotary polygon mirror 112 in order to match the position of each color.

In order to solve this problem, as shown in FIG. 5, an optical scanning device (referred to as a spray paint type) in which two or more light beams L are incident on one rotary polygon mirror 116 and deflected at the same time. There is. In this type of optical scanning device, it is not necessary to match the rotation speed between the motors,
Only one rotating polygon mirror and one motor are needed (in the example shown in FIG. 5, two rotating polygon mirrors are used, but one may be used).
Therefore, there is no cost for parts.

Further, there are roughly two types depending on the relationship between the rotary polygon mirror and the incident beam. One is a type in which the width D of the incident light beam L is narrower than the width W of one reflecting surface 112A of the rotary polygon mirror 112 and all the incident light beam L is emitted to the scanning lens 120 as shown in FIG. Optical system (hereinafter referred to as an underfield type optical system). On the other hand, as shown in FIG. 7, an overexposure type optical system (hereinafter referred to as an overfield type optical system) in which the width D of the incident light beam L is wider than the width W of one reflecting surface 112A of the rotary polygon mirror 122. ).

[0007]

By the way, when the same scanning lens is used, the overfield type optical system can make the diameter of the rotary polygon mirror smaller than that of the underfield optical system, so that the number of rotations of the motor can be lowered. There are features. However, since a part of the incident beam is cut out and emitted to the scanning lens, there is a problem that the amount of emitted light differs depending on the position on the recording medium, and the image density is partially different. Therefore, in USP 3,558,208, as shown in FIG. 8, before the incident beam is incident on the rotary polygon mirror 112, the transmitted light amount distribution type filter 12 (see FIG. 9) is used in advance.
It has been proposed to shape the light amount distribution of the light beam L by using 6 so that the light amount of the outgoing beam to the scanning lens 128 becomes constant. However, this device has a problem that the number of parts is increased and the cost is increased because a special filter is used.

On the other hand, as shown in FIG. 10, by widening the width of the light beam L incident on the rotary polygon mirror 112 in the light source optical system, the light beam reflected by one reflecting surface 112A of the rotary polygon mirror 130 is changed. It is known that unevenness can be reduced.

However, a spray paint type optical scanning device using the overfield type optical system is constructed as shown in FIG. 11, and the rotary polygon mirror 11 is constituted by the first light source optical system.
When the width of the light beam L1 to the beam No. 2 is widened, a part of the light beam L is different from the reflection surface 112A of the rotary polygon mirror 112, which is different from the reflection surface 112A which is reflected toward the recording medium (not shown). The light beam L1a reflected by the surface 112C (first
The stray light 4) of the light source optical system directly enters the other optical system (second light source optical system) and causes an image defect called a ghost on the other recording medium.

To solve the above problems, it is an object of the present invention to prevent an image defect due to stray light with a simple structure when a spray paint type optical scanning device is constructed using an overfield type optical system.

[0011]

According to a first aspect of the present invention, there is provided an optical scanning device, wherein a plurality of light beams are incident on a single rotating polygon mirror from different directions and are deflected respectively. The incident directions of the light beams of the book to the rotary polygon mirror are different from each other with respect to a plane orthogonal to the rotation axis of the rotary polygon mirror.

In the optical scanning device according to the first aspect, when a spray paint type optical scanning device is constructed by using an overfield type optical system, a plurality of optical beams are directed toward one rotary polygon mirror from different directions. When a light beam is input, a part of each light beam is reflected by a predetermined reflecting surface and is emitted toward a recording medium corresponding to each light beam.

On the other hand, the other part of the light beam incident on the rotating polygon mirror is reflected by another reflecting surface different from the predetermined reflecting surface, but the direction of incidence of the plurality of light beams on the rotating polygon mirror. Are made different from each other with respect to a plane orthogonal to the rotation axis of the rotary polygon mirror, so that another part (stray light) of the light beam reflected by another reflecting surface different from the predetermined reflecting surface is a recording medium. Since the light is emitted in a direction different from that of, it is possible to prevent a ghost on the recording medium due to another part of the light beam.

The invention described in claim 2 is the same as claim 1
In the optical scanning device described in the paragraph 1, the angle difference of at least two of the light beams in the direction orthogonal to the plane is ½ of the spread angle of one light beam in the direction orthogonal to the plane.
And an angle that is 1/2 the spread angle of the other light beam in the direction orthogonal to the plane.

In the optical scanning device according to the second aspect, when the light beam emitted from the reflecting surface has a spread in the sub-scanning direction (direction orthogonal to the main scanning direction), at least two light beams are formed. The angle difference in the direction orthogonal to the plane is defined as the half angle of the divergence angle of one light beam in the direction orthogonal to the plane and the half angle of the divergence angle of the other light beam in the direction orthogonal to the plane. Since the angle is set to be larger than the angle obtained by adding, the ghost on the recording medium due to another part (stray light) can be surely prevented even if the light beam has a spread in the sub-scanning direction.

When three or more light beams are incident on the rotary polygon mirror, each light beam is set so as to satisfy the above requirements with respect to the other light beams.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a main part of an optical scanning device 10 to which the present invention is applied. Optical scanning device 1 of the present embodiment
Reference numeral 0 denotes an optical box 12, and a first light source optical system 16 and a first scanning optical system 18 are arranged on one side of the optical box 12 around a rotary polygon mirror 14 as a rotary light deflecting member. Then, the other second light source optical system 20 and second scanning optical system 22 are arranged on the opposite side with the rotary polygon mirror 14 interposed therebetween.
It is a spray paint type optical scanning device.

The first light source optical system 16 includes a collimator lens 26 and a reflecting mirror 28, and the laser diode 2
The light beam L1 emitted from the collimator lens 2
After being made substantially parallel by 6, the light enters the rotary polygon mirror 14 via the reflecting mirror 28. Further, the light beam L1 is provided between the collimator lens 26 and the reflecting mirror 28 so that the rotary polygon mirror 14
A cylindrical lens 27 for condensing light on the reflection surface of is arranged. A part of the light beam L1 emitted from the laser diode 24 is reflected by one reflecting surface of the rotary polygon mirror 14 and is emitted to the first scanning optical system 18.

The first scanning optical system 18 has a first f
The θ lens 30 and the second fθ lens 32 are provided. A recording medium 34 is arranged in the emission direction of the light beam L1 that passes through the first scanning optical system 18.

Similarly, the second light source optical system 20 also
The collimator lens 38 and the reflecting mirror 40 are provided, and the light beam L2 emitted from the laser diode 36 is made substantially parallel by the collimating lens 38, and then the reflecting mirror 4 is provided.
It is incident on the rotary polygon mirror 14 via 0. Further, between the collimator lens 38 and the reflecting mirror 40, a cylindrical lens 41 for condensing the light beam L2 on the reflecting surface of the rotary polygon mirror 14 is arranged. A part of the light beam L2 is reflected by one reflecting surface of the rotary polygon mirror 14 and is emitted to the second scanning optical system 22.

The second scanning optical system 22 is also the same as the first scanning optical system 18, and the first f.theta. Lens 42 and the second f.theta.
The recording medium 46 is provided with a lens 44, and is arranged in the emission direction of the light beam L2 passing through the second scanning optical system 22.

In this embodiment, the light beam L1 emitted from the laser diode 24 and incident on the rotary polygon mirror 14 and the angle α1 formed by the optical axis S1 of the first scanning optical system 18 are emitted from the laser diode 36. Light beam L2 incident on the rotary polygon mirror 14 and the optical axis S2 of the second scanning optical system 22.
The angle α2 formed by and is the same, but may be different.

At this time, as shown in FIG. 2, the elevation angle of the light beam L1 incident on the reflecting surface 14A of the rotary polygon mirror 14 from the first light source optical system 16 (not shown in FIG. 2) with respect to the reflecting surface 14A ( The angle between the plane B orthogonal to the rotation axis A of the rotary polygon mirror 14 and the light beam L1) β1, and from the second light source optical system 20 (not shown in FIG. 2) to the reflection surface 14B of the rotary polygon mirror 14. The elevation angle β2 of the incident light beam L2 with respect to the reflecting surface 14B is set to be different from the elevation angle β2.
1 and the elevation angle β2, the difference Δγ is the spread angle γ of the light beam L1.
1/2 of 1 and 1 of spread angle γ2 of light beam L2
The angle is set to be larger than the angle obtained by adding the angle // 2 (that is, γ1 / 2 + γ2 / 2 <Δγ).

In this embodiment, the rotation axis A of the rotary polygon mirror 14 is set in the vertical direction, and the first light source optical system 16
(Not shown in FIG. 2) to the reflecting surface 14 of the rotary polygon mirror 14.
The direction of the light beam L1 incident on A is set to the horizontal direction (that is, the elevation angle β1 is 0 °).

Since the elevation angle β1 and the elevation angle β2 are different from each other, the recording medium 34 and the recording medium 46 naturally have different positions in the height direction.

Next, the operation of the present embodiment will be described. In the optical scanning device 10 of the present embodiment, the incident directions of the light beam L1 and the light beam L2 with respect to the rotary polygon mirror 14 are made different from each other with respect to the plane B orthogonal to the rotation axis A of the rotary polygon mirror 14, and γ1 / Since the elevation angle β1 and the elevation angle β2 are set so that the relationship of 2 + γ2 / 2 <Δγ is established, a light beam (stray light) reflected by a reflection surface different from the reflection surface reflected toward the recording medium is radiated to the other recording medium. Can be prevented. As a result, it is possible to prevent the occurrence of a ghost on the recording medium and obtain a high quality image.

In the present embodiment, the rotary axis A of the rotary polygon mirror 14 is set to the vertical direction, but it goes without saying that the direction of the rotary axis A may be other than the vertical direction.

[0029]

As described above, in the optical scanning device according to the first aspect, when the spray paint type optical scanning device is constructed by using the overfield type optical system, the image defect caused by the stray light has a simple structure. It has an excellent effect of being able to prevent. Therefore, it is possible to provide an optical scanning device that can provide high-quality prints at high speed at low cost.

In the optical scanning device according to the second aspect,
Even if the light beam spreads in the sub-scanning direction, it has an excellent effect that image defects due to stray light can be surely prevented.

[Brief description of drawings]

FIG. 1 is a plan view of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a side view of a rotary polygon mirror showing a relationship between light beams which are incident on and reflected by the rotary polygon mirror.

FIG. 3 is a perspective view of a conventional optical scanning device.

FIG. 4 is a side view of a conventional color optical scanning device.

FIG. 5 is a side view of a conventional spray-paint type color optical scanning device.

FIG. 6 is a plan view of an underfield type optical system.

FIG. 7 is a plan view of an overfield type optical system.

FIG. 8 is a plan view of an optical system using a light distribution type filter.

FIG. 9 is a detailed view showing the structure of a light distribution type filter.

FIG. 10 is an explanatory diagram showing an example of a conventional technique.

FIG. 11 is a plan view of a rotary polygon mirror showing a problem of the conventional technique.

[Explanation of symbols]

 10 Optical Scanning Device 14 Rotating Polygonal Mirror A Rotating Axis L1 Light Beam L2 Light Beam

Claims (2)

[Claims] 1. An optical scanning device for causing a plurality of light beams to be incident on one rotating polygon mirror from different directions and deflecting the light beams respectively, wherein an incident direction of the plurality of light beams with respect to the rotating polygon mirror is determined. An optical scanning device, wherein the optical scanning device is different from a plane orthogonal to the rotation axis of the rotary polygon mirror. 2. The angle difference between at least two of the light beams in the direction orthogonal to the plane is 1/2 the spread angle of one of the light beams in the direction orthogonal to the plane, and the other light beam. Of the spread angle in the direction orthogonal to the plane of
2. The optical scanning device according to claim 1, wherein the angle is greater than the angle of / 2.