JP2000267034A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obain a scanning optical system capable of reducing the variation of the intensity of a laser beam in the whole area of scanning area even when a deflection angle is >=30 deg.. SOLUTION: This optical scanner is provided with a laser light source 1 emitting a linear polarized light beam and a rotary polygon mirror 4 deflecting the laser beam emitted from the light source 1 and using it for scanning at the deflection angle being >=30 deg. and constituted so that the intensity of the laser beam on a prescribed scanning surface can be changed to three values of strong exposure, middle exposure and weak exposure. Besides, it is provided with an adjustment means adjusting the polarizing direction of the laser beam so that three values of the intensity of the laser beam can be held at the almost equal values extending over the whole area of the scanning surface.

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 used for a laser beam printer, a copying device, and the like.

[0002]

2. Description of the Related Art FIG. 2 is a schematic view of a conventional optical scanning device. Light emitted from the light source 1 such as a semiconductor laser is collimated.
The light passes through the lens 2 and is converted into a parallel light beam 7. Thereafter, the light is deflected and scanned by the rotating polygon mirror 4 through the cylindrical lens 3, which is provided for correcting the tilt of the rotating polygon mirror 4, and forms an image on the photosensitive member 6 through the Fθ lens 5. At this time, the light emitting point 1 in the light source 1 such as a semiconductor laser
The spread of the light from 0 is as shown in FIG. In FIG. 3, light beams at both ends in the center and in directions of large and small spread are indicated by arrows. The direction of deflection is indicated by a thick arrow. FIG.
As described above, in the related art, the light spread is large in the X direction (scanning direction) and the light spread is small in the Y direction (scan vertical direction). The deflection direction at this time is the Y direction.

FIG. 4 shows the relationship between the reflectance and the reflection angle of the rotary polygon mirror 4 in this conventional case. The reflectance changes depending on the reflection angle of the rotary polygon mirror 4. For example, if the reflection angle is 15 degrees to 45 degrees, the deflection angle is doubled from 30 degrees to 90 degrees, and becomes ± 30 degrees. At this time, as shown in FIG.
It has been found that the% reflectance differs.

However, in a conventional optical system, this deflection angle is ±
When the angle is 30 degrees or less, the difference in reflectance is 3 as shown in FIG.
%, The laser light source that emits linearly polarized light and the laser beam from the laser light source are deflected and scanned by a rotating polygon mirror, and the light intensity on a predetermined scanning surface of the laser beam is reduced by strong exposure, There was no problem in a scanning optical system that can change to three values of intermediate exposure and weak exposure.

[0005]

As described above, in the conventional optical scanning device, when the deflection angle becomes ± 30 degrees or more, the change in reflectance becomes large accordingly, and the light amount is about 3% or more depending on the scanning position. Can be expected to change.

On the other hand, FIG. 5 shows the relationship between the surface potential on the photoreceptor 6 and the amount of light to be irradiated thereon. V0 in FIG. 5 is a surface potential when the exposure amount is 0. V0 / 2 indicates that the potential is half the value of V0. The exposure amount at this time is defined as E0. Vd is a potential when the exposure amount is four times E0. Here, in order to create the potential of Vd, the exposure amount may be given by 4E0. Even if the exposure amount at this time changes by about 3%, the slope of the graph is very small, so the potential level Vd
Hardly changes.

However, in recent years, there has been a demand for forming a latent image on a photoreceptor using a potential level of V0 / 2 level. In this case, as shown in FIG. 5, since the slope of the V0 / 2 level is about −1, when the exposure amount is changed by 3% or more, the surface potential of the V0 / 2 level is correspondingly 3%. This will change.

If the surface potential at the V0 / 2 level changes by 3% or more, a phenomenon such as a change in print density or a stain on the background may occur in some cases, resulting in deterioration of print quality. Met. The surface potential of the V0 / 2 level has a difference between the maximum and the minimum within 2%, that is, ± 1%
It has been found that the above-mentioned problem of deterioration in print quality can be eliminated by keeping the content within the range.

From the above, it is necessary to provide a scanning optical system capable of giving an exposure amount that is uniform over the entire scanning area, that is, within ± 1% even when the scanning angle is ± 30 degrees or more. I was

On the contrary, the scanning angle at which the exposure amount distribution can be suppressed within ± 1% in the conventional scanning optical system is shown in FIG.
Since the angle is 5 degrees to 37 degrees, the deflection scanning angle is doubled from 30 degrees to 74 degrees, which is a problem because only ± 22 degrees can be scanned.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, there is provided a rotary polygonal surface for deflecting and scanning a laser light source emitting linearly polarized light and a laser beam from the laser light source at a deflection angle of ± 30 degrees or more. A scanning optical system having a mirror and capable of changing the light intensity of the laser beam on a predetermined scanning surface into three values of strong exposure, intermediate exposure and weak exposure, The polarization direction of the laser beam can be adjusted and held so that the three values of the beam intensity are kept substantially equal. For this purpose, a mechanism that makes the light source rotatable about the optical axis may be provided, or a λ / 2 plate may be arranged between the light source and the rotating polygon mirror so as to be adjustable.

A laser light source for emitting linearly polarized light, a rotary polygon mirror for deflecting and scanning a laser beam from the laser light source at a deflection angle of. +-. 30 degrees or more, and a predetermined scanning surface of the laser beam In a scanning optical system capable of changing the above light intensity into three values of strong exposure, intermediate exposure and weak exposure, the three values of the laser beam intensity are maintained at substantially the same values over the entire scanning surface. As described above, the polarization of the laser beam may be circularly polarized, and a λ / 4 plate may be disposed between the light source and the rotary polygon mirror.

[0013]

FIG. 1 is a general view of an embodiment of the present invention. FIG. 1 is the same as the conventional example shown in FIG. 2 except for the optical element 15.

First, light emitted from a light source 1 such as a semiconductor laser passes through a collimator lens 2 and is converted into a parallel light beam 7. The direction of deflection of the light source at this time is the same as the direction of the rotation axis of the rotary polygon mirror 4. Then, an optical element 1 capable of rotating the deflection direction by twice the rotation angle with respect to the optical axis.
5, that is, the [lambda] / 2 plate is arranged at 22.5 degrees around the optical axis. The subsequent light deflection direction is inclined at 45 degrees with respect to the rotation axis of the rotary polygon mirror 4. Thereafter, the light is deflected and scanned by the rotating polygon mirror 4 through the cylindrical lens 3, which is inserted for correcting the tilt of the rotating polygon mirror 4, and is imaged on the photosensitive member 6 through the Fθ lens 5.

On the other hand, as shown in FIG. 6, the rotary polygon mirror 4 has a characteristic in which the relationship between the reflection angle and the reflectance differs depending on the light deflection direction. In this, the deflection direction is set to the rotating polygon mirror 4.
When the angle of inclination is 45 degrees with respect to the rotation axis, even if the reflection angle changes, the change in reflectance falls within ± 1%. The point of the present invention is to utilize this characteristic.

As a first realization method, as described above, the λ / 2 plate is divided into two by the method shown in FIG.
There is a method in which the light is arranged to be rotated by 2.5 degrees and the deflection direction of the light incident on the rotary polygon mirror 4 is rotated by 45 degrees. as a result,
The reflection characteristic of the rotary polygon mirror 4 is shown in FIG.
(Degree rotation), so that even if the reflection angle changes, the change in reflectance falls within ± 1%.

As a second method of realization, FIG.
There is a method shown in FIG. FIG. 7 is an overall view, in which the configuration is the same as that of the prior art. Light emitted from a light source 1 such as a semiconductor laser passes through a collimator lens 2 and is converted into a parallel light beam 7. Thereafter, the light is deflected and scanned by the rotating polygon mirror 4 through the cylindrical lens 3, which is provided for correcting the tilt of the rotating polygon mirror 4, and forms an image on the photosensitive member 6 through the Fθ lens 5. Among them, the light source 1 itself such as a semiconductor laser may be rotated by 45 degrees around the optical axis, and at the same time, the deflection direction may be rotated by 45 degrees. This is shown in FIG.
In FIG. 8, light rays at both ends in the center and in directions of large and small spread are indicated by arrows. The deflection direction is indicated by a thick arrow. Conventionally, light was spread in the X direction (scanning direction) so as to be large and light spread in the Y direction (scan vertical direction). However, the deflection direction can be changed as shown in FIG. Rotated 45 degrees. As a result, the reflection characteristic of the rotary polygon mirror 4 becomes such a characteristic as shown in FIG. 6 (rotation by 45 degrees from the deflection direction Y), so that even if the reflection angle changes, the change in the reflectance falls within ± 1%.

In addition, as a third realization method, there is a method of disposing a λ / 4 plate at the optical element 15 shown in FIG. In this case, the light beam after passing through the optical element 15 can be changed from linearly polarized light to circularly polarized light. In the case of circularly polarized light, the reflection characteristic of the rotary polygon mirror 4 is shown in FIG.
(Rotation by 45 degrees from the above), so that even if the reflection angle changes, the change in the reflectance is within ± 1%.

[0019]

As described above, according to the present invention, the deflection direction of the light beam incident on the rotary polygon mirror 4 is inclined by 45 degrees with respect to the rotation axis of the rotary polygon mirror 4, so that the deflection direction is ± 30 degrees or more. Can provide a scanning optical system in which the difference in reflectance depending on the reflection angle of the rotary polygon mirror 4 is within ± 1%.

Similarly, since the light beam incident on the rotating polygon mirror 4 is circularly polarized, the difference in the reflectance due to the reflection angle of the rotating polygon mirror 4 is different even in a wide-field-of-view scanning optical system of ± 30 degrees or more. However, it is possible to provide a scanning optical system within ± 1%.

Therefore, even if the scanning optical system has a wide angle of view of ± 30 ° or more, the variation in the amount of exposure can be kept within ± 1% over the entire scanning range of the scanning optical system. When it is necessary to keep the light amount of the scanning light within ± 1% over the entire scanning area with a wide-angle scanning optical system of 30 degrees or more, that is, a laser light source that emits linearly polarized light and a laser beam from the laser light source are used. With a rotating polygon mirror that performs deflection scanning with a deflection angle of ± 30 degrees or more,
In a scanning optical system capable of changing the light intensity on a predetermined scanning surface of the laser beam into three values of strong exposure, intermediate exposure, and weak exposure, the laser beam intensity of three values over the entire scanning surface. This is optimal when the values are to be kept substantially equal.

It is apparent that similar effects can be obtained even when four or more levels are formed.

[Brief description of the drawings]

FIG. 1 is a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a conventional example.

FIG. 3 is a diagram supplementarily explaining a conventional example.

FIG. 4 is a graph showing the relationship between the reflectance and the reflection angle of a conventional rotary polygon mirror.

FIG. 5 is a graph showing a relationship between an exposure amount to a photoconductor and a surface potential.

FIG. 6 is a graph showing a relationship between a polarization direction, a reflectance of a rotating polygon mirror, and a reflection angle.

FIG. 7 is an explanatory diagram of a second embodiment of the present invention.

FIG. 8 is a supplementary explanatory diagram of the second embodiment of the present invention.

[Explanation of symbols]

1: a light source such as a semiconductor laser, 2: a collimator lens,
3: Cylindrical lens 4: Rotating polygon mirror, 5: Fθ
Lens, 6: photoreceptor, 7: light beam, 10: light source, 11: expanded light beam, 15: optical element, 20: expanded light beam.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA03 BA04 BA83 2H045 AA01 CB35 CB65 5C072 AA03 BA15 HA02 HA09 HA13 HB02 JA07 XA05

Claims (5)

[Claims] 1. A laser beam source for emitting linearly polarized light, and a rotary polygon mirror for deflecting and scanning a laser beam from the laser beam source at a deflection angle of. +-. 30 degrees or more, on a predetermined scanning surface of the laser beam. The light intensity at high intensity, intermediate exposure and
In an optical scanning device capable of changing to three values of weak exposure, an adjusting means for adjusting the polarization direction of the laser beam so that the three values of the laser beam intensity are kept substantially equal over the entire scanning surface. An optical scanning device, comprising: 2. The optical scanning device according to claim 1, wherein a rotation unit that rotates the light source around the optical axis is provided as the polarization direction adjusting unit. 3. The optical scanning device according to claim 1, wherein a λ / 2 plate is inserted between the light source and the rotating polygon mirror as the polarization direction adjusting means. 4. A laser light source for emitting linearly polarized light, a rotary polygon mirror for deflecting and scanning a laser beam from the laser light source at a deflection angle of. +-. 30 degrees or more, and a predetermined scanning surface of the laser beam In an optical scanning device capable of changing the above light intensity into three values of strong exposure, intermediate exposure and weak exposure, the three values of the laser beam intensity are kept substantially equal over the entire scanning surface. And an adjusting means for changing the polarization of the laser beam to circularly polarized light. 5. The optical scanning device according to claim 4, wherein a λ / 4 plate is disposed between the light source and the rotary polygon mirror as the adjusting means.