JPH0980338A - Scanning optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the scanning speed of scanning light or the curvature and tilt of a scanning line with a variable prism. SOLUTION: The scanning light L1 of a rotary polygon mirror 12 is imaged on a photoreceptor on a rotary drum 13 through an image formation optical system 14. Between the image formation optical system 14 and rotary drum 13, the variable prism 15 constituted so that a couple of glass plates 15a are connected to each other with a bellows 15b and liquid is charged into the sealed space 15c is provided to correct the scanning speed of the scanning light L1 or the curvature or tile of the scanning line by periodically swinging one glass plate 15a and to correct defocusing by varying the isolation distance between both the glass plates 15a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device used in an image forming apparatus such as a laser beam printer or a laser facsimile.

[0002]

2. Description of the Related Art FIG. 7 illustrates a general scanning optical device used in an image forming apparatus such as a laser beam printer or a laser facsimile, which comprises a light source 50 for generating a laser beam and a laser beam generated by the laser source. A collimator lens 50a for collimating light and a cylindrical lens 5 for linearly condensing the collimated laser light on the reflecting surface of the rotary polygon mirror 52.
1 and has an imaging optical system 54 for imaging on the photosensitive member of the reflected light i.e. the rotary drum 53 the scanning light L ₀ of the rotary polygon mirror 52, the scanning light L ₀ for imaging on the photosensitive body rotation An electrostatic latent image is formed by main scanning in the Y-axis direction by rotation of the polygon mirror 52 and sub-scanning in the Z-axis direction by rotation of the rotary drum 53. This electrostatic latent image is visualized by a known electrophotographic process and printed on paper.

The image forming optical system 54 is provided with a spherical lens 54a and a trellis lens 54b, which makes the scanning speed of the scanning light L ₀ imaged on the rotating drum 53 uniform and corrects the distortion of the point image. It has a so-called fθ function. Also,
The rotary polygon mirror 52 and the photoconductor on the rotary drum 53 are arranged so as to have a conjugate relationship with the imaging optical system 54 in the sub-scanning direction (Z-axis direction). This is a rotary polygon mirror 52
This is to prevent the displacement of the scanning light L _{0 in} the Z-axis direction from occurring due to the inclination (face tilt) of the rotation axis of the so-called so-called inclination or bending of the scanning line.

The rotating polygon mirror 52 and the imaging optical system 54 are mounted on the bottom wall of an optical box (not shown), and the light source 5 is used.
0 is unitized with the collimator lens 50a and is fixed to the side wall of the optical box.

[0005]

However, according to the above-mentioned prior art, as described above, an assembly error in assembling the rotary polygon mirror or the imaging optical system into the optical box, the rotary polygon mirror, the spherical lens, and the toric lens. Due to errors in manufacturing such as so-called single component errors, etc., it is not possible to arrange the rotary polygon mirror and the rotary drum in an accurate conjugate relationship with the imaging optical system, and Inclination or bending of the scanning line occurs, or the scanning speed of the scanning light is made uniform f
Problems such as insufficient θ function occur.

Further, when the spherical lens or toric lens of the image forming optical system thermally expands due to a change in environmental temperature or heat generation of the driving portion of the rotary polygon mirror, a remarkable defocus occurs due to the change in the refractive index. It may occur. To avoid this, air is used to accelerate the heat dissipation of the imaging optical system and the drive part of the rotary polygon mirror, and to design an optical system with a large depth of focus, but cooling with air is responsive. It is difficult to obtain satisfactory results in terms of
Further, an optical system having a large depth of focus is unsuitable for reducing the spot diameter of a point image, and cannot be adopted in a recent image forming apparatus with higher definition.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and is capable of easily correcting the scanning speed of the scanning light imaged on the photoconductor and the inclination or bending of the scanning line. It is an object of the present invention to provide a scanning optical device which has high performance and is inexpensive.

[0008]

In order to achieve the above object, a scanning optical device of the present invention comprises a rotating polygon mirror, an image forming optical system for forming an image of the scanning light of the rotating polygon mirror on a photoreceptor, and A variable prism disposed in the optical path of the scanning light, the variable prism having a pair of transparent plates facing each other along the optical path of the scanning light, and an angle adjusting means for changing an included angle between the pair of transparent plates. It is characterized by having.

A fluid is hermetically sealed between the pair of transparent plates, and a distance adjusting means for changing the distance between the transparent plates may be provided.

It is preferable that the angle adjusting means is configured to correct the scanning speed of the scanning light by periodically changing the included angle of both transparent plates in the main scanning surface of the scanning light.

The angle adjusting means may be configured to correct the bending or inclination of the scanning line of the scanning light by periodically changing the included angle of both transparent plates in the sub-scanning surface of the scanning light. Good.

[0012]

The scanning speed and the scanning line of the scanning light are changed by periodically changing the included angle of both transparent plates of the variable prism provided in the optical path of the scanning light of the rotating polygon mirror in accordance with the scanning timing of the scanning light. It is possible to correct the bend or inclination of the.

As described above, the variable prism can easily correct the troubles such as the inclination and bending of the scanning line due to the surface tilt of the rotary polygonal mirror or the unevenness of the scanning speed due to the lack of the fθ function of the imaging optical system. Therefore, even if the rotary polygon mirror or the optical components that form the imaging optical system have some component-to-component errors or assembly errors, it is possible to avoid deterioration of image quality and the like, and to achieve high performance. An inexpensive scanning optical device can be realized.

If the fluid is sealed between the pair of transparent plates and the distance adjusting means for changing the distance between the two transparent plates is provided, the ambient temperature changes and the driving portion of the rotary polygon mirror generates heat. For example, when the refractive index of the image forming optical system changes and a focus shift occurs, the distance between the two transparent plates is changed to adjust the refractive index of the variable prism to eliminate the focus shift. be able to. If it is configured to automatically detect the temperature change or the like and change the separation distance of the transparent plate, it is possible to prevent the image quality or the like from being deteriorated due to the change of the environmental temperature or the heat generation of the driving unit of the rotary polygon mirror. A scanning optical device with stable performance can be realized.

[0015]

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

FIG. 1 is an explanatory view for explaining a scanning optical device according to an embodiment, which is a light source 1 for generating a laser beam.
0, a collimator lens 10a for collimating the generated laser light, a cylindrical lens 11 for linearly focusing the collimated laser light on the reflecting surface of the rotary polygon mirror 12,
An image forming optical system 14 for forming an image of the reflected light of the rotary polygon mirror 12, that is, the scanning light L ₁ on the photosensitive member on the rotating drum 13,
The scanning light L ₁ imaged on the photoconductor forms an electrostatic latent image by main scanning in the Y-axis direction by rotation of the rotary polygon mirror 12 and sub-scanning in the Z-axis direction by rotation of the rotary drum 13. This electrostatic latent image is visualized by a known electrophotographic process and printed on paper.

The image forming optical system 14 is provided with a spherical lens 14a and a trillic lens 14b, which makes the scanning speed of the scanning light L ₁ imaged on the rotating drum 13 uniform and corrects the distortion of the point image. It has a so-called fθ function. Also,
The rotary polygon mirror 12 and the photoconductor on the rotary drum 13 are arranged so as to be in a conjugate relationship with the imaging optical system 14 in the sub-scanning (Z-axis direction). This is for avoiding the displacement of the scanning light L _{1 in} the Z-axis direction, that is, the occurrence of tilting or bending of the scanning line due to tilting (surface tilt) of the rotary polygon mirror 12.

The rotary polygon mirror 12 and the imaging optical system 14 are assembled on the bottom wall of an optical box (not shown), and the light source 1 is used.
0 is unitized with the collimator lens 10a and fixed to the side wall of the optical box.

In such a scanning optical device, an assembly process for assembling the rotary polygon mirror 12 and the imaging optical system 14 into an optical box, and a manufacturing process for the rotary polygon mirror 12, the spherical lens 14a, the toric lens 14b, etc. Errors Due to errors such as so-called single component errors, the image forming position on the photoconductor is displaced, causing various troubles. That is, if the conjugate relationship between the rotary polygon mirror 12 and the rotary drum 13 is inaccurate, so-called tilting or bending of the scanning line that causes the imaging position to shift in the Z-axis direction due to surface tilt occurs, and the imaging optical system 14 a scanning speed fθ function impaired is the imaging position of the scanning light L ₁ becomes uneven scanning speed shifted in the Y-axis direction is generated magnification error becomes nonuniform. Further, when the temperature of the spherical lens 14a or the toric lens 14b changes due to the change of the environmental temperature or the heat generation of the driving part of the rotary polygon mirror 12, the refractive index changes due to the thermal expansion, and the imaging position of the scanning light L ₁ is changed. Occurs in the X-axis direction, so-called focus shift occurs.

Therefore, a variable prism 15 which can freely change the image forming position of the scanning light L _{1 in} the X-axis direction, the Y-axis direction and the Z-axis direction is provided between the image forming optical system 14 and the rotary drum 13. The variable prism 15 has a pair of transparent glass plates 15a, which are opposed to each other, and a bellows 15b arranged between them, and a sealed space 15c is formed by both the glass plates 15a and the bellows 15b. Is filled with a liquid that is a high refractive index fluid.

A pair of plate glasses 15a of the variable prism 15
Is parallel to the YZ plane and the included angle between them is zero, the scanning light L ₁ goes straight without being bent by the variable prism 15. However, as shown by the broken line in FIG. When the angle between the two glass plates 15a in the XZ plane, which is the sub-scanning plane, changes by rotating around the Y axis, the optical path of the scanning light L ₁ is refracted in the Z axis direction by the variable prism 15, and the scanning light L ₁ is deflected by this amount. As a result, the image forming position of L ₁ is displaced in the Z-axis direction.

At this time, the following relationship is established between the inclination angle δθ ₁ of one plate glass 15a of the variable prism 15 and the refraction angle δθ of the scanning light L ₁ by the variable prism 15.

Δθ / δθ ₁ = n (1) where n is the refractive index of the liquid filled in the closed space 15c of the variable prism 15. For example, the refractive index n of the liquid is 1.4. If it is ˜1.5, the optical path of the scanning light L ₁ is inclined by about half of the inclination angle δθ ₁ of the plate glass 15a.

If the distance between the variable prism 15 and the photoconductor on the rotary drum 13 is D, the inclination angle δθ ₁ of the plate glass 15a of the variable prism 15 and the deviation of the image forming position on the rotary drum 13 in the Z-axis direction Δ. The following relationships are established between Z.

Δθ ₁ = tan ⁻¹ (ΔZ / D) / (n−1) (2) For example, as shown in FIG. 3, a scan that is originally straight in the Y-axis direction. When the line A is curved as shown by the curve B due to the surface tilt of the rotary polygon mirror 12 and is displaced by ΔZ at the position indicated by Y ₁ , the image forming position is −Δ from the formula (2). Z
₁ only seeking inclination angle .delta..theta ₁ of the glass sheet 15a of variable prism 15 for moving the scanning light L ₁ is scanned light L ₁ The glass pane 15a as .delta..theta ₁ only glass sheet 15a is inclined when it reaches the Y ₁ position An angle adjusting means for swinging in synchronism with the scanning timing is provided. In this way, the bending of the scanning light L _{1 at} the Y ₁ position (positional deviation in the Z-axis direction) can be eliminated, and the original straight scanning line A can be obtained.

Next, as shown in FIG. 4, the variable prism 1
When one plate glass 15a of No. 5 is rotated around the Z axis to change the included angle of both plate glasses 15a in the XY plane which is the main scanning surface, the image forming position on the photoconductor is ΔY in the Y axis direction. As a result, there is a deviation, and the following relationship is established between this and the inclination angle δθ ₂ of the plate glass 15a, as in the equation (2).

Δθ ₂ = tan ⁻¹ (ΔY / D) / (n−1) (3) For example, as shown in FIG. 5, originally, the Y ₁ position should be set at a predetermined timing. When the image forming position which should be in (1) is delayed by ΔY ₁ due to the insufficient fθ function of the image forming optical system 14, the inclination of the plate glass 15a for advancing the image forming position by ΔY ₁ is obtained from the equation (3). seeking angle .delta..theta _2, in the same manner as described above in synchronization with the timing of the scanning of the scanning light L ₁ glass sheet 15
Angle adjusting means for periodically swinging a by δθ ₂ is provided. As a result, the delay of the scanning light L _{1 at} the Y ₁ position can be eliminated and the scanning speed can be made uniform.

Further, as shown in FIG. 6, the variable prism 1
When the amount of the liquid filled in the closed space 15c of No. 5 is changed to change the separation distance between both plate glasses 15a by δd, the image forming position of the rotary drum 13 on the photoconductor moves by ΔX in the X-axis direction.

ΔX = δd · (1−n / n ₀ ) ··· (4) where n ₀ : refractive index of air Therefore, the variable prism 15 is provided with a liquid injection port 15 d to set the ambient temperature. If a pump 15e is provided as a separation distance adjusting means that senses a change in the temperature of the rotary polygon mirror 12 or heat generated in the driving unit of the rotary polygon mirror 12 and automatically increases or decreases the liquid in the closed space 15c to change the separation distance between the two glass plates 15a. By automatically correcting the focus shift of the imaging optical system 14, it is possible to realize a scanning optical device with extremely stable performance.

[0030]

Since the present invention is configured as described above, it has the following effects.

Since the inclination or bending of the scanning line of the scanning light imaged on the photosensitive member or the non-uniformity of the scanning speed can be easily corrected, the cost of assembling the rotating polygon mirror or the imaging optical system as a single component or assembling cost can be increased. It is possible to realize an extremely high-performance scanning optical device. Further, it is possible to automatically eliminate the focus shift caused by the change of the environmental temperature and the heat generation of the driving portion of the rotary polygon mirror, which can greatly contribute to the stabilization of the performance of the scanning optical device.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a scanning optical device according to an embodiment.

FIG. 2 is an explanatory diagram illustrating a case in which the included angle of the variable prism of the apparatus in FIG. 1 is changed in the XZ plane.

FIG. 3 is a graph showing a displacement of an image forming position in the Z-axis direction.

FIG. 4 is an explanatory diagram illustrating a case where the included angle of the variable prism of the apparatus in FIG. 1 is changed in the XY plane.

FIG. 5 is a graph showing a displacement of an image forming position in the Y-axis direction.

6 is an explanatory diagram illustrating a case where the image forming position of the apparatus in FIG. 1 is changed in the X-axis direction.

FIG. 7 is an explanatory diagram illustrating a conventional example.

[Explanation of symbols]

 10 Light source 11 Cylindrical lens 12 Rotating polygonal mirror 13 Rotating drum 14 Imaging optical system 14a Spherical lens 14b Toric lens 15 Variable prism 15a Plate glass 15c Closed space 15e Pump

Claims (4)

[Claims] 1. A rotary polygon mirror, an image forming optical system for forming an image of scanning light of the rotary polygon mirror on a photoconductor, and a variable prism arranged in an optical path of the scanning light. A scanning optical device comprising: a pair of transparent plates facing each other along the optical path of the scanning light; and an angle adjusting means for changing an included angle between the pair of transparent plates. 2. The scanning optical device according to claim 1, wherein a fluid is hermetically sealed between the pair of transparent plates, and a separation distance adjusting means for changing the separation distance between the transparent plates is provided. 3. The angle adjusting means is configured to correct the scanning speed of the scanning light by periodically changing the included angle of both transparent plates in the main scanning surface of the scanning light. The scanning optical device according to claim 1 or 2. 4. The angle adjusting means is configured to correct the bending or inclination of the scanning line of the scanning light by periodically changing the included angle of both transparent plates in the sub-scanning surface of the scanning light. The scanning optical device according to claim 1 or 2, characterized in that: