JP2001235697A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-performance optical scanner at a low cost by compensating the optical scanner focus change caused by the profile irregularity of a plastic optical device, and the internal distortion. SOLUTION: Since a first cylindrical lens 4 having negative power is provided in a lens holder 5, an emitted flux turns into an elliptical light flux long to a subscanning direction, but the long axis of the ellipse is made coincident with the subscanning direction by rotating the lens holder 5. In this way, after completing the optical positioning, an adhesive is injected into the engagement part of the lens holder 5 and a laser holder 2, and both are integrated, furthermore, an integrated light source unit 50 is set to a main scanning optical device casing 100 by a screw. A luminous flux from the light source unit 50 is converged only in the subscanning direction by a second cylindrical lens 6 attached next at a scanning optical device casing and a focal line is formed near a deflector reflection plane. The light is made incident to the second optical system by the deflector reflection plane and is image formed on a photoreceptor.

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 an image forming apparatus such as a laser printer and a laser facsimile.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view of an example of an optical scanning device used for an image forming apparatus such as a laser printer or a laser facsimile. The parallel laser light emitted from the light source unit 105 is condensed into a linear light flux near the reflecting surface of the rotating polygon mirror 107 by the cylinder lens 106 having a power convex in the direction perpendicular to the paper surface.
7 is reflected and deflected by rotating in the direction of arrow A. The reflected and deflected light beam is then imaged as a light spot on the image plane by the lens groups 108 and 109 constituting the scanning optical system, and is scanned linearly. As a result, a latent image is formed on the photosensitive drum. The direction in which the light spot is scanned by the optical scanning device is called a main scanning direction, and the direction orthogonal to the plane of the drawing is called a sub-scanning direction. In such an optical scanning device, the light source unit 105, the cylinder lens 106,
Generally, the rotary polygon mirror 107 and the scanning lens systems 108 and 109 are mounted on the optical scanning device housing 100 and positioned.

FIG. 6 is a sectional view of an optical system from a light source unit 105 to a cylindrical lens 106 along an optical path L. The light source unit 105 includes the semiconductor laser 101
And a laser holder 102, a collimator lens 103, and a lens holder 104 that holds the collimator lens. A laser beam emitted from this light source unit is emitted at a desired divergence angle and in a desired direction.
After the positional relationship between the semiconductor laser and the collimator lens is adjusted, it is mounted on the optical scanning device housing 100. As described above, the light beam emitted from the light source unit is strongly converged in the sub-scanning direction by the cylinder lens 106, and forms a focal line near the deflector reflection surface. At this time, the cylinder lens 106 mainly moves in the sub-scanning direction due to an error in the radius of the cylinder lens itself in the sub-scanning direction, a manufacturing error in the scanning lens system provided between the deflector and the image plane, and a focus shift in the sub-scanning direction caused by an assembly error. Is arranged in the optical scanning device housing so as to be adjustable in the front-back direction along the optical axis in order to compensate for

In such an optical scanning device, in recent years, an optical element, particularly a second optical system disposed between the deflector and the image plane,
That is, the use of plastic for the scanning optical system is increasing. This is because plastic molding can form a toric lens or an aspherical lens on glass at low cost.

FIG. 7 is a partial perspective view of an optical scanning device using a plastic lens also for a first optical system between a light source and a deflector, which is disclosed in Japanese Patent Application Laid-Open No. 09-184997. Specifically, in order to compensate for the sub-scanning focus movement due to the temperature of the plastic lens of the second optical system, a member formed integrally with the plastic concave cylinder lens 16 and the glass convex cylinder lens 15 is used as the aforementioned cylinder lens. ing.

[0006]

However, in the prior art, the surface accuracy of a plastic member provided in the first optical system, such as a plastic optical element used in a temperature compensation system, and the internal distortion due to molding, etc., are reduced by the scanning system. There is a problem that a new focus movement is caused as a whole.

In order to increase the precision of the plastic member, the number of cavitations is reduced in order to suppress variations in temperature and pressure in the mold, and the molding tact is lengthened in order to reduce the occurrence of distortion during cooling. Action is required,
Both result in increased component costs.

[0008] With respect to the focus change in the sub-scanning direction due to poor accuracy, the cylindrical lens having power in the sub-scanning direction in the first optical system can be moved in the optical axis direction and adjusted together with the manufacturing error of the second optical system. However, this cannot be adjusted for the focus change in the main scanning direction.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a low-cost, high-performance optical scanning device that corrects a change in focus of an optical scanning device caused by surface accuracy and internal distortion of a plastic optical element.

[0010]

SUMMARY OF THE INVENTION The present invention for solving the above-mentioned problems is based on the fact that illumination light generated from a light source is made substantially parallel by a collimator lens, and then at least one plastic optical member and an anamorphic lens are formed. An optical scanning device that irradiates a rotating polygonal mirror through the imaging device and forms an image of the reflected light on a photosensitive member by an imaging lens system, wherein the collimator lens is integrated with at least one of the plastic optical members, and the anamorphic lens is And independently adjustable.

That is, in the present invention, first, the focus shift in the main scanning direction is adjusted by the light source unit. And
Defocus in the sub-scanning direction of the entire scanning device is adjusted by an independently adjustable cylindrical lens. When the plastic optical member has anamorphic characteristics, the rotation angle about the optical axis is adjusted by rotating the lens holding means together with the collimator lens.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a sectional view of a first optical system from a light source unit to a deflector of an optical scanning device according to the present invention. 1 is a semiconductor laser element, 2 is a laser holder for holding the semiconductor laser element, 3 is a collimator lens, 4 is a first cylindrical lens which is a plastic optical element, and has a concave power in the sub-scanning direction. I have. Reference numeral 5 denotes a lens holder for holding the collimator lens 3 and the plastic cylindrical lens 4. Accordingly, the light source unit 50 includes the semiconductor laser 1, the collimator lens 3, the first cylindrical lens 4, and the lens holder 5.

The light source units 50 are individually adjusted so that different units have the same predetermined imaging performance. By moving the lens holder 5 in the optical axis direction, the semiconductor laser device 1, the collimator lens 3, and the
The distance from the first cylinder lens 4 is adjusted to adjust the divergence angle of the emitted light beam.

Reference numeral 6 denotes a second cylindrical lens which is an anamorphic optical element and has a convex power in the sub-scanning direction. The material of the second lens 6 is different from that of the first cylindrical lens 4, and is, for example, glass. Reference numeral 100 denotes an optical scanning device housing.

FIG. 2 is an optical path diagram of an optical system including the semiconductor laser 1, the collimator lens 3, and the plastic cylindrical lens 4. By moving the lens holder 5 in the direction of arrow A, the emitted light is adjusted in the diverging direction as indicated by Lb. By moving the lens holder 5 in the direction of arrow B, the emitted light is changed to La.
Is adjusted in the convergence direction. Since the divergence angle in the sub-scanning direction can be adjusted by the second cylinder lens 6,
Only the main scanning direction needs to be considered as the divergence angle of the light source unit emission light.

The exit angle of the exit light beam is also the same as the lens holder 5.
Is adjusted by moving in a direction perpendicular to the optical axis.

Since the lens holder 5 has the first cylindrical lens 4 having negative power, the emitted light beam becomes an elliptical light beam long in the sub-scanning direction. The rotation angle of the circumference is adjusted so that the major axis of the ellipse coincides with the sub-scanning direction. After the optical alignment is completed in this manner, an adhesive is injected into the mating portion of the lens holder 5 and the laser holder 2 to integrate them, and further, the integrated light source unit 5
0 is screwed to the main scanning optical device housing 100.

The light beam from the light source unit is then converged only in the sub-scanning direction by the second cylinder lens 6 attached to the scanning optical device housing, forming a focal line near the deflector reflection surface and deflector. The light enters the second optical system and is imaged on the photoconductor by the reflection surface.

The second optical system is an anamorphic optical system having different optical characteristics and focal lengths in the main scanning and sub-scanning directions. More specifically, in the main scanning direction, the second optical system transmits substantially parallel light beams from the light source unit. An image is formed on the photoconductor, and in the sub-scanning direction, it functions to re-image a light beam diverging from a focal line near the deflection surface on the photoconductor. In the sub-scanning direction, in order to converge incident divergent light, the second optical system has a stronger power than that in the main scanning direction. This has a greater effect on the focus movement in the sub-scanning direction than on the direction.

The second cylinder lens 6 is used to correct the focus movement by the second optical system and the focal line position movement due to a radial error of the cylinder lens itself in the sub-scanning direction.
Is adjusted along the optical axis, and then the scanning optical device housing 100
Fixed to

The optical scanning device is mounted on an image forming apparatus,
In the moving state, the temperature of each part of the optical scanning device fluctuates due to environmental temperature, heat generated by the drive motor of the deflector of the optical scanning device, temperature rise of the main body, and the like. In particular, a plastic member has a refractive index change about 10 times that of a glass member due to temperature, and a focal point variation due to temperature changes the imaging state of a spot on a photoconductor. However, even under such temperature changes,
In the first embodiment, since the first cylindrical lens 4 made of plastic having a negative power in the sub-scanning direction and the second cylindrical lens 6 made of glass having a convex power in the sub-scanning direction are provided. Even if the refractive index of the plastic lens changes with the temperature change, the change in focal length cancels out and the whole system works to correct the focus movement, so that good imaging performance is always obtained regardless of the temperature.

Further, the internal distortion and the surface precision error of the plastic optical element used in the first optical system are corrected in both the main and sub directions by adjusting the light source unit 50 and the cylinder 6 as described above.

[Embodiment 2] FIG. 3 shows a plastic convex diffractive optical element 40 having a positive power in the sub-scanning direction instead of the plastic concave cylindrical lens 4.
It is sectional drawing of an optical system. In the first embodiment, the temperature compensation system uses the change in the refractive index of the plastic material due to the temperature rise. However, in the second embodiment, the wavelength change of the semiconductor laser due to the temperature rise and the change in the diffraction angle of the diffraction grating due to the temperature change. Is used.

FIG. 4 is a perspective view of the diffraction grating 40. The lattice shape is a straight line in the main scanning direction and has a convex power only in the sub-scanning direction.

This is because the first embodiment utilizes the change in the refractive index of the plastic optical element for temperature compensation,
In the second embodiment, a change in wavelength of the semiconductor laser due to an increase in temperature and a change in diffraction angle accompanying the change are used.

As the temperature rises, the wavelength of the semiconductor laser shifts to the longer wavelength side, but the diffraction angle decreases accordingly. That is, in a diffraction grating having a convex power, the focal length is increased by increasing the temperature, and the effect of reducing the sub-scanning focal length of the second optical system due to a change in refractive index due to temperature is corrected. [Embodiment 3] In the embodiment, a neutral density filter is incorporated in a light source unit as a plastic optical element.

In recent years, it has become possible to set the intensity of light emitted from the light source unit to be lower than that of the related art, together with the improvement in the sensitivity of the photosensitive member. However, when the semiconductor laser emits light at a low output in order to reduce the intensity, sufficient laser oscillation does not occur, and the spontaneous emission light having a broad wavelength increases, thereby deteriorating the imaging performance of the scanning device and the laser drive current. Light emission response deteriorates. In order to solve these problems, it is desirable that the semiconductor laser emits light at the highest possible intensity within the rating, and a neutral density filter is arranged in the optical path so that the exposure amount on the photoconductor is appropriate. Therefore,
In the third embodiment, the neutral density filter is incorporated in the light source unit as a plastic optical element, and is adjusted integrally with the collimator. As a result, the area of the neutral density filter can be minimized, and the surface accuracy can be reduced.

[0029]

According to the present invention described above, it is possible to easily correct the focus change of the optical scanning device caused by the surface accuracy and internal distortion of the plastic optical element. Therefore, it is not necessary to use a plastic optical component finished with high precision, and an inexpensive high-performance optical scanning device can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first optical system of an optical scanning device according to a first embodiment.

FIG. 2 is an optical path diagram of a first optical system in FIG. 1;

FIG. 3 is a cross-sectional view of a first optical system according to a second embodiment using a plastic diffraction grating.

FIG. 4 is a perspective view of a plastic diffraction grating.

FIG. 5 is a conceptual diagram of a conventional optical scanning device.

FIG. 6 is a sectional view of a first optical system of a conventional optical scanning device.

FIG. 7 is a perspective view of a cylindrical lens used for temperature compensation of a first optical system of a conventional optical scanning device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Laser holder 3 Collimator lens 4 Plastic cylindrical lens 5 Lens holder 40 Plastic diffraction grating 50 Light source unit 100 Optical scanning device housing 110 Photosensitive drum

Claims (6)

[Claims] An illumination light generated from a light source passes through a collimator lens, a plastic optical element, and an anamorph hook optical element to irradiate a rotating polygon mirror, and the reflected light is image-scanned on a photosensitive member by a scanning lens. An optical scanning device, wherein the plastic optical element is held so as to be adjustable integrally with the collimator lens. 2. The optical scanning device according to claim 1, wherein the plastic optical element that can be adjusted integrally with the collimator lens is an anamorphic optical element. 3. The optical scanning device according to claim 2, wherein the plastic optical element that can be adjusted integrally with the collimator lens is an anamorphic lens having a negative power in the sub-scanning direction. 4. The optical scanning device according to claim 2, wherein the plastic optical element that can be adjusted integrally with the collimator lens has a diffraction grating surface having a positive power in the sub-scanning direction. 5. The optical scanning device according to claim 1, wherein the plastic optical element that can be adjusted integrally with the collimator lens is a light reduction unit. 6. The optical scanning device according to claim 1, further comprising an anamorphic lens having power in sub-scanning, which can be adjusted independently of the collimator lens.