JP2002090677A - Optical scanner and image-forming apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact optical scanner of simple structure, in which deformations of an image, distortion aberrations are satisfactorily corrected and the eccentricity jitters, the multi-beam jitters, or the like of an optical deflector is decreased, and to provide an image-forming apparatus, using the optical scanner. SOLUTION: The optical scanner is provided with a first optical system, which transforms the state of a light beam emitted from a light source means into another state, a second optical system which introduces the light beam transformed by the first optical system into a deflection element, and a third optical system which focuses the light beam deflected by the deflection element to a plane to be scanned. The values of a single lens which form the third optical system with the radius of curvature near the axis in the main scanning plane, the amount of aspherical amount, and the distance to the plane to be scanned are decided appropriately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning apparatus and an image forming apparatus using the same, and more particularly to deflecting a light beam emitted from a light source means after being light-modulated by a light deflector (deflection element) comprising a rotary polygon mirror or the like. After that, image information is recorded by optically scanning the surface to be scanned through an imaging optical system having fθ characteristics, such as a laser beam printer (LBP) having an electrophotographic process or a digital copying machine. It is suitable for the device.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning device used for a laser beam printer, a digital copying machine, or the like, a light beam which is light-modulated and emitted from a light source means in accordance with an image signal is converted into a light beam comprising a rotating polygon mirror. The light is periodically deflected by a deflector, focused on a photosensitive recording medium (photosensitive drum) surface in the form of a spot by an imaging optical system having fθ characteristics, and the surface is optically scanned to record an image. .

FIG. 12 is a sectional view (main scanning sectional view) of a main portion of a conventional optical scanning device of this type in the main scanning direction.

In FIG. 1, a divergent light beam emitted from a light source means 91 is converted into a substantially parallel light beam by a collimator lens 92, and the light beam (light amount) is restricted by a stop 93, and has a predetermined refractive power only in the sub-scanning direction. The light is incident on the lens 94. Of the parallel light beams that have entered the cylindrical lens 94, they are emitted as they are within the main scanning plane. In the sub-scanning plane, the light deflector 95 is formed by converging and being constituted by a rotating polygon mirror (polygon mirror).
Is formed as a substantially linear image on the deflecting surface (reflection surface) 95a.

The light beam deflected by the deflecting surface 95a of the optical deflector 95 is guided through an imaging optical system (fθ lens) 96 having fθ characteristics onto a photosensitive drum surface 97 as a surface to be scanned. By rotating the optical deflector 95 in the direction of arrow A, the photosensitive drum surface 97 is optically scanned in the direction of arrow B. As a result, the photosensitive drum surface 9 as a recording medium
7 is recorded.

[0006]

In order to record a high-definition image in a conventional optical scanning device, it is necessary to (1) satisfactorily correct the field curvature over the entire surface to be scanned; (2)
It is necessary to have distortion for scanning the scanned surface at a constant speed, and (3) to have a good spot diameter and spot shape on the image surface (scanned surface).

Various optical scanning devices satisfying these optical characteristics have been conventionally proposed.

Various compact and low-cost optical scanning devices having these optical characteristics have also been proposed.
For example, JP-A-8-76011 and JP-A-8-320446 disclose an fθ lens system composed of one lens.

Japanese Unexamined Patent Publication No. Hei 8-76011 discloses that one fθ lens is constituted by a meniscus lens having a convex surface facing the optical deflector, and the convergent light flux from the collimator lens is passed through the optical deflector. An image is formed on the surface to be scanned by the fθ lens.

In general, when the light beam going to the optical deflector is a convergent light beam, eccentric jitter (polygon jitter) of the optical deflector tends to occur. When the light source is a multi-beam light source having a plurality of light-emitting portions, the multi-beam jitter tends to be conspicuous.

Japanese Patent Application Laid-Open No. 8-320446 discloses that both lens surfaces of one fθ lens are formed in a non-arc shape within the main scanning plane, and the amount of non-arc is two degrees of freedom between the scanning position and the image forming point. Is stipulated independently.

However, since the lens surface R2 of the fθ lens on the surface to be scanned has a concave surface facing the optical deflector, the thickness of the fθ lens tends to increase. Therefore, from the viewpoint of processing time and cost reduction during lens molding, it is not considered that the cost has been reduced.

According to the present invention, the fθ lens for forming an image of the light beam deflected by the deflection element on the surface to be scanned is constituted by a single lens, and the paraxial radius of curvature, the amount of aspherical surface, etc. of the fθ lens are set appropriately. The optical scanning device having a compact and simple configuration and an image forming apparatus using the same, which corrects field curvature and distortion, and prevents eccentric jitter of an optical deflector and multi-beam jitter generated by multiple beams. The purpose is to provide.

[0014]

According to a first aspect of the present invention, there is provided an optical scanning device for converting a state of a light beam emitted from a light source unit into another state, and converting the light beam with the first optical system. An optical scanning device comprising: a second optical system that guides the deflected light beam to the deflecting element; and a third optical system that images the light beam deflected by the deflecting element on a surface to be scanned. Is composed of a single lens, and both lens surfaces of the single lens both have an aspheric shape in the main scanning plane, at least one lens surface of which is a toric surface, and a paraxial curvature in the main scanning plane. The radii are R1 and R2 in this order from the deflection element side, the maximum effective diameter in the main scanning plane is Ymax, and the maximum effective diameter Ymax is
S1 is the amount of aspheric surface of the lens surface on the deflection element side from the paraxial lens surface, and S2 is the amount of aspheric surface of the lens surface on the scanned surface side at the maximum effective diameter Ymax.
When the focal length of the single lens in the main scanning plane is ft, and the distance from the single lens to the surface to be scanned is Sk, 0 <R1 <R2 S1 <0 S2 <(R2 ² −Ymax ² ) ^1/2 −R2−0.2 ≦ 1−Sk / ft ≦ 0.2 The condition is satisfied.

According to a second aspect of the present invention, in the first aspect of the present invention, the light source means comprises a multi-beam light source having a plurality of light emitting portions capable of independently modulating light.

According to a third aspect of the present invention, in the first aspect, the shape of the single lens in the main scanning plane is asymmetric with respect to the optical axis of the single lens.

According to a fourth aspect of the present invention, in the first aspect, the axis of symmetry of the single lens in the main scanning direction is tilted and / or shifted with respect to a perpendicular bisector of the surface to be scanned. Features.

A fifth aspect of the present invention is characterized in that, in the first aspect of the present invention, both the lens surfaces of the single lens have their curvatures in the sub-scanning surface continuously changing in the lens effective portion.

According to a sixth aspect of the present invention, in the first aspect of the invention, the lateral magnification of the single lens in the sub-scanning direction is substantially constant in the lens effective portion.

According to a seventh aspect of the present invention, in the first aspect, the first optical system converts the light beam emitted from the light source means into a substantially parallel light beam, a weakly convergent light beam, or a weakly divergent light beam in the main scanning plane. It is characterized by having.

According to an eighth aspect of the present invention, there is provided an image forming apparatus comprising: the optical scanning device according to any one of the first to seventh aspects; a photosensitive member disposed on the surface to be scanned; A developing device for developing the electrostatic latent image formed on the photoreceptor as a toner image by the light flux, a transfer device for transferring the developed toner image to a transfer material, and a transfer device for transferring the transferred toner image to the transfer material. And a fixing device for fixing the toner image to the toner image.

[0022]

FIG. 1 is a sectional view (main scanning sectional view) of a main scanning direction of an optical scanning device according to a first embodiment of the present invention, and FIG. 2 is a diagram showing a third optical system shown in FIG. FIG. 3 is an enlarged explanatory view of the fθ lens of FIG. Here, the main scanning direction refers to the direction in which the light beam is deflected and scanned on the deflection surface of the optical deflector. Further, the main scanning surface refers to a light beam surface formed with time by a light beam deflected by the deflection surface of the optical deflector.

In FIG. 1, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. Reference numeral 2 denotes a condensing lens (collimator lens) as a first optical system, which converts a divergent light beam (light beam) emitted from the light source means 1 into a substantially parallel light beam in the main scanning plane. Reference numeral 3 denotes an aperture stop for adjusting the diameter of a passing light beam.

Reference numeral 4 denotes a cylindrical lens as a second optical system, which is in a sub-scanning direction (a direction perpendicular to the plane of FIG. 1).
And a light beam having passed through the aperture stop 3 is turned into a deflecting surface 5a of an optical deflector 5 described later in the sub-scanning surface.
Is formed as a substantially linear image. Therefore, the light beam incident on the light deflector 5 becomes a line image elongated in the main scanning direction.

Reference numeral 5 denotes an optical deflector composed of, for example, a polygon mirror (rotating polygon mirror) as a deflecting element, which is rotated at a constant speed in a direction indicated by an arrow A in the figure by driving means (not shown) such as a motor.

Reference numeral 6 denotes an fθ lens as a third optical system, which is a single lens having fθ characteristics. lens 6 has a lens surface 6a on the optical deflector 5 side and a lens surface 6b on the surface to be scanned 8 both aspheric in the main scanning plane,
At least one of the lens surfaces is constituted by a toric surface. lens 6 forms a light beam based on the image information deflected by the optical deflector 5 into a spot on a photosensitive drum surface 8 as a surface to be scanned, and the optical deflector 5
Of the deflecting surface is corrected.

The sub-scanning surface (the main scanning surface including the optical axis of the fθ lens 6) of at least one of the lens surfaces 6a and 6b (both lens surfaces in this embodiment) of the two lens surfaces 6a and 6b of the fθ lens 6 in this embodiment. In the effective portion of the lens surface, the curvature is continuously changed from on-axis to off-axis, and the shape of the fθ lens 6 in the main scanning direction is perpendicular to the scanning surface 8. It is configured asymmetrically with respect to the bisector.

In this embodiment, the fθ lens 6 may be manufactured by plastic molding, or may be manufactured by glass molding (glass mold).

Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned.

In this embodiment, the divergent light beam emitted from the semiconductor laser 1 is converted by the condenser lens 2 into a substantially parallel light beam in the main scanning plane, and the light beam (light amount) is restricted by the aperture stop 3 to the cylindrical lens 4. It is incident. The luminous flux incident on the cylindrical lens 4 is emitted as it is in the main scanning plane. Further, in the sub-scanning plane that includes the optical axis and is orthogonal to the main scanning plane, the light converges and forms an almost linear image (a linear image that is long in the main scanning direction) on the deflecting surface 5a of the optical deflector 5. And the optical deflector 5
The light beam deflected by the deflecting surface 5a is guided on the photosensitive drum surface 8 via the fθ lens 6, and the light deflector 5 is rotated in the direction of arrow A to move the light deflector 5 in the direction of arrow B on the photosensitive drum surface 8. Optical scanning. Thus, an image is recorded on the photosensitive drum surface 8 as a recording medium.

Next, a means for correcting distortion and field curvature of the present embodiment will be described.

In this embodiment, the collimator lens 2
Is incident on the fθ lens 6 through the optical deflector 5 from the optical deflector 5 and is substantially parallel in the main scanning plane. Therefore, in order to satisfy the fθ characteristics, the paraxial curvature of the fθ lens 6 in the main scanning plane is required. The radii are R1, R
When 2 is set, the following condition is satisfied: 0 <R1 <R2 ‥‥‥ (1)

That is, the shape of the fθ lens 6 is a meniscus shape protruding toward the optical deflector 5 near the optical axis.
Both a and 6b are aspherical. Since the aspherical shape has the same spot diameter in the sub-scanning direction according to the image height, the maximum effective diameter in the main scanning plane is set to Ymax and the maximum effective diameter Ymax.
The amount of aspherical surface of the lens surface on the side of the optical deflector 5 from the paraxial lens surface at S1 is S1, and the scanned surface 8 at the maximum effective diameter Ymax
Assuming that the aspherical amount of the lens surface on the side from the paraxial lens surface is S2, the following condition is satisfied: S1 <0 ‥‥‥ (2) S2 <(R2 ² −Ymax ² ) ^1/2 -R2 ‥‥‥ (3) Is determined so as to satisfy the following condition.

The maximum effective diameter Ymax in the main scanning plane of the fθ lens 6 is deflected by the optical deflector 5, and the principal ray of the light beam heading toward the scanning start position (or scanning end position) on the surface 8 to be scanned. The distance from the optical axis at a point where the fθ lens 6 intersects the lens surface.

In general, the spot diameter is proportional to the FNo. Therefore, in order to make the spot diameter in the sub-scanning direction due to the image height uniform, the variation of the FNo in the sub-scanning direction due to the image height is suppressed. It is necessary to keep the lateral magnification (sub-scanning magnification) in the direction substantially constant. Therefore, in the present embodiment, the lateral magnification of the fθ lens 6 in the sub-scanning direction is set to be substantially constant in the lens effective portion.

The above conditional expression (1) is a condition for satisfactorily correcting field curvature and distortion. If the conditional expression (1) is not satisfied, it is necessary to correct field curvature and distortion satisfactorily. It's not good because it gets harder.

Conditional expressions (2) and (3) are conditions for making the spot diameter in the sub-scanning direction uniform according to the image height, and any one of the conditional expressions (2) and (3) can be used. If it deviates, it becomes difficult to make the spot diameter uniform in the sub-scanning direction.

In this embodiment, each conditional expression (1),
Fθ so that at least one of (2) and (3) is satisfied.
By setting the lens shape of the lens 6, the uniformity of the spot diameter in the sub-scanning direction is improved while maintaining good curvature of field and distortion.

Next, means for reducing jitter generated by the optical deflector will be described with reference to FIGS. FIG.
5 are explanatory diagrams in the main scanning plane.

Generally, the deflection surface of the optical deflector has a variation in the distance from the rotation center to the deflection surface due to a mounting error with respect to the motor rotation axis, a manufacturing error, or the like. For example, as shown in FIG. 3, even when the light beam is deflected to the same deflection angle, the deflection point changes back and forth depending on the deflection surface used. This causes jitter as shown in FIG. 4 and degrades the image quality. At this time, the jitter amount J represents the deviation amount of the two light beams after being deflected by different deflection surfaces, and the lateral magnification in the main scanning direction (horizontal scanning main magnification).
Is m, J = mh.

The lateral magnification m is as shown in FIG.
Is the focal length in the main scanning plane of ft, the fθ lens 6
When the distance from to the scanned surface 8 is Sk, m = 1−Sk / ft. Therefore, the jitter amount J can be expressed as J = (1−Sk / ft) h.

The jitter is as follows: the main scanning lateral magnification m is -0.2 <m
If <0.2, there is no visual problem.

Therefore, in the present embodiment, the power arrangement of the fθ lens 6 and the collimator lens 2 is appropriately adjusted so as to satisfy the following condition: −0.2 ≦ 1−Sk / ft ≦ 0.2 (4) By setting
A compact scanning optical device in which jitter due to the mounting error of the optical deflector 5 is reduced is obtained.

The above conditional expression (4) is for alleviating the jitter due to the mounting error of the optical deflector 5, and when the value exceeds the upper limit of the conditional expression (4), the jitter becomes visually noticeable. Not so good. If the lower limit value of the conditional expression (4) is exceeded, the distance between the fθ lens 6 and the surface 8 to be scanned becomes long, which makes it difficult to make the whole apparatus compact, which is not good.

In the present embodiment, the light beam incident on the fθ lens 6 is a substantially parallel light beam, that is, the lateral magnification m of the fθ lens 6 in the main scanning direction is m = 1−Sk / ft ≒ 0. No eccentric jitter (polygon jitter) occurs.

In the present embodiment, the lens shape of the fθ lens 6 is represented using the following function. The intersection of the lens surface of the fθ lens 6 and the optical axis is the origin, the optical axis direction is the x axis,
When the axis orthogonal to the optical axis in the main scanning plane is the y-axis, and the axis orthogonal to the optical axis in the sub-scanning plane is the z-axis,

[0047]

(Equation 1)

(Where R is the radius of curvature, K, B ₄ , B ₆ ,
B ₈ and B ₁₀ are represented as aspheric coefficients).

In the sub-scanning direction, as shown in FIG. 1, the scanning start side and the scanning end side with respect to the optical axis, and the sub-scanning surface of at least one of the two lens surfaces 6a and 6b of the fθ lens 6. The curvature in the plane (including the optical axis and perpendicular to the main scanning plane) is continuously changed from on-axis to off-axis in the effective portion of the lens surface. The axis is configured asymmetrically with respect to the perpendicular bisector (normal) of the surface 8 to be scanned,

[0050]

(Equation 2)

Is represented by

In this embodiment, in order to correct the focus in the sub-scanning direction and the uniformity of the magnification of the fθ lens 6 in the sub-scanning direction, both lens surfaces of the fθ lens 6 in the sub-scanning direction are used as described above. Although both 6a and 6b are changed, depending on the lens shape in the main scanning direction, it is possible to correct both aberrations by changing only one surface, which simplifies the lens shape and is effective in manufacturing. It has the feature of.

Table 1 shows the optical arrangement and f in this embodiment.
The aspherical coefficient of the θ lens 6 is shown.

[0054]

[Table 1]

From Table 1, R1 = 67.5 R2 = 1080 S1 = −4.8 S2 = −3.7 (R2 ² −Ymax ² ) ^1/2 −R2 = −0.41 These values Are the above-mentioned conditional expressions (1),
(2) and (3) are satisfied.

FIG. 6 is an aberration diagram showing curvature of field, distortion, and the like in the present embodiment. From the figure, it can be seen that each aberration is corrected to a level at which there is no practical problem.

[Embodiment 2] FIG. 7 shows Embodiment 2 of the present invention.
3 is a cross-sectional view (main scanning cross-sectional view) of a main part in the main scanning direction of FIG. In the figure, the same elements as those shown in FIG. 1 are denoted by the same reference numerals.

This embodiment differs from the first embodiment in that the light beam incident on the fθ lens 16 is a weakly convergent light beam, and that the lens shape of the fθ lens 16 in the main scanning plane is the same as that of the fθ lens 16. That is, the light source means 21 is constituted by a multi-beam light source having a plurality of light emitting points (light emitting portions) which can independently modulate light. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus, similar effects are obtained.

Here, the weakly convergent light beam means that the lateral magnification m in the main scanning direction is defined in a range represented by 0 <m = 1−Sk / ft <0.2.

That is, in the drawing, reference numeral 16 denotes an fθ lens, which has a lens shape in the main scanning plane which is asymmetric with respect to the optical axis. As a result, in the present embodiment, the asymmetric component of the aberration is satisfactorily corrected. Reference numeral 21 denotes light source means, which is composed of a multi-beam light source having a plurality of light emitting points (light emitting portions) that can independently modulate light.

In this embodiment, the asymmetric component of aberration is corrected by forming the lens shape of the fθ lens 16 in the main scanning plane asymmetric with respect to the optical axis. The vertical bisector (normal)
This can also be achieved by shifting or / and tilting the symmetry axis of the fθ lens 16 in the main scanning direction. The correction by shift and / or tilt is characterized in that the lens shape of the fθ lens 16 can be configured symmetrically with respect to the optical axis, so that the lens shape is simplified and is effective in manufacturing.

In this embodiment, the lens shape of the fθ lens 16 is represented by using the following function. Each fθ lens 1
The origin is the intersection of the lens surface of No. 6 with the optical axis, and the optical axis direction is x
Axis, the direction orthogonal to the optical axis in the main scanning plane is the y-axis, the direction orthogonal to the optical axis in the sub-scanning plane is the z-axis, and the lens shape of the fθ lens 16 in the main scanning plane is relative to the optical axis. Since they are asymmetric, the aspherical coefficient on the scanning start side with respect to the optical axis is suffix s, and the aspherical coefficient on the scanning end side is suffix e.

[0063]

(Equation 3)

(Where R is the radius of curvature, K, B ₄ , B ₆ ,
B ₈ and B ₁₀ are represented as aspheric coefficients).

The sub-scanning direction is

[0066]

(Equation 4)

Is expressed as follows.

Table 2 shows the optical arrangement and f in this embodiment.
The aspherical coefficient of the θ lens 16 is shown.

[0069]

[Table 2]

From Table 2, R1 = 59.4 R2 = 212 S1 = -6. O S2 = −5.3 (R2 ² −Ymax ² ) ^1/2 −R2 = −2.0, and these values are determined by the above-described conditional expressions (1) and (2).
(2) and (3) are satisfied.

In the present embodiment, since the lateral magnification m of the fθ lens 16 in the main scanning direction is m = 1−Sk / ft = 0.19, polygon jitter and multi-beam jitter are generated but do not cause a visual problem. Fθ lens 16
Since the lateral magnification in the sub-scanning direction is also corrected to be substantially constant within the effective lens area, the spot diameter is well corrected within the effective lens area, and the pitch interval error of the multi-beam is also well corrected.

In this embodiment, the fθ lens 16
By changing the incident light beam to a weakly convergent light beam, the distance to the surface 8 to be scanned can be shortened, thereby making the entire apparatus more compact. Fθ lens 16
Since the thickness of the lens can be reduced, the cost of the lens can be reduced.

FIG. 8 is an aberration diagram showing curvature of field, distortion, and the like in the present embodiment. From the figure, it can be seen that each aberration is corrected to a level at which there is no practical problem.

[Embodiment 3] FIG. 9 shows Embodiment 3 of the present invention.
3 is a cross-sectional view (main scanning cross-sectional view) of a main part in the main scanning direction of FIG. In the figure, the same elements as those shown in FIG. 7 are denoted by the same reference numerals.

This embodiment differs from the second embodiment in that the light beam incident on the fθ lens 26 is a weakly divergent light beam. Other configurations and optical functions are substantially the same as those of the second embodiment, and thus, similar effects are obtained.

Here, the weakly divergent light beam means that the lateral magnification m in the main scanning direction is defined in a range represented by -0.2 <m = 1-Sk / ft <0.

Table 3 shows the optical arrangement and f in this embodiment.
9 shows the aspheric coefficient of the θ lens 26.

[0078]

[Table 3]

From Table 3, R1 = 62.3 R2 = 1410 S1 = −4.7 S2 = −3.6 (R2 ² −Ymax ² ) ^1/2 −R2 = −0.3 These values are obtained. Are the above-mentioned conditional expressions (1),
(2) and (3) are satisfied.

In the present embodiment, the lateral magnification m of the fθ lens 26 in the main scanning direction is m = 1−Sk / ft = −0.08
Therefore, polygon jitter and multi-beam jitter are generated, but do not cause a visual problem. Fθ lens 2
Since the lateral magnification 6 in the sub-scanning direction is also corrected to be substantially constant within the lens effective area, the spot diameter is corrected well within the lens effective area, and the pitch interval error of the multi-beam is also corrected well.

Further, in the present embodiment, the fθ lens 2
6 is converted into a weakly divergent light beam, so that fθ
While bringing the lens 26 closer to the optical deflector,
The lens diameter can be reduced, and the cost can be reduced.

FIG. 10 is an aberration diagram showing curvature of field, distortion, and the like in the present embodiment. From the figure, it can be seen that each aberration is corrected to a level at which there is no practical problem.

[Image Forming Apparatus] FIG. 11 is a sectional view of a main portion in the sub-scanning direction showing an embodiment of an image forming apparatus (electrophotographic printer) using any one of the optical scanning apparatuses according to the first to third embodiments of the present invention. FIG. In FIG. 11, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by the printer controller 111 in the apparatus. This image data Di
Is input to the optical scanning unit (optical scanning device) 100 according to any one of the first to third embodiments. Then, from the optical scanning unit 100, a light beam (light flux) 103 modulated according to the image data Di is emitted.
03 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

The photosensitive drum 101 serving as an electrostatic latent image carrier (photoconductor) is rotated clockwise by a motor 115. Then, along with this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction orthogonal to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface.
The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with a light beam 103 scanned by the optical scanning unit 100.

As described above, the light beam 103 is
The light is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. This electrostatic latent image is further moved from the irradiation position of the light beam 103 to the photosensitive drum 101.
Is developed as a toner image by a developing device 107 disposed so as to contact the photosensitive drum 101 on the downstream side in the rotation direction of the photosensitive drum 101. As the toner particles used here, for example, those having a sign opposite to the charge charged by the charging roller 102 are used. Then, a portion (image portion) where the toner adheres to the non-exposed portion of the photosensitive drum is formed. That is, in the present embodiment, so-called regular development is performed. In this embodiment, reversal development in which toner adheres to the exposed portion of the photosensitive drum may be performed.

The toner image developed by the developing device 107 is transferred below the photosensitive drum 101 onto a sheet 112 as a material to be transferred by a transfer roller 108 disposed so as to face the photosensitive drum 101. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (right side in FIG. 11), but can be fed manually. At the end of the paper cassette 109, the paper feed roller 1
10 are provided, and the paper 1 in the paper cassette 109 is provided.
12 to the transport path.

The sheet 112 onto which the unfixed toner image has been transferred as described above is further moved behind the photosensitive drum 101 (FIG. 1).
1 is conveyed to the fixing device (left side). The fixing device has a fixing roller 113 having a fixing heater (not shown) therein.
And a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113. The paper 112 scattered from the transfer unit is transferred to the fixing roller 113 and the pressure roller 1.
The unfixed toner image on the paper 112 is fixed by heating while applying pressure at the pressure contact portion 14. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and discharges the fixed paper 112 to the outside of the image forming apparatus.

Although not shown in FIG. 11, the print controller 111 not only converts the explanation data first, but also the motor 115 and other components in the image forming apparatus,
The control of the polygon motor and the like in the optical scanning unit 100 is performed.

[0089]

According to the present invention, as described above, the fθ lens for imaging the light beam deflected by the deflecting element on the surface to be scanned is constituted by a single lens, and the paraxial radius of curvature of the fθ lens and the aspherical surface. By properly setting the amount, etc., it is possible to satisfactorily correct the curvature of field and distortion and to use the multi-beam laser with multiple light emitting points as the light source, as well as the eccentric jitter due to the mounting error of the optical deflector etc. It is possible to reduce the generated multi-beam jitter and the like, and achieve a compact and simple optical scanning device and an image forming apparatus using the same.

[Brief description of the drawings]

FIG. 1 is a main scanning sectional view of a first embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of the fθ lens shown in FIG. 1;

FIG. 3 is an enlarged explanatory view of a part of the optical deflector shown in FIG. 1;

FIG. 4 is an explanatory diagram showing a correlation between a two-beam shift and a jitter amount according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a positional relationship from an optical deflector to a surface to be scanned according to the first embodiment of the present invention.

FIG. 6 is an aberration diagram showing a field curvature and a distortion according to the first embodiment of the present invention.

FIG. 7 is a main scanning cross-sectional view according to a second embodiment of the present invention.

FIG. 8 is an aberration diagram showing a field curvature and a distortion in the second embodiment of the present invention.

FIG. 9 is a main scanning sectional view of Embodiment 3 of the present invention.

FIG. 10 is an aberration diagram showing a field curvature and a distortion according to the third embodiment of the present invention.

FIG. 11 is a cross-sectional view of a main part in a sub-scanning direction showing a configuration example of an image forming apparatus (electrophotographic printer) using the scanning optical device of the present invention.

FIG. 12 is a main scanning sectional view of a conventional optical scanning device.

[Explanation of symbols]

 Reference Signs List 1 light source means (semiconductor laser) 2 first optical system (collimator lens) 3 aperture stop 4 second optical system (cylindrical lens) 5 deflecting means (optical deflector) 6, 16, 26 third optical system ( fθ lens) 8 scanned surface (photosensitive drum surface) 21 light source means (multi-beam semiconductor laser) 100 optical scanning device 101 photosensitive drum 102 charging roller 103 light beam 107 developing device 108 transfer roller 109 paper cassette 110 paper feed roller 111 printer controller 112 Transfer material (paper) 113 Fixing roller 114 Pressure roller 115 Motor 116 Discharge roller 117 External device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 13/00 G02B 13/08 13/08 13/18 13/18 B41J 3/00 D H04N 1/113 H04N 1/04 104A F-term (reference) 2C362 AA09 BA58 BA84 BA86 BB14 2H045 AA01 BA02 BA23 BA32 CA04 CA34 CA55 CA68 2H087 KA19 LA22 PA01 PB01 QA02 QA06 QA12 QA32 RA06 RA08 RA12 UA01 5C072 AA03 HA01 DA06

Claims (8)

[Claims] 1. A first optical system for converting a state of a light beam emitted from a light source means into another state, a second optical system for guiding a light beam converted by the first optical system to a deflection element, A third optical system that forms an image of the light beam deflected by the deflecting element on a surface to be scanned. The third optical system comprises a single lens, and both lenses of the single lens Both surfaces have an aspherical shape in the main scanning plane, at least one lens surface of which is a toric surface, and whose paraxial curvature radii in the main scanning plane are R1, R2, main scanning in order from the deflection element side. The maximum effective diameter in the plane is Ymax,
The aspherical amount of the lens surface on the deflection element side from the paraxial lens surface at the maximum effective diameter Ymax is S1, and the maximum effective diameter Yma
The amount of aspherical surface of the lens surface on the scanned surface side from the paraxial lens surface at x is S2, the focal length of the single lens in the main scanning surface is ft, and the distance from the single lens to the scanned surface is Sk. 0 <R1 <R2 S1 <0 S2 <(R2 ² −Ymax ² ) ^1/2 −R2 −0.2 ≦ 1−Sk / ft ≦ 0.2 Scanning device. 2. The optical scanning device according to claim 1, wherein said light source means comprises a multi-beam light source having a plurality of light emitting units capable of independently modulating light. 3. The optical scanning device according to claim 1, wherein the shape of the single lens in the main scanning plane is asymmetric with respect to the optical axis of the single lens. 4. The optical scanning device according to claim 1, wherein the axis of symmetry of the single lens in the main scanning direction is tilted and / or shifted with respect to a perpendicular bisector of the surface to be scanned. . 5. The optical scanning device according to claim 1, wherein both lens surfaces of the single lens have their curvatures in a sub-scanning surface continuously changing in a lens effective portion. 6. The horizontal magnification of the single lens in the sub-scanning direction is substantially constant in the lens effective portion.
The optical scanning device according to claim 1. 7. The optical system according to claim 1, wherein the first optical system converts a light beam emitted from the light source means into a substantially parallel light beam, a weakly convergent light beam, or a weakly divergent light beam in the main scanning plane. Optical scanning device. 8. The optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a light beam scanned by the optical scanning device formed on the photosensitive member. A developing device for developing the electrostatic latent image thus formed as a toner image,
An image forming apparatus comprising: a transfer device that transfers a developed toner image to a transfer material; and a fixing device that fixes the transferred toner image to the transfer material.