JP2001033724A - Laser scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-angle laser scanner having excellent image-forming performance. SOLUTION: This scanner is constituted so that a laser beam 2 emitted from a laser beam source 1 is deflected by a polygon mirror 5 so as to scan an image surface 7a of a photoreceptor 7, and it is formed into an image on the image surface 7a by a scanning optical system 6 arranged on an optical path. The optical system 6 is provided with 1st and 2nd scanning lenses 6a and 6b having a surface whose shape in a main scanning direction is asymmetric right and left.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser scanning device applied to a laser printer or the like.

[0002]

2. Description of the Related Art Conventionally, in the field of such a laser scanning apparatus, for example, as described in Japanese Patent Application Laid-Open No. 8-334687, the field curvature of the main scanning is made by using an asymmetric surface in the main scanning direction. And a technique for correcting distortion have been proposed.

[0003]

However, in the configuration described in Japanese Patent Application Laid-Open No. 8-334687, the aberration to be suppressed is asymmetrical despite the two curvatures of field curvature and distortion. Whether the surface is one,
Alternatively, since an asymmetric surface is provided on the front and back of the same lens, the degree of freedom of aberration correction is insufficient, and there is a problem that the correction is limited. The field curvature and the left-right asymmetry of distortion are caused by a polygon mirror that scans an image, and the influence thereof becomes remarkable as the scanning range becomes wider.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a laser scanning device having a wide angle and good imaging performance.

[0005]

In order to achieve the above object, according to the present invention, a laser beam emitted from a light source is deflected by a deflector to scan a surface to be scanned, and is arranged on an optical path. 2. The laser scanning device according to claim 1, wherein said scanning optical system has at least two optical components having surfaces that are asymmetric in the main scanning direction. I do.

[0006] The optical component may be a mirror or a lens.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a schematic configuration of a first embodiment of the laser scanning device of the present invention. As shown in FIG. 1, a laser beam 2 emitted from a laser light source 1 passes through a collimator lens 3 to become parallel light, and then passes through a cylinder lens 4 in the vicinity of a reflection surface 5a of a polygon mirror 5 to perform sub-scanning. Light is collected only in the direction.

Further, the light is deflected by a polygon mirror 5 rotating around a rotation axis 5b as shown by an arrow, and subsequently refracted and reflected by a scanning optical system 6, and condensed on an image surface 7a on a cylindrical photosensitive member 7. To form a latent image. As the polygon mirror 5 rotates, each reflecting surface 5a rotates, and the laser beam 2 scans the rotating image surface 7a on the photosensitive member 7 to draw a latent image. The scanning optical system 6 includes a first scanning lens 6a and a second scanning lens 6 in the order in which the laser beam passes.
b, consisting of a scanning mirror 6c.

FIG. 2 is a diagram showing the shape of the scanning optical system according to the first embodiment of the present invention. FIG. 1A shows a plan view, and FIG. 1B shows a side view. As shown in the figure, the optical axis X (reflected light from the polygon mirror 5 when the deflection angle is 0, the same applies hereinafter) is set on the x axis, the main scanning direction is set on the y axis, and the sub scanning direction is set on the z axis. Here, the arrow A in FIG.
The laser beam 2 is directed from the polygon mirror 5
To the reflection surface 5a.

The point at which the reflection surface 5a and the optical axis X intersect is defined as the origin. In the figure, the scanning mirror 6c is not shown, and the optical path here is drawn as being not bent. Also, in accordance with the surface number of each surface, the reflecting surface 5a of the polygon mirror 5 is denoted by r0, the incident surface of the first scanning lens 6a is denoted by r1, the emitting surface is denoted by r2, and the incident surface of the second scanning lens 6b is denoted by r.
3, the exit surface is r4, and the image surface 7a on the photoconductor 7 is r5.

Table 1 shows the construction data of the scanning optical system. In the table, the reflection surface 5a of the polygon mirror 5, the first scanning lens 6 of the scanning optical system 6,
a, the second scanning lens 6b, and the image surface 7a on the photosensitive member 7 indicate the curvature, the surface interval on the optical axis X, and the refractive index according to the above-described surface numbers. The unit of the numerical value for the length is m
m.

[0012]

[Table 1]

The surface shapes of the second and third surfaces, which are free-form surfaces, are represented by the following equations.

(Equation 1) However, as described above, the coordinate system uses the optical axis as the x-axis, the main scanning direction as the y-axis, and the sub-scanning direction as the z-axis. In the above equation, the term in which z is the 0th order represents the shape of the main scanning. The shape in the sub-scanning section is a parabola, and the term with a quadratic z expresses the curvature near the vertex of the parabola. Also, z
Are all 0, and the vertex of the parabola of the sub-scan section is on the xy plane regardless of the position in the main scanning direction.

In Tables 2 and 3, for the second and third surfaces, respectively, the values of the coefficients a _ij where y is the i-th order and z is the j-th order in the expression of the surface expressed by the above equation (1) are as follows: It is shown by a matrix of i rows and j columns. Here, En (n is an integer) in the table is × 1
Representing a 0 ^n. For example, E-03 becomes × 10 ^-3 .

[0015]

[Table 2]

[0016]

[Table 3]

FIG. 3 is a diagram showing the performance of the scanning optical system in the present embodiment. FIG. 1A shows the field curvature, and FIG. 1B shows the distortion. In (a), the horizontal axis indicates the deflection angle (deg) and the vertical axis indicates the defocus amount (mm), and indicates the field curvature in the sub-scanning direction and the main scanning direction. The curvature of field in the sub-scanning direction is indicated by ◆ and the curve a by a solid line, and the curvature of field in the main scanning direction is ■.
And a curve b by a solid line.

In (b), the horizontal axis represents the deflection angle (de)
g), the distortion (%) is shown on the vertical axis, and the distortion is shown. From the above figures, it can be seen that, in the present embodiment, each of the aberrations is satisfactorily corrected by having two scanning lenses having left-right asymmetric surfaces.

FIG. 4 shows a free-form surface of this embodiment.
This shows only the asymmetric component extracted. FIG. 3A shows the second surface, and FIG. 3B shows the third surface. In each figure, the horizontal axis represents the Y coordinate (mm), and the vertical axis represents the left-right asymmetry (mm).
It can be seen that an asymmetric component as shown in these figures is included in each surface.

FIG. 5 is a diagram showing the superiority of using two left-right asymmetric surfaces. In the same figure, the main scanning of the scanning optical system of the present embodiment is redesigned by changing the way of giving degrees of freedom, and distortion is observed. In order to eliminate the left-right asymmetry, it is preferable to set all the coefficients of the above equation (1) where z is 0th order and y is an odd order. FIG. 11A shows a case where the asymmetry of the second surface is eliminated, and FIG. 10B shows a case where the asymmetry of the third surface is eliminated. From these results, it can be seen that the distortion is greatly increased as compared with FIG. 3B, and that the two surfaces have the left-right asymmetry.

FIG. 6 is a diagram showing the advantage of having two surfaces having left-right asymmetry on different optical components. FIG. 7A shows the field curvature of the main scanning when the third surface is moved in parallel with the main scanning direction by 0.1 mm from the design value and an error is given. The horizontal axis indicates the deflection angle (deg), and the vertical axis indicates the main scanning field curvature (mm). Design values are indicated by ◆ and a curve a by a solid line, and values when an error is given are indicated by ■ and a curve b by a solid line.

On the other hand, FIG. 2B shows a scanning optical system designed to have left-right asymmetry on the second surface and to have left-right asymmetry on the fourth surface in this embodiment in the same manner as described above. , The third surface is moved in parallel to the main scanning direction by 0.1 mm from the design value, and the field curvature of the main scanning when an error is given is observed. Again, the horizontal axis shows the deflection angle (deg) and the vertical axis shows the main scanning field curvature (mm). The design value is indicated by ◆ and the curve a by a solid line, and the value when an error is given is ■. And a curve b by a solid line.

Comparing FIGS. 3A and 3B, when the surface having left-right asymmetry is changed from the second surface to the fourth surface,
In design, the performance of the main scanning field curvature is almost the same as that of this embodiment, but when an error is given, a large difference occurs in the performance. This is the third surface and the fourth surface, that is, the second surface
When the right and left asymmetry is given to the front and back surfaces of the scanning lens 6b, the effect of the front surface and the back surface is similar, so that the effect of two surfaces does not appear unless a large left / right asymmetry is given to each surface.

FIG. 7 is a diagram showing the shape of the scanning optical system in such a comparative example. As described above, the third surface (r3) and the fourth surface (r4), which are the front and back surfaces of the second scanning lens 6b, have left-right asymmetry. However,
Such a shape having a large curvature is not only susceptible to errors, but also causes difficulties in manufacturing, leading to an increase in cost and a decrease in performance.

FIG. 8 is a diagram showing the shape of a scanning optical system according to the second embodiment of the present invention. FIG. 1A shows a plan view, and FIG. 1B shows a side view. As shown in the figure, the optical axis X (reflected light from the polygon mirror 5 when the deflection angle is 0, the same applies hereinafter) is set on the x axis, the main scanning direction is set on the y axis, and the sub scanning direction is set on the z axis. Here, the arrow A in FIG.
The laser beam 2 is directed from the polygon mirror 5
To the reflection surface 5a.

The point at which the reflecting surface 5a and the optical axis X intersect is defined as the origin. In the figure, the scanning mirror 6c is not shown, and the optical path is drawn as being not bent. Further, according to the surface number of each surface, the reflecting surface 5a of the polygon mirror 5 is designated as r0, the incident surface of the first scanning lens 6a is designated as r1, and so on.
The exit surface is r2, the entrance surface of the second scanning lens 6b is r3, the exit surface is r4, and the image surface 7a on the photoconductor 7 is r5.

Table 4 shows the construction data of the scanning optical system. In the table, the reflection surface 5a of the polygon mirror 5, the first scanning lens 6 of the scanning optical system 6,
a, the second scanning lens 6b, and the image surface 7a on the photosensitive member 7 indicate the curvature, the surface interval on the optical axis X, and the refractive index according to the above-described surface numbers. The unit of the numerical value for the length is m
m.

[0028]

[Table 4]

Tables 5 and 6 show that, for the second and fourth surfaces, respectively, the values of the coefficients a _ij where y is the i-th order and z is the j-th order in the expression of the surface expressed by the above equation (1) are as follows: It is shown by a matrix of i rows and j columns. Here, En (n is an integer) in the table is × 1
Representing a 0 ^n. For example, E-03 becomes × 10 ^-3 .

[0030]

[Table 5]

[0031]

[Table 6]

FIG. 9 is a diagram showing the performance of the scanning optical system according to the present embodiment. FIG. 1A shows the field curvature, and FIG. 1B shows the distortion. In (a), the horizontal axis indicates the deflection angle (deg) and the vertical axis indicates the defocus amount (mm), and indicates the field curvature in the sub-scanning direction and the main scanning direction. The curvature of field in the sub-scanning direction is indicated by ◆ and the curve a by a solid line, and the curvature of field in the main scanning direction is ■.
And a curve b by a solid line.

In (b), the horizontal axis represents the deflection angle (de)
g), the distortion (%) is shown on the vertical axis, and the distortion is shown. From the above figures, it can be seen that, in the present embodiment, by having two scanning lenses having left-right asymmetric surfaces, each aberration is substantially well corrected.

FIG. 10 is a view showing the shape of a scanning optical system according to the third embodiment of the present invention. FIG. 1A shows a plan view, and FIG. 1B shows a side view. As shown in the figure, the optical axis X is the x axis, the main scanning direction is the y axis, and the sub scanning direction is the z axis.
Taken on the axis. Here, the laser beam 2 is incident on the reflection surface 5a of the polygon mirror 5 from the direction indicated by the arrow A in FIG. Further, the light is deflected by the polygon mirror 5 rotating around the rotation axis 5b, subsequently reflected by the first mirror 8a and the second mirror 8b of the scanning mirror 8, and condensed on the image surface 7a on the cylindrical photosensitive member 7. To form a latent image.

As the polygon mirror 5 rotates, each reflecting surface 5a rotates, and the laser beam 2 scans the rotating image surface 7a on the photosensitive member 7 to draw a latent image. The point at which the reflection surface 5a and the optical axis X intersect is defined as the origin.
Table 7 shows the surface coordinates of each surface of the scanning optical system. In the table, the positions and orientations of the first mirror 8a, the second mirror 8b, and the image plane 7a (evaluation plane) on the photoconductor 7 are determined by using the origin, x-axis vector, and y-axis vector of the local coordinate system of each plane. Expressed in shape. The unit of the numerical value related to the length is mm.

[0036]

[Table 7]

Tables 8 and 9 show that, for the mirror surfaces of the first mirror 8a and the second mirror 8b, respectively, the coefficient a of the i-th order and z of the j-th order in the expression of the surface shown in the above equation (1). _ij
Are indicated by a matrix of i rows and j columns. Here, En (n is an integer) in the table represents × 10 ⁿ . For example, E-
04 becomes × 10 ^-4 .

[0038]

[Table 8]

[0039]

[Table 9]

FIG. 11 is a diagram showing the performance of the scanning optical system in this embodiment. FIG. 1A shows the field curvature, and FIG. 1B shows the distortion. In (a), the horizontal axis indicates the deflection angle (deg) and the vertical axis indicates the defocus amount (mm), and indicates the field curvature in the sub-scanning direction and the main scanning direction. The curvature of field in the sub-scanning direction is indicated by ◆ and the curve a by a solid line, and the curvature of field in the main scanning direction is ■.
And a curve b by a solid line.

In (b), the horizontal axis represents the deflection angle (de)
g), the distortion (%) is shown on the vertical axis, and the distortion is shown. From the above figures, it can be seen that, in the present embodiment, by having two scanning mirrors having left-right asymmetric surfaces, each aberration is substantially well corrected.

FIGS. 12 to 16 are perspective views schematically showing the mirror surface or lens surface shape of the scanning optical system. In each figure, the mirror surface or lens surface S of the surface shape represented by the above equation 1 is shown in a lattice shape. First,
FIG. 12 shows a zero-order surface shape in which z is a zero-order plane. A cross section parallel to the xz plane is a straight line along the z-axis, and the straight line moves in the x-axis direction as it moves in the y-axis direction. It is of such a shape.

Next, FIG. 13 shows a primary surface shape in which z is linear. The cross section parallel to the xz plane is a straight line, and the straight line rotates as it moves in the y-axis direction, and has a twist. It is of such a shape. Further, FIG. 14 shows a quadratic surface shape in which z is a quadratic surface, and a cross section parallel to the xz plane is a quadratic curve, and the shape of the quadratic curve changes as it moves in the y-axis direction. is there.

FIG. 15 shows a cubic surface shape in which z is tertiary. A cross section parallel to the xz plane is a cubic curve, and y is
The shape of the cubic curve changes as it moves in the axial direction. Finally, FIG. 16 is a view obtained by synthesizing the surface shapes in which the above-mentioned z is 0th to 3rd order. In this manner, various surface shapes represented by a polynomial expression of y having various degrees of z are selected and synthesized, and the surface shape of the mirror surface or the lens surface is determined.

The light source referred to in the claims corresponds to the laser light source in the embodiment. Hereinafter, the deflector will be a polygon mirror, the surface to be scanned will be on the image surface of the photoreceptor, and the optical component will be a scanning lens. Alternatively, each corresponds to a scanning mirror.

[0046]

As described above, according to the present invention,
By having two optical components with asymmetrical surfaces,
It is possible to provide a laser scanning device having a wide angle and good imaging performance.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a shape of a scanning optical system according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the performance of the scanning optical system according to the first embodiment of the present invention.

FIG. 4 shows a free-form surface according to the first embodiment of the present invention.
The figure which extracts and shows only an asymmetric component.

FIG. 5 is a diagram showing the superiority of using two left-right asymmetric surfaces.

FIG. 6 is a view showing an advantage that two surfaces having left-right asymmetry are on different optical components.

FIG. 7 is a diagram showing a shape of a scanning optical system in a comparative example.

FIG. 8 is a diagram illustrating a shape of a scanning optical system according to a second embodiment of the present invention.

FIG. 9 is a diagram illustrating the performance of a scanning optical system according to a second embodiment of the present invention.

FIG. 10 is a diagram illustrating a shape of a scanning optical system according to a third embodiment of the present invention.

FIG. 11 is a diagram showing the performance of a scanning optical system according to a third embodiment of the present invention.

FIG. 12 is a perspective view schematically showing a mirror surface or a lens surface shape of a scanning optical system (z is the 0th order).

FIG. 13 is a perspective view schematically showing a mirror surface or a lens surface shape of the scanning optical system (z is primary).

FIG. 14 is a perspective view schematically showing a mirror surface or a lens surface shape of a scanning optical system (z is secondary).

FIG. 15 is a perspective view schematically showing a mirror surface or a lens surface shape of a scanning optical system (z is tertiary).

FIG. 16 is a perspective view (synthesis) schematically showing a mirror surface or a lens surface shape of the scanning optical system.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 laser beam 3 collimator lens 4 cylinder lens 5 polygon mirror 6 scanning optical system 7 photoconductor 8 scanning mirror

Claims (2)

[Claims] 1. A laser scanning system in which a laser beam emitted from a light source is deflected by a deflector to scan on a surface to be scanned, and an image is formed on the surface to be scanned by a scanning optical system arranged on an optical path. In the apparatus, the scanning optical system has at least two optical components having surfaces that are asymmetric in the main scanning direction. 2. The laser scanning device according to claim 1, wherein the optical component is a mirror or a lens.